Mechanism and Farmers' Perception of Mixed Variety Planting

MECHANISM AND FARMERS’ PERCEPTION OF MIXED
VARIETY PLANTING FOR THE MANAGEMENT
OF RICE TUNGRO DISEASE
YUJI SHIBATA
SUBMITTED TO THE FACULTY OF THE GRADUATE SCHOOL
UNIVERSITY OF THE PHILIPPINES LOS BAÑOS
IN PARTIAL FULFILLMENT OF THE
REQUIREMENTS FOR THE
DEGREE OF
MASTER OF SCIENCE
(Plant Pathology)
JULY 2006

The thesis attached hereto, entitled “MECHANISM AND FARMERS’
PERCEPTION OF MIXED VARIETY PLANTING FOR THE MANAGEMENT
OF RICE TUNGRO DISEASE” prepared and submitted by YUJI SHIBATA in partial
fulfillment of the requirements for the degree of MASTER OF SCIENCE (PLANT
PATHOLOGY) is hereby accepted.
MARIO V. PERILLA IL-RYONG CHOI
Member, Guidance Committee Co-Chair, Guidance Committee
________________________ ________________________
Date signed Date signed
EDNA Y. ARDALES
Chair, Guidance Committee
______________________
Date signed
Accepted as partial fulfillment of the requirements for the degree of MASTER OF
SCIENCE (PLANT PATHOLOGY).
VIRGINIA R. OCAMPO
Director, Crop Protection Cluster
_____________________________
Date signed
ERNESTO V. CARPIO
Dean, Graduate School
University of the Philippines Los Baños
______________________________
Date signed
ii

BIOGRAPHICAL SKETCH
The author was born on August 26, 1976 as the third of child of Kouichi Shibata
and Fumie Shibata in Showa, Saitama, Japan. He received his elementary education from
Houshubana elementary school and his secondary education from Edogawa junior high
school in Showa and Kasukabe high school in Kasukabe and graduated in 1994.
In 1997, he enrolled at the Tokyo University of Agriculture (TUA) taking up
Bachelor of Science in Agriculture major in International Development of Agriculture
where he graduated in 2001. He developed an interest in plant viruses and tropical
agriculture in Southeast Asia since he joined the Laboratory of Tropical Crop Protection
during his junior and senior years at TUA.
After college, he decided to pursue his MSc degree in Plant Pathology at the
University of the Philippines Los Baños (UPLB) in 2001. In July, 2004 he was granted a
MS-Thesis Research Scholarship and worked at the Entomology and Plant Pathology
Division (EPPD) as a MS-Research Scholar at International Rice Research Institute
(IRRI).
He is a member of the Philippines Phytopathological Society (PPS)
iii
YUJI SHIBATA

ACKNOWLEDEMENT
For their invaluable support and contributions in the completion of this MSc.
Thesis, the author would like to express his sincerest gratitude and appreciation to the
following individuals and organizations.
Dr Edna Y, Ardales, Chairman of the Guidance Committee, Crop Protection
Cluster, UPLB, for her kind encouragement, and meaningful suggestions in improving
the manuscript.
Dr Il-Ryong Choi, Co-Chair of the Guidance Committee, for the direction and
guidance in the conduct of the experiment, his constructive comments, suggestions, and
deep insight in the preparation of the outline and manuscript.
Dr Mario V. Perilla, member of the Guidance Committee, for his suggestions and
criticism in the improvement of the manuscript.
Mr. Rogelio C. Cabunagan, in-house adviser at IRRI, for his unselfish and
continuous support during the conduct of the experiment and the improvement of the
manuscript.
Mr. Mario Izon, Panfilio Domingo, Esquirion Baguioso, for their expertise and
unlimited support during the conduct of the experiment.
Mrs. Violeta Bartolome and Adoracion Resurreccion for their expertise and kind
assistance in the statistical data analysis and the improvement of the manuscript.
All the research scholars in the department especially Mr. Neggussie Shoatatek
Zenna for the valuable discussions, his brilliant brotherhood and his moral support.
Drs. Nobuya Kobyashi, Kumi Yasunobu, Yoshinobu Nitta, Yolanda F. Chen,
Yuichiro Furukawa, and Yuka Sasaki, and Yasukazu Hosen for their warm
encouragement and meaningful suggestions in the preparation of the survey and for
improving the manuscript.
All his friends not only in the Philippines but also in the world, for their
continuous friendship despite of the distance.
Dr. Luis Rey I. Velasco, Chancellor of UPLB, for his respectful support and
sponsorship during the graduate study at UPLB.
To my parent for their understanding of his study and inspirational and moral
support through out the study.
iv

TABLE OF CONTENTS
TITLE PAGE i
APPROVAL PAGE ii
PAGE
BIOGRAPHICAL SKETCH iii
ACKNOWLEDGEMENT iv
TABLE OF CONTENTS v
LIST OF TABLES ix
LIST OF FIGURES xi
LIST OF APPENDIX TABLES xiii
ABSTRACT xiv
INTRODUCTION 1
REVIEW OF LITERATURE 8
Rice Tungro Disease 8
Economic Importance 8
The Rice Tungro Viruses 9
Symptom 10
Transmission 11
Disease Development in the Field 12
Disease Management 14
Resistance to Rice Tungro Disease 17
Varietal Mixtures as RTD Management Option 18
Importance of Farmers’ Perception Survey 23
v

PAGE
Farmers’ Preference for Grain Quality 25
MATERIALS AND METHODS 26
Plant Materials 26
Insect Vector 26
Viruses 27
Assay Procedure for RTBV and RTSV infection. 27
Biological Characterization of Matatag 9 Resistance to Rice Tungro Disease 28
Forced Test Tube Inoculation 28
Relative Quantification of RTBV and RTSV in Matatag 9 and IR64 29
Preparation of samples 29
Optimum assay condition 29
Characterization of virus replication 30
Biological Characterization of Matatag 9 Resistance to Green Leafhopper 30
GLH Preference and Tungro Viruses Transmission 30
Adult Insect longevity 32
Nymphal Mortality 32
Growth and Development of Nymph 33
Performance Evaluation of Varietal Mixture components 35
Comparative Morphological and Yield Characteristics of Matatag 9 and IR64 35
Effect of mixed planting of resistant and susceptible varieties on the incidence
of rice tungro disease
Tray Inoculation and Experimental Design 36
Mixed seed planting layout 37
Interplanting (row mixture) layout 39
vi
36

PAGE
Serial Inoculation in Resistant and Susceptible Varieties 42
Farmers’ Perception Survey on the Use of Mixed Seed Planting 43
Description of Survey Site 43
Survey Procedure 43
Grain Quality Evaluation of Mixed Seed Planting 45
Rice Grains Used 45
Milling Quality 45
Grain Size, Shape and Appearance 46
Amylose Content 47
Gelatinization Temperature 47
Gel Consistency 47
RESULTS AND DISCUSSION 49
Biological Characterization of Matatag 9 Resistance to Rice Tungro Disease 49
Rates of Infection with RTSV and RTBV under Different Inoculum
Levels
Temporal Change in Apparent Rates of Infection with RTSV and
RTBV
Temporal Change in The Accumulation of Tungro Viruses 51
Biological Characterization of Matatag 9 Resistance to Green Leafhopper 57
Settling preference 57
Adult Insect longevity 59
Nymphal Mortality 59
Growth and Development of GLH Nymph 61
Performance Evaluation of Varietal Mixture Components 65
Comparative Morphological and Yield Characteristics of Matatag 9 and IR64 65
vii
49
49

Effect of mixed planting of resistant and susceptible varieties on the incidence
of rice tungro disease
PAGE
Serial-Inoculation in Resistant and Susceptible varieties 70
Farmers’ Perception Survey on the Use of Mixed Seed Planting 75
Respondents’ profile. 75
Farm profile 75
Farmers’ awareness and knowledge of rice tungro disease 80
Farmers’ awareness of rice tungro disease control 81
Awareness of mixed seeds planting 83
Grain Quality Evaluation of Mixed Seed Planting 91
Milling Quality 91
Grain Size, Shape and Appearance 92
Amylose Content and Gelatinization Temperature 95
Gel Consistency 96
Sensory evaluation of cooked rice 96
SUMMARY AND CONCLUSIONS 100
RECOMMENDATIONS 105
LITERATURE CITED 106
APPENDIX 124
viii
68

LIST OF TABLES
TABLE PAGE
1 Ratios of seed mixtures used for mixed variety planting 36
2 Combination of Matatag 9 and IR 64 for serial transmission 42
3 Classification for grain size (a) and shape (b) 46
4 Numerical scale for scoring gelatinization temperature (GT) 47
5 Infection rate (%) of RTBV and RTSV at time of initial sampling
and 60 DAI: 6-day-old seedling
6 Infection rate (%) of RTBV and RTSV at time of initial sampling
and 60 DAI: 21-day-old seedling
7
Average seedling infection (%) and average number of alighted
insect per 5 seedlings of IR64 and Matatag 9 at different
observation times from the GLH preference test.
8 Effect of antibiosis factor on GLH behavior and other life history
traits
9 Comparison of tiller number during vegetative stage 67
10 Comparison of agronomic traits of mixture components at harvest 67
11 Comparison of physical characteristics of grain 67
12 Profile of farmer respondents of the survey in Ajuy, Iloilo,
Philippines
13 Varieties planted for the past 4 seasons among 52 respondents in
Ajuy, Iloilo, Philippines
14 Percentage of farmers reporting major pests and diseases on rice
farming in Ajuy, Iloilo, Philippines
15 Farmers’ experience of RTD incidence in their farm and its damage
seriousness ranked by farmers
16 Farmers’ perceptions of causes and spread of RTD 81
ix
52
53
58
60
76
77
79
80

TABLE PAGE
17 Farmers’ control measures for rice tungro disease and perception of
insecticide effectiveness
18 Farmers’ awareness of the availability of tungro resistant variety
and experience of resistant breakdown
19 Major reasons to the termination of the mixed seed planting and its
adaptation constraints in farmers’ field in Ajuy
20 Grain length and width of milled rice harvested from plots planted
to different seed mixture ratio of R (resistant Matatag 9) and S
(susceptible IR64) analyzed by Cervitec 1625 Grain Inspector
21 Degree of chalkiness of milled rice harvested from plots planted to
different seed mixture ratio of R (resistant Matatag 9) and S
(susceptible IR64) analyzed by Cervitec 1625 Grain Inspector
22 Amylose content and gelatinization temperature of milled rice
harvested from plots planted to different mixture ratio of R
(resistant Matatag 9) and S (susceptible IR64)
23 Viscosity analysis of cooked milled rice harvested from plots
planted to different mixture ratio of R (resistant Matatag 9) and S
(susceptible IR64) by the Rapid Visco Analyzer.
x
82
83
85
93
93
95
96

LIST OF FIGURES
FIGURE PAGE
1 Experimental set-up for settling preference experiment. Five 10day-old
seedlings each of test variety planted in a pot were
randomly placed inside a plastic cage.
2 Experimental set-up for growth and development of GLH nymph
test among four test varieties.
3 Example of seed layout of T2 (75:25 for Matatag 9 and IR64) seed
mixtures for tray inoculation: R indicates position of resistant
variety, Matatag 9 and S indicates position of susceptible variety,
IR64.
4 Seed layout of T2. R indicates position of resistant variety, Matatag
9 and S indicates position of susceptible variety, IR64.
5 Seed layout of T3. R indicates position of resistant variety, Matatag
9 and S indicates position of susceptible variety, IR64.
6 Seed layout of T4. R indicates position of resistant variety, Matatag
9 and S indicates position of susceptible variety, IR64.
7 The site (shaded red) of the survey in the municipality of Ajuy,
Iloilo Province, Philippines
8 Infection rate of RTBV and RTSV in three varieties with 1, 3, and
5 viruliferous GLH by the forced test tube inoculation.
9 Temporal pattern of RTBV and RTSV accumulation in Matatag 9
and IR64. Both 6-day-old and 21-day-old seedlings were used at
inoculation.
10 Symptom caused by RTD on Matatag 9 (left) and IR64 (Right).
Matatag 9 did not show typical RTD symptom as compared with
IR64 which showed yellowing and stunting symptom.
11 Temporal changes in the number of viruliferous GLH on the
seedlings of IR64 and Matatag 9.
12 Morphological appearance of Matatag 9 (left) and IR64 (right) at
the 107 DAT in the screenhouse.
xi
31
34
38
39
40
41
44
50
55
56
58
66

FIGURE PAGE
13 Growth comparison between Matatag 9 and IR64 at 15 days
interval after transplanting.
14 Relative rates of infection with RTBV+RTSV (RBS), total RTBV
(RTB), and total RTSV (RTS) observed in mixed seed plantings
and interplantings. The relative rates were computed based on
those observed in the pure stand of IR64 (100% S).
15 Duration of virus retention ability through 5 days serial-inoculation
with different combinations of resistant and susceptible varieties.
16 Farmers’ awareness of the mixed seed planting for rice tungro
disease control (A), their belief of control effectiveness (B), and
experience of the mixed seeds planting in their field (C).
17 Milling yield of the rough rice harvested from plots planted to
different seed mixture ratio of R (resistant Matatag 9) and S
(susceptible IR64).
18 Percentage of whole grain and broken rice from rough rice
harvested from plots planted to different seed mixture ratio of R
(resistant Matatag 9) and S (susceptible IR64) analyzed by Cervitec
1625 Grain Inspector
19 Grain appearance of rough rice (paddy) and milled rice from each
treatment.
20 Viscosity curves of cooked milled rice harvested from plots
planted to different mixture ratio of R (resistant Matatag 9) and S
(susceptible IR64) by the Rapid Visco Analyzer
xii
66
69
71
84
91
92
93
97

LIST OF APPENDICES
Appendix PAGE
1 Questions for socioeconomic survey in Ilo-ilo. 124
xiii

ABSTRACT
YUJI SHIBATA, University of the Philippines Los Baños, July 2006.
Mechanism and Farmers’ Perception of Mixed Variety Planting for the
Management of Rice Tungro Disease.
Major Professors: Dr. Edna Y. Ardales and Dr. Il-Ryong Choi
To characterize the resistance of Matatag 9 against rice tungro disease (RTD),
Matatag 9 and an RTD-susceptible variety IR64 were evaluated for their reactions to
tungro viruses and the insect vector (green leafhopper, GLH). The results indicated that
low RTD incidence in Matatag 9 was mainly due to the resistance against GLH, although
the contribution of moderate resistance against tungro viruses may not be excluded. The
agronomical characteristics of Matatag 9 were found to be similar to those of IR64,
therefore, it is suitable for mixed planting. Mixed seed planting was more effective in
reducing RTD incidence than interplanting, suggesting that the random spatial
distribution of resistant plants is critical for the reduction of RTD in fields. Survey
conducted among the farmers in an RTD endemic area indicated that besides the impact
on disease reduction, the grain quality is an important criterion for them to adopt the
mixed seed planting. The quality of grains produced through mixed seeds planting of
Matatag 9 and IR64 appeared to be comparable to that of IR64. Collectively, these
suggest that the mixed seed planting between Matatag 9 and IR64 may be able to offer
both yield stability and high grain quality in RTD-endemic areas.
xiv

INTRODUCTION
Rice plants are farmed mainly for the grain used for human consumption in over
one hundred countries around the world (Maclean et al. 2002). The farmers of Asia till 90
percent of the total world’s rice fields and this accounts for 92 percent of the global rice
production. Moreover, Asia is home to 59 percent of the world’s population and the rice
consuming population is growing at 2 percent a year. In humid and sub-humid Asia, rice
is the primary staple food (Khush, 1997), and directly supplies approximately 21 percent
of human per capita energy and 15 percent per capita protein each year. Together with
wheat and maize, rice provides over 50 percent of all of the calories that are annually
consumed by the entire human population (Maclean et al. 2002). The population is
expected to increase by 58 percent over the next 35 years. Recent projections indicate
that the demand for rice production in 2025 is expected to be 765 million that is 70
percent more rice than is produced today (Maclean et al. 2002). Consequently the annual
output must increase by over 5 million tones a year just to keep pace with population
growth (Maclean et al. 2002).
Cultivation of modern varieties of rice was widely accepted by farmers in Asia to
earn more income. This replaced the local varieties, eventually resulting in low diversity
of cultivated ones and made the modern varieties more vulnerable to pests and diseases.
Narrow spacing in planting rice also resulted in high density crops and in turn altered the
microclimate under the short canopy of rice stands making it more favorable for the

development of not only the beneficial, but also harmful flora and fauna in the rice
ecosystem (Azzam and Chancellor, 2002; Sogawa, 1976; Thresh, 1982).
Tungro identified as a leafhopper-borne disease was first observed in the
Philippines at the experimental farm of the International Rice Research Institute (IRRI) in
1963 (Rivera and Ou, 1965). Rice tungro disease (RTD) is a destructive rice disease
widely distributed in almost all South and South-east Asia and some parts of East Asia
countries like Japan, China, Thailand, Philippines, India and Indonesia.
Substantial yield losses have been reported when the RTD outbreak occurred. For
example, in 1971 the estimated yield loss due to RTD was 456,000 tons of rough rice in
Central Luzon and Cotabato where IR5, IR8, IR22 and IR24 were widely cultivated. In
1993 in Davao del Norte, a total of 2265 tons amounting to about US$ 40,000 were lost
due to the RTD (Baria, 1993). Shinkai (1977) reported that a total yield loss due to rice
waika virus, which is phylogenetically similar to rice tungro spherical virus (RTSV), was
approximately 10,000 tons in 1973 in Kyushu, Japan.
RTD epidemic is unpredictable and once it occurs no control measures can be
applied. In the late 1960’s and early 1970’s, severe epidemics caused by RTD resulted in
major production losses in Bangladesh, India, Indonesia, Malaysia, Philippines and
Thailand. In the Philippines specifically, major epidemics occurred in 1957, 1962, 1969-
71, 1983-1984, and 1987 (Koganezawa, 1998). Although several control methods against
RTD were proposed and applied, epidemics reoccur periodically. Extensive cultivation of
susceptible varieties was identified as one of the potential factors influencing the disease
epidemics (Holt et al. 1996; Cabunagan et al. 2001). Thus, in the above countries,
2

varietal resistance to RTD is an important breeding objective for rice improvement
(Khush and Virmani, 1985). The use of resistant varieties is considered as the most
economical and environmentally sound strategy for management of RTD. Also, the use
of resistant varieties has been very effective for incidence of RTD could be drastically
reduced the following year after its introduction (Sogawa, 1976).
Screening rice germplasm for RTD resistance started as early as 1963 at IRRI and
breeding program was started in 1966-1967 (Khush, 1977). Several resistant varieties,
Peta, Intan, Sigadis, TKM6, HR21, Malagkit Sungsong, Gam Pai30-12-15, Ptb18,
Pankhari203 and BJ1 were identified and used as donor parents. In the initial stage,
selected resistant varieties had only vector resistance because of the screening methods
adapted in the breeding programs. The screening of breeding materials has been done
generally in the field where tungro incidence is low and vector resistant varieties are
always selected (Hibino et al. 1987). Lack of appropriate diagnostic techniques made the
analysis of resistance to tungro viruses difficult. Vector resistant varieties escape RTD
infection under light to moderate vector pressure but succumb to infection under high
vector pressure (Cabunagan et al. 1987). Reaction also changes with change in virulence
of GLH vector in the field (Dahal et al. 1990). The differentiation between resistance to
the tungro viruses and resistance to the GLH vector is important in the development of
varieties with durable resistance. In fact, resistance to the tungro viruses is nowadays
regarded as crucial to any long-term management of the RTD problem in South and
Southeast Asia.
3

With the new understanding of the tungro viruses and the availability of
serological techniques such as enzyme linked immunosorbent assay (ELISA) in the early
1980’s, research on RTD resistance has shifted to virus resistance, which may be more
effective and durable (Khush et al. 2004). Since the start of the mass screening for RTD
resistance at IRRI in 1963 about 30% of the total IRRI Rice Germplasm Center
Accession (IRGC Acc) so far has been screened for RTD resistance. The results revealed
that most of the resistant accessions originated from Bangladesh, India, Pakistan, and
Indonesia (Cabunagan and Koganezawa, 1993). Many IRGC accessions have been
reported as resistant to RTSV infection (Hibino et al. 1990; Koganezawa and Cabunagan,
1997). Although sources for resistance to rice tungro bacilliform virus (RTBV) infection
have yet to be found in rice germplasm at IRRI, several varieties show symptomatic
resistance or tolerance (Hibino et al. 1990; Koganezawa and Cabunagan, 1997). The term
“tolerance” refers to varieties that show no or mild symptom and no marked yield loss
when infected, regardless of virus concentration. Multiplication of RTBV is suppressed
in some tolerant varieties such as Utri Merah, Balimau Putih and Utri Rajapan, and
sometimes virus concentration is too low to be detected by ELISA (Takahashi et al.
1993; Cabunagan et al. 1993).
Recently, varieties resistant to tungro viruses (e.g., the Matatag lines) have been
developed (Angeles et al. 1998; Cabunagan et al. 1999) and deployed in selected areas
where rice tungro was endemic, in the Philippines. As there are only limited resistance
sources against the tungro viruses, it is important to develop a deployment strategy that
would exert minimal selection pressure on the viruses so as to minimize the occurrence of
4

esistance-breaking strains due to monoculture, thus prolong the lifespan of these
resistant varieties.
In the history of rice production, wide adoption of modern varieties with
resistance to specific pathogens in a large area often results in genetic uniformity which
predisposes the crop system to disease epidemics. In order to avoid stepping in such
pathway of rice cultivation with the tungro virus resistant varieties, it is critical to deploy
resistant varieties based on understanding of the pathogen population structure as well as
to maintain genetic diversity in the fields. It was suggested that genetic diversity in
agricultural settings reduces selection pressure against pathogens to slow down pathogen
evolution and provides greater disease suppression when used over large areas (Leung et
al. 2003). Although there have been a number of reports on the application of variety
mixtures to suppress the disease of small grain crops caused by fungal pathogens (Finckh
et al. 2000; Mundt, 2002 and references therein), only few attempts were made to
examine the effects of variety mixture on the incidence of viral disease (Hariri et al.
2001; Pedroso, 2001; Power, 1991).
Experiments were conducted in Iloilo, Philippines to assess the effects of variety
mixed planting of resistant (Matatag 9) and susceptible (IR64) varieties on the occurrence
of RTD and the frequency of RTD components in this endemic area. The advantages of
the seed mixtures in RTD suppression and yield stability in the tungro endemic area of
Iloilo were observed in the study (Cabunagan et al. 2004, Cabunagan and Choi, 2005).
However, more performance data on the seed mixtures under high disease pressure are
needed to evaluate if this control measure is still effective and can provide stable yield.
5

There is no clear explanation of RTD reduction in the previous study, therefore, it
is necessary to determine the mechanism for the reduction of RTD in mixed planting of
resistant and susceptible varieties. There are two types of resistance to rice tungro
disease: (1) resistance to the vector- the leafhopper cannot feed and reproduce effectively
on resistant plant and thus cannot transmit tungro viruses, (2) resistance to the virus- the
virus cannot survive and multiply inside the plant. Thus, it is important to biologically
characterize the mechanism of resistance of the resistant component Matatag 9 and how
this relates to tungro viruses transmission.
In addition, in order to transfer successfully the new tungro disease management
scheme to the farmers, it is important to evaluate farmers’ perception on the use of mixed
seeds planting of resistant and susceptible varieties for the management of rice tungro
disease because the first step to improve rice farmers’ RTD management capabilities is to
gain their acceptance of the new management scheme. Surveys provide a useful way to
canvas the ideas and opinions of farmers about pest and disease management while at the
same time documenting their current practices.
As a component of the mixed seed planting, resistant variety Matatag 9 was
chosen because it has more or less similar plant type, eating quality and maturity date to
the susceptible IR64 so that farmers could still cultivate IR64 even in RTD endemic areas.
To answer the question "is the grain quality of the mixed seeds comparable to the pure
IR64 which is preferred by the farmers and millers" grain quality characteristics of the
mixtures with the pure Matatag 9 or pure IR64 were compared in this study. Specifically,
6

data on milling potentials, physical attributes and physicochemical characteristics were
examined.
Understanding the mechanism of resistance of Matatag 9, specifically how mixed
seed planting of resistant Matatag 9 and susceptible IR64 reduces RTD incidence,
farmers’ perception of the technology and the grain quality of the mixture compared with
pure IR64 would enable us to predict the sustainability and farmers adaptation of the
variety mixture system for their management of RTD.
The objectives of the study are:
1. To determine how mixed planting of resistant and susceptible varieties influence
the incidence of RTD
2. To determine how planting types and disease pressure affect RTD incidence in
mixed planting of resistant and susceptible varieties.
3. To evaluate farmers’ perception on the use of mixed planting of resistant and
susceptible varieties for RTD management
7

REVIEW OF LITERATURE
Rice Tungro Disease
RTD is one of the most destructive diseases of rice in South and Southeast Asia,
where epidemics of the disease have occurred since the mid-1960s (Azzam and
Chancellor, 2001). In the Philippine dialect Ilocano tungro means degenerated growth.
RTD is also known by various names in different countries; mentek or penyakit habang
in Indonesia, penyakit merah in Malaysia, yellow-orange leaf in Thailand and leaf
yellowing in India. Waika caused by a virus closely related to RTSV one of the viruses
causing RTD was observed in southern Japan. RTD is also reported in Bangladesh, Sri
Lanka, Nepal, southern China and Vietnam (Azzam and Chancellor, 2001).
Economic Importance
RTD is a serious virus disease of rice in South and Southeast Asia since 1960 (Ling
and Tiongco, 1979). It has caused considerable losses in rice production in many
countries in Asia. When the disease occurs in epidemic proportion, it can cause severe
crop damage and reduce yield greater than 85% if cultivars grown are susceptible, and
infected at an early growth stages.
It has been reported that in 1993 alone, the disease has devastated 80,000 hectares
in India (Chowdhury, 1997), about 199,000 hectares in Indonesia (Hasanuddin et al.

1997) and 18,655 hectares in Malaysia, and the total damage was estimated to be nearly
US$10 million (Chen and Jalil, 1997).
In the Philippines, RTD is a continuing problem in Central Luzon, Bicol and
Mindanao, particulary in Cotabato and Davao (Baria, 1993). Serrano (1957) reported that
the stunt disease, which is now considered as RTD, was extremely destructive in the
1940’s throughout the major rice-growing regions of the Philippines and caused a yield
reduction of 1.4 million tons equivalent to 30% overall loss annually. RTD epidemics
were occasionally reported in 1960’s to 1989 by the Municipal Agricultural Offices
throughout the country. Outbreak also occurred in Mindanao in 1993 to 1998 and in
Negros Occidental in 1998, affecting 900 to 2,700 hectares and 700 hectares of rice fields,
respectively.
The Rice Tungro Viruses
RTD is a composite disease caused by rice tungro bacilliform virus (RTBV) and
rice tungro spherical waikavirus (RTSV). RTBV belongs to the genus Badnavirus of the
family Caulimoviridae and RTSV belongs to the genus Waikavirus of the family
Sequiviridae (Mayo and Pringle, 1997). Virus particles of RTBV are bacilliform, 100-300
nm in length and 30-35 nm in width. RTBV has a circular 8-kbp double stranded DNA
genome and a single capsid protein (Hull, 1996). Virus particles of RTSV are polyhedral,
about 30 nm in diameter. RTSV has 12kb single stranded RNA genome and three capsid
proteins (Shen et al. 1993). It appears that RTBV depends on the helper components
9

produced by RTSV for its own transmission and is mainly responsible for the severe
RTD symptoms.
Symptoms
RTD symptoms are often confused with insect infestation and nutritional disorders
such as nitrogen and iron deficiency (Satapathy et al. 2001). Rice plants infected with
RTBV and RTSV show symptoms such as stunting, yellow or yellow-orange
discoloration of the leaves, and reduced tillering (Hibino et al. 1978). Discolored leaves
may show irregularly shaped dark-brown blotches. The leaves, especially the younger
ones, may show striping or mottling and interveinal chlorosis. The first symptom on
young seedlings at one week after inoculation is incomplete emergence of the youngest
leaf and interveinal chlorosis (Sogawa, 1976). The plant gradually displays more
prominent red discoloration, which usually develops from tip to the base of the leaves,
interveinal stripes, and small brown irregular rusty spots (Hasanuddin and Hibino, 1989).
Symptoms of interveinal and systemic necrosis usually appear in Oryza glaberrima and
O. barthii when they are infected with tungro viruses (Rao et al. 1978; Kobayashi et al.
1992). Plants infected with RTBV alone show similar but milder symptoms than that
caused by double infection. Plants infected with RTSV alone show no obvious symptoms
except very mild stunting. In infected plants, RTBV is localized in the vascular bundles
and RTSV in the phloem tissues (Sta Cruz et al. 1993).
10

Transmission
The rice tungro viruses; RTBV and RTSV are transmitted in a non-circulative,
semi-persistent manner by Nephotettix virescens, N. nigropicutus, N. cincticeps, Recilia
dorsalis, and some other Nephotettix spp. N. virescens is the most efficient vector of RTD.
The other species are considered as minor vectors (Hibino, 1996). It is generally known
that tungro viruses are not transmitted through any other routes such as pollen, seeds, soil
and plant sap (Nish et al. 1975). Females of N. virescens transmit RTD more efficiently
than males (Lamey et al. 1967; John, 1968). It is reported that the minimum acquisition
and inoculation feeding periods for N. virescens are 5 min and 7 min, respectively (Ling,
1972). N. virescens retains RTD infectivity for 2 to 6 days but loses infectivity after
molting (Ling, 1972). Hibino et al. (1978) reported that green leafhopper (GLH) can
retain RTBV for 4-5days and RTSV for 2-4days. They readily acquire RTSV from plants
infected with RTSV alone, but do not acquire RTBV from plants infected with RTBV
alone. GLH can acquire RTBV only when exposed to RTSV-infected plants before
feeding on RTBV-infected plants (Hibino, 1983; Hibino et al. 1979). It is speculated that
through feeding on plants infected with RTSV, GLH gain a helper component and thus
the ability to acquire RTBV, and may retain the helper activity for the acquisition of
RTBV for seven days (Hibino et al. 1987). RTSV-infected plants may serve as the source
of helper factor for transmission as early as 36 hr after inoculation and as the virus source
72 hr after inoculation (Chowdhury et al. 1990). Dahal et al. (1990b) reported that
viruliferous GLH usually feed from the xylem on leafhopper-resistant cultivars, and
11

transmit predominantly RTBV alone, whereas GLH feed mainly from the phloem on
susceptible cultivars and can transmit both RTBV and RTSV efficiently.
Disease Development in the Rice Field
Several factors such as plant age, cultivars, abundance of initial virus inoculum,
population of vector, cultural practices, and environmental factors may affect the
development of RTD in the field (Shukla and Anjaneyulu, 1981b and 1981c; Anjaneyulu,
1986; Cabunagan et al. 2001).
Ling and Palomar (1966) reported a reduction in the percentage of rice plants
showing symptoms with increasing plant age at the time of inoculation. Gibbs and
Harrison (1976) also reported plants are most susceptible to infection when young and
often most suitable as host for vectors, whereas plants tend to be more resistant to
infection as they grow, thus, making multiplication of viruses and spread of disease
slower during this stage.
Extensive cultivation of susceptible varieties is considered as the main factor
favoring the disease epidemics (Loevinsohn, 1984; Holt et al. 1996). Hibino (1996)
pointed out that the continuous use of cultivars of the same genetic background in wider
scale farming often led to RTD epidemic because of the establishment of favorable
condition for the development of viruses and the survival of insect vectors.
Lapis (1991) reported the variability of inoculum is one of the factors making
RTD occurrence unpredictable. When the outside source of inoculum is higher
12

particularly during the wet season, the effect of introduced sources of inoculum was more
difficult to detect (Thresh, 1976). Moreover, virus transmission increased as the number
of source plants increased (Chowdhury et al. 1994).
The dispersal of the RTD by the vector seems to be also affected by the levels of
humidity (Kondaiah et al., 1976). RTD incidence is generally higher during the wet than
during dry season, although it is unclear if this is due to a higher number of GLH
(Tiongco et al. 1993).
The levels of vector population may correlate with those of RTD incidence. It was
reported that the chance for RTD to spread in the field was on average highest at 6 weeks
after transplanting when the first generation large nymphs of N. virescens were most
abundant (Suzuki et al. 1992). In another study conducted by Savory et al. (1993) showed
that in RTD-endemic area, the higher RTD incidence was associated with increasing
vector populations and proportion of viruliferous vector. However, high levels of vector
population do not always result in high incidence of RTD. Dispersal of plant viruses by
insects is also affected by other biological factors such as the number of virus inoculum
sources, the number and activity of viruliferous insects, the readiness for insect to
become viruliferous, the length of time for which the insect remains viruliferous, and the
susceptibility of host plants (Lapis, 1991).
Cultural practices adapted by farmers often influence RTD epidemics. Multiple
rice cropping over large areas provides a continuous source of plant hosts and enables the
year-round development of insect pests such as GLH, plant hopper, stem borer, and leaf
holder (Litsinger, 1989). The planting of single cultivar in the field often triggers the
13

apid progress of disease infection. Other adjustable cultivation practices like crop
spacing and transplanting timing also may affect the level of RTD. The rate of disease
spread was slower in closer spacing than under wider spacing (Shukla and Anjaneyulu,
1981b and 1981c). In an asynchronously planted field, RTD at harvest correlated
positively with the incidence at 6-10 weeks after transplanting (Hasanuddin et al. 1999).
The result of Savary et al. (1993) showed that the low RTD incidence was associated
with either very early or very late planting, whereas high RTD incidence was associated
with intermediate planting. Meanwhile, the studies of Chancellor et al. (1996) showed
that RTD incidence was much higher in late plantings than in early plantings.
Disease Management
The occurrence of RTD tends to be more serious in areas where farmers adopt
asynchronous and continuous cropping pattern. Although the incidence of RTD can be
managed to a certain level by various cultural practices to disrupt the disease cycle
(Othman et al. 1999; Sama et al. 1991), the deployment of varieties resistant against
tungro viruses has been considered most effective (Koganezawa and Cabunagan, 1997).
Under field condition the cause of RTD is not easily observable and the disease is
difficult to predict and control. Hence farmers regarded RTD as a serious threat in rice
production, even in areas without much experience of RTD outbreaks. The use of
resistance varieties and the application of pesticides to control the insect vectors believed
to carry tungro viruses are most common control measures among farmers (Warburton et
14

al. 1996). However, the complex nature of RTD and the unpredictability of its outbreak
have presented farmers with difficult control decisions, compounded by the absence of
reliable disease management strategies (Chancellor, 1996).
Cultural control such as synchronized cropping, and planting time adjustment are
some of the methods that have been recommended to prevent the incidence of RTD
Though these approaches have an important role in the disease management, there are
some limitations as to their use, for instance synchronized cropping is very difficult to
implement due to difficulty in water control and labor shortage. The choice of appropriate
planting time when vector population is low also seems to be not applicable due to a shift
in the pattern of vector population growth that was observed in Indonesia following a
change in planting dates (Sama et al. 1991).
Unlike fungal pathogens or insect pests, there is virtually no chemical treatment for
RTD since viruses rely heavily on host components for their multiplication, thus any
chemical treatment with antiviral activity would be likely to have anti-host activity as
well (Fraser, 2000). Hence chemical treatment in RTD control is directed mainly to insect
vectors. However, this approach often may not be effective because of the time lapse
between the insecticide application and the eradication of vectors from field, which may
give the vectors enough time to transmit the viruses. Besides, farmers in developing
countries usually can hardly afford pesticides, and the application of any insecticide is not
a sound choice due to ecological concerns. There is, therefore, a continued interest for
natural resistance since it is an affordable yet efficient way to fight diseases (Keller et al.
2000).
15

Resistance to virus in plants could be considered as a form of biological control
since it involves various biological interactions between host plants and infecting viruses.
The resistance may operate hypothetically, when it interferes in any steps of viral
pathogenesis: inhibition of infection establishment, suppression of replication (Keller et
al. 1998), blockage of virus movement and transport (Albar et al. 2003; Carrington et al.
1996), and suppression of symptom expression (Fraser, 1990; Hull, 2002; Valkonen,
2002). In RTD pathosystem, the target of resistance may be vector, RTBV, RTSV, or
their combinations.
Use of resistant variety is one of the most important and economical components
of RTD management strategy. Plant breeders have long recognized the need for varieties
resistant to RTD and its vectors, For example, most breeding lines of rice produced in
IRRI since 1969 had at least one parent with resistance to GLH. Therefore, all varieties
developed in IRRI except IR20 are rated as having GLH resistance at the time of release
(Khush et al. 2004). The major donors of the GLH resistance trait were Ptb 18, Gam Pai
30-12-15, and Ptb 33. Such rice cultivars show adequate resistance to the vector and may
be able to escape RTD in the field under light to moderate disease pressure (Hibino and
Cabauatan, 1987). The vector resistant varieties helped to minimize yield losses that are
likely to have occurred because of RTD. Despite such efforts, the breakdown of vector
resistance was often observed after a few consecutive seasons of intensive cultivation of
formerly resistant varieties (Dahal et al. 1990a), indicating that resistance to the vector
may not be durable. Therefore it is rather desirable to combine vector and virus resistance
to confer durable resistance to RTD on plants.
16

Resistance to Rice Tungro Viurses
During 1980s, a change in the strategy for development of RTD resistant varieties
was made to incorporate resistance to the viruses in addition to GLH resistance. Although
the sources for complete resistance to RTBV have not been found in rice germplasm,
several varieties were found to be tolerant to RTBV (Imbe et al. 1995; Cabunagan et al.
1996). Tolerant varieties can have lesser degree of symptom expression, while allowing
virus to multiply and spread (Fraser, 2000). Cultivars originating from Indonesia such as
Balimau Putih and Utri Merah express mild symptoms when infected with both RTBV
and RTSV (Hasunuddin and Hibino, 1989). It was reported that 3 accessions each of wild
rice species O. rufipogon and O. officinalis, and 1 accession of O. ridleyi were tolerant to
RTBV infection, and the tolerance dose not seem to depend on vector resistance. These
wild rice species have been considered as useful resources for developing RTD resistant
variety (Kobayashi et al. 1993). Cytological study indicated that the number of cells
infected with RTBV or RTSV was found to be less in these tolerant cultivars/species than
in an RTD susceptible variety Taichung Native 1 (TN1). The tolerance in these varieties
as observed having low concentration of RTBV could be attributed to fewer susceptible
cells and lower levels of RTBV multiplication. Breeding for tolerance which may reduce
yield loss under severe infection pressure is important in RTD management. When
tolerance to RTBV is integrated with RTSV resistance, it might become an ideal solution
to control for RTD (Anjaneyulu, 1996).
17

Many IRGC accessions have been reported as resistant to RTSV infection (Hibino
et al. 1990; Koganezawa and Cabunagan, 1997). RTSV is important because it is
required for the transmission by leafhopper vectors of RTBV (Hibino et al. 1979; Hibino
and Cabunagan, 1986). RTSV could occur as an independent disease (Bajet et al. 1986)
and capable of causing yield loss of as much as 40% on susceptible varieties (Hasanuddin
and Hibino, 1989). The deployment of varieties with RTSV resistance is likely to have a
significant effect in the reduction of RTD spread as suggested by Hibino et al. (1988) and
subsequently demonstrated by Cabunagan et al. (1990), and Satapathy, et al. (1997).
RTD infections in RTSV resistant IR26 were at random whereas, it occurs in patches in
RTSV susceptible IR64.
Varietal Mixtures as RTD Management Option
New approaches and strategies that are more effective and durable than those now
available are needed so that crop stands may acquire some of the stability and resistance
of natural vegetation (Thresh, 1982). Host needs to be diverse particularly in the form of
mixtures (Wolfe et al. 1981) so that they could withstand the pressure from virus
genotype with matching virulence (Thresh, 1982).
Wolfe (1985) has reviewed the importance of diversity (multilines and mixtures)
for controlling diseases of economic plants and Browning (1989) has established a clear
rationale for the use of diversity for controlling disease.
18

Recently, host diversity is gaining attention worldwide specially its long term
effect in managing cereal disease. One important factor in using genotype mixture of
agricultural crops is to attempt to reduce the selection pressure for pathogens that can
overcome valuable forms of disease resistance in crop plants (Garrett and Mundt, 1999).
Further, a group of crop species at scattered sites may restrict the build-up of pests and
diseases and enable the crop to escape severe damage (Harlan, 1976). It may also reduce
the risk of yield loss caused by abiotic and biotic stress by taking advantage of yield
compensation occurring in mixtures grown in variable environments (Mundt, 1999).
With most obligate pathogens, disease was less in mixtures than the mean of their
components in monoculture (Smithson et al. 1996). The decrease in powdery mildew
(Erysiphe graminis f. sp. hordei) severity in barley mixtures over their component means
ranged from 8.9% to 80% (Kolster et al. 1989), the decrease in stripe rust (Puccinia
striiformis) severity in wheat mixtures over their component means ranged from 13% to
97% (Finckh and Mundt, 1992), the decrease in blast (Pyricularia oryzae) severity in rice
mixtures ranged from 50% (Chin et al., 1982) to 66% (Bonman et al. 1986), and the
decrease in the severity of several bean diseases including rust (Uromyces
appendiculatus), angular leaf spot (Phaseoisariopsis griseola), anthracnose
(Colletotrichum lindemuthianum) and halo-blight (Pseudomonas syringae pv.
phaseolicola) in bean mixtures over their components reached 50%, 12.3%, 6.8% and
16.4%, respectively (Mundt and Leonard, 1986; Pyndji and Trutmann, 1992).
Successful genetic diversification experiment was conducted in China. The result
showed that the infection of the highly susceptible glutinous rice varieties, Huangkenuo
19

and Zinuo, with blast was significantly reduced when inter-planted with the generally
resistant indica hybrid varieties, Xianyou 63 or Xianyou 22 (Zhu et al., 2000).
Much effort has been made to investigate mixed cropping systems, especially with
respect to the ecological processes involved in crop performance (Geno and Geno, 2001).
The relation between crop or cultivar mixtures and disease severity has been investigated
extensively, but has focused mostly on disease caused by windborne pathogens and foliar
pathogens of small grains (Mundt, 2002). Effects of mixed cropping on soilborne
pathogens have been described less frequently (Abadie et al. 1998; Autrique and Pots,
1987). For example, Burdon and Chilvers (1976) showed reduced spread of Pythium sp.
in a garden cress–ryegrass mixture and Vilich (1993) reported a reduction in disease
severity of soilborne pathogens in barley–wheat mixtures. In these experiments, disease
suppression was investigated for pathogens specific to one or both of the crops included
in the mixed cropping. Study on the effect of mixed cropping for the soilborne diseases
(non-specific pathogen) was conducted by Hiddink et al. (2005). Their results showed
that mixed cropping of soil with Brussels sprouts and barley or with triticale and white
clover did not enhance disease suppression of soil to three soil-borne diseases
Rhizoctonia solani, Fusarium oxysporum f. sp. lini, and Gaeumannomyces graminis var.
tritici.
While the mixtures of diverse hosts appeared effective in disease control, the
mechanisms of disease reduction are still largely unclear (Burdon et al. 1980). It was
suggested that the barrier effects of resistant plants (Trenbath, 1977) and the reduction in
20

density of susceptible plants per se (Brown, 1975) might contribute to the disease
suppression in variety mixtures.
Garrett and Mundt (1999) stressed that host-diversity effects could be influenced
by the spatial pattern of initial inoculum. Even if a susceptible variety were present, the
spread of a disease was slow when an initial inoculum was likewise low. Studies on
Puccinia coronata on oats showed that mixtures of large sizes of hosts of the same
genotypes can produce a large decrease in disease when the disease was focally
distributed. This suggests that the disease spreads from a small number of inoculum
sources rather than from those more evenly dispersed throughout fields at the beginning
of an epidemic (Mundt and Browning, 1985; Mundt and Leonard, 1985).
Wolfe (1984) noted that resistant plants interfere with the movement of inoculum
between susceptible individuals, and that induced resistance or cross-protection may also
reduce disease development. Burdon (1987) explained that mixing of individuals with
different levels of resistance initiates a complex series of interconnected changes which
affect the ability of pathogens to survive and reproduce and, in consequence, disease
development.
There have been very few studies regarding the effects of variety mixtures on
diseases caused by viruses. The outcome of mixtures on viral diseases may be
complicated by the level of abundance and the behavior characteristics of vector, since
these usually greatly affect the efficacy of the transmission the pathogen (Power, 1990).
Power (1991) found that a 1:1 mixture of a susceptible and resistant oat (Avena
sativa) cultivars reduced the incidence of yellow dwarf to approximately the level
21

observed in the resistant component for all three years of the study. The incidence of
wheat soil-borne mosaic virus was reduced by 33.2 and 39.8%, respectively, in 1:1 and
1:3 mixtures of susceptible and resistant winter cultivars. Under field condition, the
resistant cultivar did not produce viruliferous zoospores of the soil-borne vector (Hariri et
al. 2001). Therefore, the presence of the resistant cultivar in the mixture may have
reduced virus transmission between susceptible plants in the mixture (Mundt, 2002).
Homogeneous planting of cultivars which may have resistance against viruses and
vectors over large areas could facilitate them to adapt to such cultivars more easily.
Consequently, the use of heterogeneous crop populations was proposed and eventually
practiced. Diversity in such heterogeneous environment has been considered to be an
essential characteristic promoting balanced polymorphism in natural ecosystems
(Browning, 1974). Although the use of resistant varieties is obviously preferred, the
effectiveness may decline after continuous use (Truong et al. 1999). The genetic
uniformity of varieties is very crucial in the development of RTD epidemics (Chin and
Wolfe, 1981), since it is highly likely that crop stands that contain more than one species
of plant affect virus spread. The mixing of crops containing those that are not compatible
to viruses and vectors prevalent in the area may allow virus to spread more slowly in such
mixed crops than in single crop species (Gibbs and Harrison, 1976). Aphids in cultivar
mixtures showed higher movement rates and shorter tenure times than aphids in pure
stands. This may have reduced transmission rates for this virus, because an aphid must
feed for several hours to inoculate a host plant (Power, 1991).
22

Besides their effect in controlling diseases, mixtures have been shown to stabilize
and sometimes increase yields (Finckh and Wolfe, 1997). In the U.S., more than 100,000
hectares of wheat cultivar mixtures are grown for protection against yield losses and to
increase yield stability in general (Finckh et al. 1999). Variety mixtures help to buffer the
system against a range of environmental stresses and show highly stable yield (Chin and
Husin, 1982). The experiments on blast by Ashizawa et al. (1999) and Bonman et al.,
(1986) showed that yields of mixtures were larger than the means of pure stands and the
yield increase due to mixing was high under severe epidemic. A mixed population
provided guaranteed yield.
Importance of Farmers’ Perception Survey
Technology is one of the resources for agricultural production and alleviates
various physical, economic and social constraints. It can be reached by farmers through
technology transfer. Technology transfer refers to the general process of moving
information and skills from information or knowledge generators such as research
laboratories and universities to clients such as farmers (Bozeman, 2000). The outcome of
new technology transfer depends on the farmers’ adoption and willingness to bring this
into practice, and further diffusion into the community. Therefore, it is important to know
how farmers perceive newly developed technologies for better understanding of factors
affecting their decision to adopt or not. Perception acts as a filter through which new
23

observations are interpreted. The farmer’s choice of action will depend on his evaluation
of the technology in terms of his own personal perspective.
If scientists have to work with farmers to improve crop production and crop
protection, they should recognize farmers’ constraints and their existing technical
knowledge (Kenmore, 1991). Farmers in developing countries have substantial difficulty
in managing plant diseases, since their understanding of disease processes is limited.
Consequently disease management in developing countries is more often likely to be
ineffective (Nagaraju et al. 2002; Nelson et al. 2001; Bentley and Thiele, 1999).
A farmer survey is an important process to gather data necessary to assess the
needs of intended beneficiaries, their knowledge level and perceptions for problems, their
constraints in dealing with the problem, and their attitudes and practices to manage the
problems (Escalada and Heong, 1997). Meanwhile farmer’s depth of knowledge about
pests is related to the importance and visibility of the pest, because pathogens are not
usually easily seen, thus it is difficult for farmers to account for the causes of diseases
(Bentley and Thiele, 1999).
In a survey conducted by Warburton et al. (1997) they found out that, farmers in
the Philippines are aware that varieties have differing resistance or susceptibility to RTD
and majority would change to another variety to prevent RTD from occurring again. In
“hotspot” areas or in areas that experience outbreak of RTD farmers give importance to
variety resistance and is used as one of the criteria for selection of varieties to plant. But
most farmers are not aware that continuous planting of resistant varieties, especially those
24

esistant to vectors may results in the breakdown of their resistance (Dahal et al. 1990a)
and the emergence of new strains of tungro viruses (Cabauatan et al. 1995).
Farmers’ Preference for Grain Quality
IR64 released by IRRI in 1985 is preferred among the farmers, millers and
consumers in the Philippines because of its good eating and milling qualities (Khush and
Virk, 2005), however, this variety is highly susceptible to RTD and not recommended for
planting in RTD endemic areas of the Philippines since 1994 (Anonymous, 1994).
Rice is normally consumed after it has been milled and cooked without
undergoing any other processing that could improve quality. While millers prefer
varieties with high milling and head-rice recovery, consumers prefer varieties with good
eating quality. As in other countries where rice is grown and consumed, in the Philippines
consumer acceptance determine the commercial success of a newly released variety
(Merca et al. 1978).
Grain quality includes not only the traditional physical and visual properties of the
rice grain but also cooked rice texture as indexed by apparent amylose content, alkali
spreading value (index of gelatinization temperature), gel consistency, actual texture
measurement of cooked grain and protein content (nutritional value) (Juliano and
Duff,1991).
25

Plant Materials
MATERIALS AND METHODS
Two test varieties Matatag 9 (IR73885-1-4-3-2-1-6) released by IRRI as a stop
gap rice tungro disease (RTD) resistant variety in the Philippines in 2002 (Khush et al.
2004), and IR64 (IR18348-36-3-3, released in 1985) which is susceptible to RTD and
only tolerant to green leafhopper (GLH) were used in this study. Taichung Native1 (TN1)
and IR62 (IR13525-43-2-3-1-3-2, released in 1984) were used as susceptible and resistant
check varieties, respectively.
Insect Vector
The colony of GLH was maintained on susceptible variety, TN1 in 55 x 55 x 25 cm
metal cages. Plants of TN1 (25 to 35-day old) were used for feeding and egg laying up to
the adult stage of the insects. To generate the new population, the insects were introduced
into the insect cage containing pots of feeding plants and left there for two days to allow
them to lay eggs. Then the plants were transferred to other cages for egg incubation and
nymph hatching. Supply of fresh feeding plants to these cages was done every other day.
Viruliferous GLH were prepared from newly emerged population by feeding on plants
infected with RTSV/RTBV for 4 days.

Viruses
Inocula for RTSV and RTBV were maintained by successive transmission of
viruses in TN1. Source plants were tested for the presence of RTSV and RTBV by
ELISA before acquisition feeding access by GLH.
Assay Procedure for RTBV and RTSV Infection
Inoculated plants were evaluated for infection with RTBV or RTSV by ELISA
(Bajet et al. 1985 and Cabunagan et al. 1993) using IgG antibody purified from
polyclonal antisera to purified RTBV or RTSV (Cabauatan and Hibino, 1988). Polyvinyl
chloride microtiter plates (96-well, flat-bottomed, Becton Dickinson Labware, USA)
were coated separately each with 95µl of 0.05 M sodium carbonate coating buffer (pH
9.6) containing 1.5µg/ml of IgG against RTBV or RTSV. The IgG-coated plates were
incubated at 37 ◦ C for 3-4 hours. The plates were then washed using 0.02M phosphate
buffer (pH 7.4) containing 0.15M NaCl and 0.05% Tween 20 (PBS-T) 6 times for 5 min
each. Leaf samples were homogenized in PBS-T at 1:10 sap dilution using a leaf and bud
press apparatus (Erich Pollahne), then 95µl sap from each sample was loaded into each
well of the microtiter plate. The plates were incubated at 4 ◦ C overnight and then washed
using PBS-T as described above. Extracts from healthy plants and RTD infected plants
were used as negative and positive controls, respectively. Ninety five µl of alkaline
phosphatase conjugated-IgG in PBS-T (1 μg/ml) was added to the wells, incubated at
27

37◦C for 3–4 h, and then washed using PBS-T. Ninety five µl of ρ-nitrophenyl phosphate
(Sigma, USA) at 1 mg/ml in 10% diethanolamine was added to each well. Color reaction
was allowed to take place for 30 minutes. The presence of RTBV or RTSV in leaf
extracts was determined by measurement of the absorbance at 405 nm using an ELISA
reader (BOSCH, Germany). Samples with absorbance values at 405 nm greater than 0.1
were considered positive for RTBV or RTSV infection.
Forced Test Tube Inoculation
Biological Characterization of Resistance to
Rice Tungro Disease in Matatag 9
Forty 6-day old seedlings each of Matatag 9, IR64, and TN1 were used per
treatment. Each seedling was placed in a test tube (18 mm x 150 mm) with cap
containing small amount of water. The viruliferous GLH (1, 3, or 5 per tube) was
introduced into the test tube and was confined for 24 hours. Inoculated seedlings were
transplanted at 5 seedlings per pot and maintained in the greenhouse. Two youngest
leaves were collected from each plant at 21 days after inoculation (DAI) for ELISA to
evaluate the presence of viruses. The infection rates with virus were calculated using the
following equation:
Infection rate (%) = 100 x (Number of infected seedlings/number of inoculated seedlings)
28

The experiment was repeated three times, and the rates of plants infected with
RTBV, RTSV, and both RTSV and RTBV were calculated.
Relative Quantification of RTBV and RTSV
Preparation of samples. Three viruliferous GLH were introduced into each test
tube containing a 6-day old seedling of Matatag 9 or IR64. GLH was allowed to feed on
the seedlings for 24 hours. Inoculated seedlings were transplanted at 5 seedlings per pot
and maintained in the greenhouse. Two youngest leaves per seedling were collected from
20 plants per variety at 7, 14, 21, 28, 35, 42, and 49 DAI. All plants from which leaves
are collected were kept until 60 DAI. At 60 DAI, two youngest leaves were collected
again from each plant for ELISA to determine the presence of viruses.
Optimum assay condition. In order to determine the optimum dilution rate for
quantitative ELISA of tungro viruses, serially diluted extract from TN1 (internal control)
Matatag 9, and IR64 infected with RTBV and RTSV were tested for their reactivity with
antibody against tungro viruses. Sap samples were prepared from the leaves of 5
individual plants of Matatag 9 and IR64 collected at 21 DAI. Each sample was diluted
with extraction buffer at 10X, 20X, 30X, 50X, 100X, 200X, 400X, and 800X with three
replications and 95 µl of diluted sap was placed into the wells of an ELISA plate. Each
plate also included internal control samples diluted at 10, 50, 100, 200 and 400X. The
absorbance at 405 nm of each sample was read at 15, 30, 45 and 60 min after addition of
29

the enzyme substrate. The average absorbance value from 5 samples with 3 replications /
variety for each dilution rate was calculated and the optimum condition was determined.
Characterization of virus replication. Samples collected from the leaves of 20
plants per variety at 7, 14, 21, 28, 35, 42, and 49 DAI were tested by ELISA at 10X and
the optimum dilution to evaluate the relative accumulation levels of RTSV and RTBV.
ELISA reading was done at 15, 30, 45 and 60 min after addition of the enzyme substrate.
Samples from leaves of plants at 60 DAI were tested by ELISA at 10X dilution to
determine actual infection rate of plants with the respective viruses.
Biological Characterization of Matatag 9
Resistance to Green Leafhopper
GLH Preference and Tungro Viruses Transmission
Pre-germinated seeds of Matatag 9 and IR64 were planted in 12-cm diameter pots
with 5 seedlings per pot. Ten-day old seedlings were used for inoculation. Two pots, one
planted with IR64 and another with Matatag 9 were placed together inside a plastic cage
(Fig. 1). Inoculation was conducted inside the cage by introducing approximately 50
viruliferous GLH from the center top of the plastic cage. The number of GLH that
alighted on each potted plant was counted 0.5, 4, 8 and 24 hours after release. The
counting of GLH was replicated 20 times. Insects were removed 24 hours after
30

infestation from the test plants and the inoculated plants were maintained in the
greenhouse.
The number of alighted GLH were analyzed by Chi-square test to determine
whether observed ratios of GLH attracted to resistant and susceptible plants deviated
significantly from the no preference ratio of 1:1. Infection rates of tungro viruses were
evaluated at 21 DAI by ELISA. Correlations between the number of alighted GLH and
the infection rates for RTBV, RTSV and both RTBV and RTSV, from each variety were
examined.
Fig. 1. Experimental set-up for settling preference test. Five 10-day old seedlings each of
Matatag 9 and IR64 planted in separate pots were placed inside a plastic cage.
31

Adult GLH Longevity
Twenty 6-day old seedlings each of Matatag 9, IR64, TN1 and IR62 were
prepared. Each seedling was placed in a test tube with nylon mesh top. Ten newly
emerged adult GLH of each sex were prepared for each test variety. Insects were
introduced singly into the test tubes. Seedling was replaced whenever it showed severe
necrosis. The longevity of GLH was taken as the number of days when the insect was
found alive. This experiment was established in split-plot design with 3 replications.
Mean of longevity was calculated for the 10 insects of each sex introduced into each
variety using the following equation:
Mean of Longevity = Total number of days that 10 insects live on each test variety/10
Data analysis was done by the least significant difference (LSD) test for the
means, and by the balanced analysis of variance (BAOV) included in IRRISTAT to
evaluate the significances among varieties and between GLH sexes.
Nymphal Mortality
Ten 6-day old seedlings each of Matatag 9, IR64, TN1 and IR62 were singly
placed in a test tube. Ten 2 nd -instar nymphs of GLH were then introduced into each of the
tubes. The mouth of the test tube was closed with fine-mesh nylon screen for proper
32

ventilation. The experiment was established in randomized complete block design
(RCBD) with 3 replications. The standard number of GLH (number of live insects) was
counted at 6 hrs after infestation. Three days after infestation, the mortality of the GLH
nymphs in each test tube was calculated using following equation, and mortality of the
nymphs in all test tubes of each test material was averaged and used as the antibiosis
rating.
Mortality (%) = 100x (Number of insects that survived/ Standard number)
Data analysis was done by the LSD test and BAOV to evaluate the significances
among varieties.
Growth and Development of GLH Nymph
Pre-germinated seeds of Matatag 9, IR64, TN1 and IR62 were singly sown in a
pot (12 cm in diameter) covered with 10 x 60-cm cylindrical mylar cage with fine-mesh
nylon screen top and side windows. Five 2 nd -instar GLH were introduced into the cage at
21 days after sowing. The experiment was established in RCBD with 20 replications.
Growth was measured by counting the number of nymphs that became adults and the
time taken to reach the adult stage. The insect growth index for each variety was
calculated as the ratio of the percentage nymphs becoming adults to the mean growth
33

period in days (Saxena et al. 1974). Data analysis was done by the LSD test, and BAOV
to evaluate the significances among varieties.
Fig. 2. Experimental set-up for the test for growth and development of GLH nymph.
34

Performance Evaluation of Varietal Mixture Components
Comparative Morphological and Yield
Characteristics of Matatag 9 and IR64
Forty seeds each of Matatag 9 and IR64 were prepared. Six day-old seedling of
Matatag 9 or IR64 was singly transplanted at 20cm x 20cm distance between plants with
4 x 10 arrangements in the screenhouse. The condition for soil nutrition and soil water
content was maintained uniform during the experiment. Height was measured at 15, 30,
45, 60, 75, and 90 days after transplanting (DAT). Number of tillers was counted at 30
and 60 DAT. Number of days to flowering and maturity were recorded. Final height from
the bottom to top of longest panicles was measured at harvest time. Data on yield
parameters such as number of productive tillers, panicle length, number of filled grain per
panicle, grain size (width and length) and thousand grains weight (TGW) were obtained
after harvest. The measurement of each yield parameter was done as follows:
• Panicle length: 5 panicles per plant were measured
• Number of filled grains per panicle: unfilled and filled grains from 3 panicles were
counted.
• Grain size: the width and the length of 100 hulled grains and 100 dehulled grains were
measured.
• Weight of 1000 grains: 1000 hulled grains and 1000 dehulled grains were weighed.
This measurement was repeated five times.
35

Data from each parameter were analyzed by BAOV and the LSD test. Plants at
the outer row of the plot were excluded for data analysis.
Effect of Mixed Planting of Resistant and
Susceptible Varieties on the Incidence of Rice Tungro Disease
For the mixture treatments, seeds of the test varieties of Matatag 9 and IR64 were
mixed thoroughly as shown in Table 1.
Table 1. Ratios of seed mixtures used for mixed variety planting.
TREATMENTS
PERCENTAGE IN MIXTURE
Matatag 9 IR64
T1- (Pure stand Matatag 9) 100 0
T2- (Mixture) 75 25
T3- (Mixture) 50 50
T4- (Mixture) 25 75
T5- (Pure stand IR64) 0 100
Tray Inoculation and Experimental Design
Seeds were soaked overnight. Pre-germinated seeds were sown in a plastic tray
(49cm x 37cm x 12.5cm) with 16 columns and 25 seeds per column. When seedlings
were 10-days-old, the tray was placed inside a cage to inoculate plants with 3 or 10
viruliferous GLH per seedling. GLH was allowed to feed on the seedling for 4 hours. All
inoculations were conducted at the same time. Two leaves per plant were collected at 21
36

DAI and checked for the presence of RTSV and RTBV by ELISA. The experiment was
established in Split-Plot design with 3 replications.
Mixed Seed Planting Layout
Five different seed mixtures were prepared as treatment (Table 1). One tray was
used per treatment. Twenty-five pre-germinated seeds were planted in columns 1 to 16.
Fig. 3 shows an example of the planting layout for T2 (75:25 of Matatag 9 and IR64)
mixture.
37

R
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Column
Fig. 3. Example of seed layout of T2 (75:25 for Matatag 9 and IR64) seed
mixtures for tray inoculation: R indicates position of resistant variety,
Matatag 9 and S indicates position of susceptible variety, IR64.
S
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38

Interplanting (row mixture) Layout
For T1 and T5 only Matatag 9 or IR64 was planted in all columns in a tray. For
T2 mixture, every fourth column (e.g. columns 4, 8, 12, and 16) was planted with IR64,
the rest were planted with Matatag 9 (Fig. 4). For T3 mixture, every second column (e.g.
columns 2, 4, 6, 8, 10, 12, 14, and 16) was planted with IR64, the rest were planted with
Matatag 9 (Fig. 5). For T4 mixture, columns 2, 3, 4, 6, 7, 8, 10, 11, 12, 14, 15, and 16
were planted with IR64, the rest were planted with Matatag 9 (Fig. 6).
R
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Fig. 4. Seed layout of T2 mixture. R indicates position of resistant variety,
Matatag 9 and S indicates position of susceptible variety, IR64.
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40
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Fig. 5. Seed layout of T3 mixture. R indicates position of resistant
variety, Matatag 9 and S indicates position of susceptible variety, IR64.

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Fig. 6. Seed layout of T4 mixture. R indicates position of resistant variety,
Matatag 9 and S indicates position of susceptible variety, IR64.
Rates of plants infected with RTBV, RTSV and both RTSV and RTBV were
obtained from the respective treatments. Mixture effects on disease incidence were
evaluated by the LSD test and BAOV in split plot design.
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41

Serial Inoculation in Resistant and Susceptible Varieties
Six-day old seedlings of test materials were placed individually in test tubes and
single viruliferous GLH was introduced and allowed to feed for 24 hours, then transferred
to next rice seedling as scheduled in Table 2. The serial transmission was continued for 5
days. Inoculated seedlings were transplanted at 5 seedlings per pot and maintained in the
greenhouse. The infection rates of tungro viruses were evaluated at 21 DAI by ELISA.
Table 2. Combination of Matatag 9 and IR 64 for serial transmission
COMBIATION (C) 1 st DAY 2 nd DAY 3 rd DAY 4 th DAY 5 th DAY
C.1 Matatag 9 Matatag 9 Matatag 9 Matatag 9 Matatag 9
C.2 IR64 Matatag 9 IR64 Matatag 9 IR64
C.3 Matatag 9 IR64 Matatag 9 IR64 Matatag 9
C.4 IR64 IR64 IR64 IR64 IR64
42

Farmers’ Perception Survey on the Use of Mixed Planting
Survey site description. The survey site was in Barangay Progreso of the Ajuy
Municipality in the northeast part of the province of Iloilo, Philippines (Fig. 7). Ajuy is a
4 th class municipality consisting of 34 barangays. Ajuy has a total land area of 19,432 ha
and 15,042 ha is agricultural land.
Survey procedure. A mini-survey by means of a questionnaire was conducted
during the farmers’ forum on “Rice Tungro Disease Management” in Barangay Progreso,
September, 2005. The half-day forum aimed to discuss with the farmers through
exchanges of ideas and knowledge on RTD and its management and to introduce the new
concept of varietal mixture for RTD management.
The questionnaire used in the survey was almost the same as that used by
Warburton et al. (1997) in a comprehensive survey of farmer’s perception about tungro in
the Philippines. The only difference was that some questions were added to elicit
farmers’ perception on the use of variety mixture as a management option for RTD. The
questionnaire (Appendix 1) was distributed to about 50 randomly selected farmers who
are the members of the irrigator association in Ajuy, Iloilo. Respondents were first
requested to fill up the questionnaires by themselves with a guidance of the Chief Officer
of Research and Institutional Development (RAID) as needed.
Questionnaire was aimed to evaluate the farmers’ socio-demographic
characteristic, farming structure, perceptions of biotic constraints upon rice production,
43

awareness of RTD and its control, and awareness of mixed variety planting. For each
question, the percentage of farmers who gave the same answer was calculated. Those
who did not respond to certain questions were excluded from the calculations. In cases
where multiple responses were obtained, total sample size (52 farmers) was used.
Fig. 7. The site (shaded red) of the survey in the municipality of Ajuy, Iloilo Province,
Philippines
44

Grain Quality Evaluation of Mixed Seed Planting
Rice grains. The rice grains used for evaluation were obtained from the crops
grown during the dry season (DS) 2005 crop in Midsayap, Cotabato. The grains were
sun-dried to 14% moisture content. About 1000 grams seeds were collected from the
different treatments as shown in Table 1 for grain quality evaluation at the Grain Quality
and Nutrition Research Center (GQNRC) in IRRI.
Milling quality. About 125 gm of rough rice grains (paddy rice) were used for
milling quality determinations. Rough rice grains were dehulled with a Satake Laboratory
Sheller in two passes. The resulting brown rice was weighed to get the percentage of
hulls. The brown rice was milled in a MacGill Mill Number 2 for 30 seconds with the
prescribed added weight (680 gm) on the pressure cover, followed by a second milling
for another 30 seconds without the weight. About 13-14% of the outer layer of brown rice
was removed through the milling process. The milled rice sample was collected in a jar or
thick paper bag and sealed immediately. The rice was allowed to cool before weighing to
minimize grain cracking during cooling. The weight of the total milled rice was recorded.
Whole grains (head rice) were separated from the total milled rice with a rice-
sizing device. The indentation size of the device depends on the grain size. Two plates
of the same size were used for each run. The resulting head rice was weighed. The
percentage of hulls of rough rice was calculated as follows:
45

Brown Rice (%) = Weight of brown rice x 100
Weight of rough rice
Total Milled Rice (%) = Weight of total milled rice x 100
Weight of rough rice
Head Rice (%) = Weight of head rice x 100
Weight of rough rice
Grain size, shape and appearance. Length, width and percent chalkiness of
milled rice were determined using the Cervitec 1625 Grain Inspector (Foss Tecator,
Sweden) from five to ten grams sample of milled rice. Table 3-a and -b are the
classification criteria used for evaluation. The obtained percentage of chalkiness was
classified into five levels 1: 0-10%, 2: 10-25%, 3: 25-50%, 4: 50-75% and 5: >75%.
Table 3-a. Classification for grain size
SCALE SIZE CATEGORY LENGTH (mm)
1 Very long More than 7.50
3 Long 6.61 < 7.50
5 Medium or intermedium 5.51 < 6.61
7 Short Less than 5.51
Table 3-b. Classification for grain shape
SCALE SHAPE LENGTH/WIDTH RATIO
1 Slender Over 3.0
5 Medium 2.1 to 3.0
9 Bold 2.0 or less then 2.0
46

Amylose content. The simplified procedure of Juliano (1971) was used for the
amylose content analysis. Rice varieties were grouped on the basis of their amylose
content into waxy (0-2%), very low (3-9%), low (10-19%), intermediate (20-25%) and
high (>25%).
Gelatinization temperature (GT). The alkali digestibility test (Little et al. 1958)
was used for estimating gelatinization temperature. Six grains of milled rice were
incubated in 10 ml of 1.7% (0.3035 N) KOH at room temperature or 30°C for 23 hours
and the degree of spreading was assessed according to the seven-point scale as shown in
Table 4.
Table 4. Numerical scale for gelatinization temperature (GT).
Score Spreading Alkali digestion GT
1 Kernel not affected Low High
2 Kernel swollen Low High
3 Kernel swollen; Collar complete or narrow Low or Intermediate High-intermediate
4 Kernel swollen; Collar complete and wide Intermediate Intermediate
5
Kernel split or segregated; Collar complete and
wide Intermediate Intermediate
6 Kernel dispersed; Merging with collar High Low
7 Kernel completely dispersed and intermingled High Low
Gel consistency. The pasting properties of milled rice were measured with a
Rapid Visco Analyser RVA-4 (Newport Scientific, Sydney, Australia) according to the
procedure of Cagampang et al. (1973). Rice flour (3 gm) was weighed directly into the
aluminum RVA canister and mixed with 25ml of distilled water. The sample was held at
47

50 °C for 1 min, heated to 95 °C at a rate of 12 °C/min (i.e. in 3.75 min), held at 95 °C
for 2.5 min, cooled to 50 °C at a rate of 12 °C/min and held at 50 °C for 2.5 min. Based
on the results rice grains were categorized into three as follows:
1. Very flaky rice with hard gel consistency (length of gel, 40 mm or less);
2. Flaky rice with medium gel consistency (length of gel, 41 to 60 mm); and
3. Soft rice with soft gel consistency (length of gel, more than 61 mm).
48

Rates of Infection with RTSV and RTBV
under Different Inoculum Levels
RESULTS AND DISCUSSION
Biological Characterization of Matatag 9
Resistance to Rice Tungro Disease
Less than 20% of Matatag 9 was infected with RTBV at 1 viruliferous GLH per
seedling, whereas higher infections were observed in IR64 (58.5%) and TN1 (85.0%)
(Fig. 8). For each test variety higher rates of infection with RTBV was observed with
increased insect numbers and the infection rates between Matatag 9 and IR64 were
considerably different. TN1 consistently showed highest infection. The rates of infection
with RTSV, however, were considerably low compared to those with RTBV for all test
varieties irrespective of the number of insects used for inoculation. The RTSV infection
was higher in IR64 than in Matatag 9.
Temporal Change in Apparent Rates of
Infection with RTSV and RTBV
The rates of RTBV infection were higher in IR64 than in Matatag 9 regardless of
the time of sampling, although the rate of infection with RTBV in Matatag 9 inoculated at

Fig. 8. Infection rate of RTBV and RTSV in three varieties with 1, 3, and 5 viruliferous
GLH by the forced test tube inoculation.
50

6-days old is still considerably high (Table 5). RTBV infection rates at 60 DAI in
Matatag 9 and IR64 inoculated at 6-days old were not much different from those
examined at the time of initial sampling (Table 5). Mean RTSV infection rates in IR64
and Matatag 9 inoculated at 6-days old were 70 and 26.4% at time of initial sampling,
respectively and similar infection rates were observed at 60 DAI (Table 5).
In order to understand the reaction of tungro viruses in Matatag 9 and IR64 of
older age, the rates of RTBV and RTSV infection were also examined in plants
inoculated at 21-days old. Mean RTBV infection rates of IR64 and Matatag 9 inoculated
at 21-days old were 90.7 and 24.3% at time of initial sampling and 96.4 and 32.9% at 60
DAI, respectively, Mean of RTSV infection rate in IR64 and Matatag 9 inoculated at 21-
days old were 69.9 and 2.1% at time of initial sampling and 90.7 and 5.0% at 60 DAI,
respectively (Table 6). No RTSV infections were detected in Matatag 9 at 7 DAI, 28
DAI, 35 DAI, and 42 DAI when the plants were inoculated at 21-days old (Table 6).
Relatively high RTSV infection rate was observed in IR64 at time of initial sampling as
well as at 60 DAI (Table 6). Infection rate of RTSV was extremely low in Matatag 9
regardless of the time of sampling when it was inoculated at 21-days old.
Temporal Change in the Accumulation of Tungro Viruses
Leaf samples of Matatag 9 and IR64 inoculated with both RTSV and RTBV at 6-
days old were collected weekly for 7 weeks. The optimum dilution rate for relative
quantification of RTBV accumulation was set at 50X based on a preliminary experiment
51

Table 5. Infection rate (%) of RTBV and RTSV at time of initial sampling and at 60 DAI:
6-day-old seedling
RTBV INFECTION a
RTSV INFECTION b
Initial Sampling 60 DAI Initial Sampling 60 DAI
Time of initial
sampling M 9 c
IR64 M 9 IR64 M 9 IR64 M 9 IR64
7DAI - - - - 10 55 5 65
14DAI 65 100 60 90 50 90 40 70
21DAI 45 90 45 85 25 80 25 80
28DAI 80 80 80 85 10 75 10 75
35DAI 75 95 75 90 25 55 25 40
42DAI 55 95 60 90 45 75 35 65
49DAI 60 90 60 100 20 60 20 65
MEAN 63.3 91.7 51.3 90 26.4 70 22.9 65.7
a = Infection caused by RTBV alone plus double infection caused by RTBV and RTSV
b = Infection caused by RTSV alone plus double infection caused by RTBV and RTSV
c = Matatag 9
52

Table 6. Infection rate (%) of RTBV and RTSV at time of initial sampling and at 60 DAI:
21-day-old seedling
RTBV INFECTION a
RTSV INFECTION b
Time of initial Initial Sampling 60 DAI Initial Sampling 60 DAI
sampling M 9 c
IR64 M 9 IR64 M 9 IR64 M 9 IR64
7DAI 5 70 20 100 0 40 0 95
14DAI 30 100 40 95 5 84.2 5 90
21DAI 10 85 20 95 5 75 5 95
28DAI 20 95 20 95 0 75 0 85
35DAI 35 95 40 95 0 75 5 95
42DAI 30 100 30 100 0 80 10 90
49DAI 40 90 60 95 5 60 10 85
MEAN 24.3 90.7 32.9 96.4 2.1 69.9 5 90.7
a = Infection caused by RTBV alone plus double infection caused by RTBV and RTSV
b = Infection caused by RTSV alone plus double infection caused by RTBV and RTSV
c = Matatag 9
53

using five 21 DAI samples of each test material. The levels of RTBV detected by ELISA
fluctuated in Matatag 9, while those in IR64 slightly increased from 14 DAI up to 42 DAI
and sharply increased at 49 DAI (Fig. 9). The relative titer of RTBV in Matatag 9 was
constantly higher than that in IR64.
Six-day old seedlings of test varieties were also inoculated with RTSV to evaluate
the temporal changes in RTSV accumulation. Optimum dilution rate was determined as
20X according to the results from a preliminary experiment. The level of RTSV in both
test materials was lowest at 7 DAI, however, in Matatag 9 it drastically increased and
peaked at 14 DAI and decreased at 28 DAI, then slightly increased at 35 DAI and slightly
decreased up to 49 DAI, while the levels of RTSV accumulation in IR64 drastically
increased up to 21 DAI, and sharply decreased (Fig. 9). The maximum level of RTSV
accumulation was higher in IR64 than in Matatag 9. It appeared that overall, the patterns
of temporal changes in the accumulation of RTSV in the two varieties were similar,
although the replication of RTSV may reach at the maximum level earlier in Matatag 9
than in IR64.
The temporal changes in virus accumulation were also examined in plants
inoculated at 21-days old. The optimum dilution rate for evaluation was determined as
30X. The level of RTBV accumulation in IR64 sharply increased at 14 DAI then rapidly
decreased at 21 DAI and slightly increased again at 28 DAI then decreased thereafter,
while that in Matatag 9 gradually increased up to 21 DAI, then decreased up to 35 DAI
and slightly increased thereafter. The accumulation levels of RTBV in both varieties
inoculated at 21-days old were considerably lower than those observed in plants
54

inoculated at 6-days old throughout the observation (Fig. 9). It seems that the
accumulation level of RTSV in IR64 inoculated at 21-days old was fluctuating
throughout the observation, peaking at 14 DAI. Meanwhile, it was shown that the
accumulation of RTSV in Matatag 9 inoculated at 21-day old was hardly detected after
peaking at 14 DAI.
Fig. 9. Temporal pattern of RTBV and RTSV accumulation in Matatag 9 and IR64. Both
6-day-old and 21-day-old seedlings were used at inoculation.
55

Although the levels of RTSV and RTBV accumulation did not show drastic difference
between Matatag 9 and IR64, far more severe symptoms were developed in IR64 than in
Matatag 9. Severe stunting and yellowing were observed in all infected IR64 whereas
Matatag 9 did not show typical RTD symptoms (Fig. 10).
Fig. 10. Symptoms casued by RTD on Matatag 9 (left) and IR64 (Right).
Matatag 9 did not show typical RTD symptom as compared with IR64
which showed yellowing and stunting symptom.
56

Settling Preference
Biological Characterization of Matatag 9
Resistance to Green Leafhopper
The number of viruliferous GLH that alighted on IR64 at 0.5 hr after infestation
was considerably lower than that at 8 hrs, and the number decreased slightly thereafter
(Fig. 11). In contrast, the number of GLH on Matatag 9 slightly increased from 0.5 hr to
4 hrs after infestation and then decreased. Chi-square test showed that no significant
value for deviation on insect count between IR64 and Matatag 9 at 0.5 hr after infestation
(x 2 = 1.52 NS , P = 0.22), however, it indicated highly significant preference of GLH for
IR64 over Matatag 9 at 4 hrs, 8 hrs, and 24 hrs after infestation (x 2 = 63.61 ** , x 2 =
172.75 ** , and x 2 = 177.21 ** , respectively. P < 0.01).
Comparison between the rates of virus infection in Matatag 9 and IR64
simultaneously infested with viruliferous GLH during the preference test indicated that
the infection rates with RTSV, RTBV and both RTSV and RTBV were higher in IR64
than in Matatag 9 (Table 7), although no significant correlation was found between the
number of insects alighting on test varieties and the rates of virus infections.
57

Fig. 11. Temporal changes in the number of viruliferous GLH on the seedlings of IR64
and Matatag 9.
Table 7. Average seedling infection (%) and average number of alighted insect per 5
seedlings of IR64 and Matatag 9 at different observation times from the GLH preference
test.
SEEDLING
NUMBER OF ALIGHTED INSECT/5
INFECTION
SEEDLINGS
Variety
RTSV
RTBV
RTBV RTSV 0.5 hr 4 hrs 8 hrs 24 hrs
IR 64 96 97 96
10.10 ±
1.59
22.95 ±
1.29
26.10 ±
0.86
23.85 ±
1.02
Matatag 9 11 49 19
8.90 ±
1.40
12.35 ±
1.53
8.75 ±
1.05
7.25 ±
1.05
58

Adult GLH Longevity
Range of the adult GLH longevity was from 2 to 41 days on IR64 whereas it was
from 2 to 19 days on Matatag 9. A significantly longer longevity of both male and female
adult GLH was observed on IR64 than that of Matatag 9 and resistant check variety IR62,
but there was no significant difference between Matatag 9 and IR62 (Table 8).
Meanwhile, the longevity of adult GLH on susceptible check variety TN1 significantly
differed from IR64. Significant difference in the longevity between sexes was found only
on TN1.
Nymphal Mortality
A significant difference on nymph mortality of GLH was observed among test
varieties at 3 days after infestation (Table 8). Nymph mortality on TN1 was lowest, and
significantly different from the others. A significantly less nymph mortality was
observed on IR64 than on both Matatag 9 and resistant check variety IR62, whereas no
significant difference between Matatag 9 and IR62 was found, suggesting that the two
varieties were equally resistant to GLH.
59

Table 8. Effect of antibiosis factor on GLH behavior and other life history traits
EFFCT OF TEST PLANTS ON GLH MEASURED ON THE
BASIS OF
TEST Adult Longevity Mortality Nymph Becoming Developmental Growth
VARIETY Male Female Mean (%) Adults, (%) Period, d Index
IR 62 4.9 ± 0.25a(a) 5.6 ± 0.38a(a) 5.18a 53.90 c 57b 19.32 ± 0.67b 2.98a
Matatag 9 5.3 ± 0.41a(a) 6.3 ± 0.67a(a) 5.78a 64.32 c 39c 19.39 ± 0.62c 2.05a
IR 64 11 ± 1.55b(a) 10.2 ± 1.38b(a) 10.6b 20.66 b 88a 15.35 ± 0.46a 5.78b
TN 1 25.9 ± 1.99c(b) 16.7 ± 1.36c(a) 21.3c 1.74 a 100a 13.94 ± 0.29a 7.2c
*Mean ± SE, Values followed by a common letter in a column are not significantly different at the 5% level by the LSD test.
*Values followed by same letter in parenthesis are not significantly different between sexes on each variety at the 5% level by the
LSD test.
*Growth index = percent nymphs becoming adults divided by mean developmental period.
60

Growth and Development of GLH Nymph
The nymph development period of Matatag 9 significantly differed from
susceptible check variety TN1 and IR64, but was not significantly different from resistant
check variety IR62 (Table 8). More than 80% of nymphs became adults on both IR64 and
TN1, while less then 40% of nymphs did on Matatag 9. A highly significant difference
was observed between Matatag 9 and IR64 or TN1, whereas there was no significant
difference between TN1 and IR64 in terms of the rate of nymphs becoming adult. In
growth index, the value for Matatag 9 was significantly lower than that of IR64 and TN1,
indicating that Matatag 9 is resistant to GLH nymph and may affect the transmission
behavior of GLH.
Matatag 9 with tungro resistance derived from O. rufipogon has been released as
stop-gap variety in the Philippines in 2002 (Khush et al. 2004). The resistance was
evaluated based on the Standard Evaluation System (INGER, 1996) in multilocation trials
(Cabunagan et al. 1999). There was, however, no intensive study on the resistance
mechanism of Matatag 9.
Forced test tube inoculation provides a more reliable measure of the resistance
status of test varieties as insects have no choice but to feed on the single seedling placed
in each tube (Azzam, 2000).
In this study, the rate of RTBV infection in Matatag 9 was relatively low when it
was inoculated with 1 GLH/plant. However, as the number of GLH increased, the
61

infection rate increased (Fig. 8.). The infection rates of RTBV in IR64 and in susceptible
check variety TN1 were consistently high regardless of GLH number. Therefore, these
results suggest that the level of RTBV resistance in Matatag 9 is weak or it may possess
resistance against other disease components which may interact with RTBV during the
disease development. Generally, the infection rates with RTBV and RTSV were low in
Matatag 9 except when more than 50% of Matatag 9 inoculated at 6-days old were found
infected with RTBV. The temporal changes in both RTBV and RTSV accumulation in
Matatag 9 appeared to be nearly similar to those of IR64 inoculated at either plant ages.
Relative level of RTBV accumulation was higher in Matatag 9 than in IR64 when the
seedling was 6-day-old at inoculation. Meanwhile, the relative level of both RTBV and
RTSV accumulation in the seedlings inoculated at 21-days old was lower than those
inoculated at 6-days old. These results indicate that Matatag 9 can be infected with both
RTBV and RTSV and that RTBV can infect in relatively high efficiency. It was also
shown that the level of RTBV accumulation was higher in Matatag 9 than in IR64 if
young seedlings become infected. Such lower levels of virus infection in older plants
could be accounted for by adult plant resistance involving indigenous plant defense
response to the insect and plant pathogen. Ling and Palomar (1966) and Gibbs and
Harrison (1976) demonstrated that plants may become more resistant to virus infection as
they grow older, while young plants are more vulnerable to virus infection. As plants
grow, physiological structures such as thickness of epidermal layer and leaf surface
condition generally change and such changes may affect the insect feeding behavior.
Thus, even though insects settle on plants for a long time, some insects may not acquire
62

inoculum sufficient for effective virus transmission. Harris and Harris (2001) described
that aphids eventually face the problem of p-protein fibrils and callose clogging which
may prevent the entrance of plant sap into the maxillary food canal though aphids are
given sufficient feeding time. In addition, feeding in a virus-infected plant may coat the
cuticular lining of the feeding apparatus with ACR-HC-virion complex.
The results in this study showed that once RTBV and RTSV are introduced into
Matatag 9, both viruses are likely to replicate in Matatag 9 using their typical replication
pathway though symptom development was deterred in Matatag 9, indicating that
Matatag 9 has tolerance against RTBV. On the other hand, Matatag 9 could be considered
as resistant to RTSV based on the infection rate in aged plants, though the accumulation
of RTSV in Matatag 9 is still readily detectable.
Matatag 9 was found to be a less preferred host than IR64 by GLH for settling,
implying the contribution of antixenosis characteristics to resistance of Matatag 9. The
mean GLH count on seedling of Matatag 9 did not significantly differ from that of IR64
at 0.5 hr after infestation, showing that insects moved to the seedling without recognizing
their preferred host. GLH, thereafter, migrated from Matatag 9 to IR64, the number of
settled GLH on IR64 significantly increased at 4, 8, and 24 hrs after infestation, probably
because they recognized features adverse to their feeding in the host. Moreover, during
the experiment, it was observed that the insects that settled on Matatag 9 became restless,
indicating some interference with their feeding on Matatag 9. Similar observation was
reported by Karim (1978). For many phytophagous insects, visual and chemical cues play
an important role in host selection (Dixon, 1985). Insects often examine the plant surface
63

cues by repeatedly tapping the tip of the labium against the plant surface and determine if
the plant is suitable for settling or feeding (Bakus, 1985). As the insect identify
appropriate probing site, they insert their stylet into the plant surface then suck the plant
sap whether the potential host contains appropriate nutrition or not (Kawabe and Mclean,
1980). Therefore, it takes a certain time for the insects to recognize their preferred host.
Short adult longevity, more than 60% nymph mortality, long nymph
developmental period and low percentage of nymph becoming adult are indicative of
antibiosis effects of Matatag 9 (Kishino and Ando, 1978; Liu and Takahashi, 1990).
Moreover, growth index on Matatag 9 was significantly lower than both IR64 and TN1,
while IR62 had almost same growth index value (Saxena et al. 1974), supporting
significant involvement of antibiosis effect in resistance against RTD in Matatag 9.
Collectively, the results of this study strongly suggest that the resistance of
Matatag 9 is mainly due to insect resistance although the contribution of resistance
against tungro viruses in Matatag 9 cannot be ignored.
Virus infection and symptom development are the consequence of virus-vector-
host complex interaction. Since RTD is a composite disease caused by RTBV, RTSV and
insect vectors, the infection mechanism and symptom development might be more
complex than those by other viruses. Knowing the resistance mechanism not only in
Matatag 9 but also in other rice varieties enables us to formulate more appropriate
combination for the mixed seeds planting. Also, it would definitely contribute to the
design of deployment strategies for resistant varieties.
64

Performance Evaluation of Varietal Mixture Components
Comparative Morphological and Yield Characteristics
of Matatag 9 and IR64
Both Matatag 9 and IR64 similarly grew until harvest without any distinct visual
differences (Fig. 12). Fifty percent flowering was recorded at 66 and 77 DAT for IR64
and Matatag 9, respectively. Both varieties were ready for harvesting by 107 DAT (Fig.
12). Significant difference in height between the two varieties during the growth period
was observed at 45, 75, and 90 DAT (Fig. 13), however, the difference was less than
approximately 5 cm. The numbers of tillers at 30 and 60 DAT did not show significant
difference between varieties (Table 9). Significant differences were observed in final
height and panicle length between varieties while no significant differences were
observed in the number of productive tiller and the numbers of filled/unfilled grain per
panicle at harvest time (Table 10). There were significant differences in grain size (width
and length) and TGW between varieties (Table 11).
65

Matatag 9 IR 64
Fig. 12. Morphological appearance of Matatag 9 (left) and IR64 (right) at 107 DAT in the
screenhouse
a
a
a
a
a
b
0.0 15 30 45 60 75 90
Day after transplanting (DAT)
a
a
a a
b b
*Treatment means at different DAT followed by a common letter are not significantly
different at the 5% level by the LSD test.
Fig. 13. Growth comparison between Matatag 9 and IR64 at every 15 days interval.
66

Table 9. Comparison of tiller number during vegetative stage
TEST VARIETY 30 DAT 60 DAT
Matatag 9 8.06 ± 0.44a 17 ± 0.63a
IR 64 7.56 ± 0.54a 17.13 ± 0.84a
*Mean ± SE, Values followed by a common letter in a column are
not significantly different at the 5% level by the LSD test.
Table 10. Comparison of agronomic traits of mixture components at harvest
TEST NUMBER OF GRAIN/PANICLE
VARIETY Final Height Panicle Length Productive Tiller Filled Unfilled
Matatag 9 96.74 ± 0.76a 23.39 ± 0.27a 14.19 ± 0.58a 129.83 ± 3.95a 10.88 ± 0.85a
IR 64 91.35 ± 0.90b 24.5 ± 0.33b 14.63 ± 0.94a 116.65 ± 4.88a 17.31 ± 2.43a
*Means followed by a common letter in a column are not significantly different at the 5% level
by the LSD test.
Table 11. Comparison of physical characteristics of grain
TEST HULLED DEHULLED 1000 GW [g]
VARIETY Width Length Width Length Hulled Dehulled
Matatag 9 2.12 ± 0.01b 9.87 ± 0.05a 1.89 ± 0.01b 7.41 ± 0.04a 23.4 ± 0.24b 18.2 ± 0.24b
IR 64 2.33 ± 0.01a 9.48 ± 0.05b 2.09 ± 0.01a 6.98 ± 0.03b 26 ± 0.00a 20.6 ± 0.24a
*Means followed by a common letter in a column are not significantly different at the 5% level
by the LSD test.
67

Effect of Mixed Planting of Resistant and
Susceptible Varieties on the Incidence of Rice Tungro Disease
To evaluate the effect of mixed planting patterns, namely mixed seed planting and
interplanting, the relative rates of infection with RTSV, RTBV, and both RTBV and
RTSV in each planting pattern were compared.
Reduction in disease was observed with the increase in the proportion of resistant
component among treatments on the mixed seed planting and interplanting regardless of
the viruliferous GLH level except relative total RTBV infection (RTB) at 10 GLH level
(Fig. 14). Disease reduction was more evident in mixed seed planting than in
interplanting at both GLH levels. At 3 GLH level, the effect of mixed seed planting on
RTB and relative total RTSV infection (RTS) seems to be more significant than that of
interplanting, while no significant difference on relative rates of infection with both
RTBV and RTSV (RBS) was observed between planting types. At 10 GLH level, no
significant differences between planting types were observed among RBS, RTB and RTS.
The results of mean comparison among treatments between planting types showed
that the effect of mixed seed planting on both RTB and RTS was significantly different
from interplanting in both 75% R: 25% S and 25% R: 75% S at 3 GLH level.
Interestingly, the RTB and RTS in the interplanting of 75% R: 25% S were not
significantly different from those in the mixed seed planting of 50% R: 50% S.
68

Infection rate (%) RBS
RTB
Infection rate (%)
RTS
Infection rate (%)
a
a
a
a
a a
b
b
b
3 GLH
c
c
d
c cd
c
b
d
cd
d
e
f
d
d
e
a
a
a
ab
a a
b
ab
ab ab
bc
a b
10 GLH
b
b
c
b ab b
Fig. 14. Relative rates of infection with RTBV+RTSV (RBS), total RTBV (RTB), and
total RTSV (RTS) observed in mixed seed plantings and interplantings. The relative rates
were computed based on those observed in the pure stand of IR64 (100% S).
* Bar having a common letter are not significantly different at the 5% level by the LSD
test.
c
bc
d
c
b
d
69

Moreover, RTB in the interplanting of 50% R: 50% S was not significantly different from
that in the mixed seed planting of 25% R: 75% S at 3 GLH level. At 10 GLH level,
however, no clear statistical differences between planting types were observed in any
treatments, although there were significant differences among treatments for the RBS and
RTS but not for RTB.
Serial-Inoculation in Resistant and Susceptible Varieties
GLH was able to transmit both RTSV and RTBV to 1 st plant regardless of variety
but infection rates of viruses in Matatag 9 were significantly lower than in IR64 (Fig. 15).
When the 2nd plant is Matatag 9, GLH failed to transmit either RTSV or RTBV (C1 and
2). On the other hand, when the 2nd plant is IR64, GLH was able to transmit either
RTSV or RTBV (C3 and 4). A few GLH successfully transmitted RTBV up to 4th plant
(C4).
70

% Infection
100
90
80
70
60
50
40
30
20
10
0
M9
M9
M9
C1 C3
% Infection
100
90
80
70
60
50
40
30
20
10
0
IR64
M9
IR64
M9
M9
M9
IR64
C2 C4
BS
B
S
BS
BS
B
S
BS
S
B
S
B
Fig. 15. Duration of virus retention ability through 5 days serial-inoculation with different
combinations of resistant and susceptible varieties. C1 and C4 represent monoculture. C2
and C3 represent varietal mixtures. C1 and C3: 1 st plant is resistant variety Matatag 9. C2
and C4: 1 st plant is susceptible variety IR64. C1 and C2: 2 nd plant Matatag 9. C3 and C4:
2 nd plant IR64.
% Infection
% Infection
100
90
80
70
60
50
40
30
20
10
100
90
0
80
70
60
50
40
30
20
10
0
M9
IR64
IR64
IR64
M9
IR64
IR64
IR64
M9
IR64
BS
B
S
BS
BS
B
S
BS
S
B
S
B
71

Development of varieties with good agronomical characteristics as well as
appropriate disease and pest resistance became one of the requirements for
biodiversification since the commercial use of variety mixture is increasing and some
degree of agronomic trait uniformity is desired (Mundt, 2002; Smithson and Lenne, 1996;
Garret and Mundt, 1999). Mixture components are usually mixed in a replacement
design (Zhu et al. 2005) to avoid a contamination with other mixture components and to
maintain market value.
Growth comparison and evaluation of yield components between Matatag 9 and
IR64 showed that they have similar agronomical characteristics. Although statistical
analysis showed significant differences in few characteristics, the actual differences
between them were virtually negligible and may not influence farmers’ harvest practices.
Thus, Matatag 9 and IR64 can be mixed and harvested together. Significant difference in
TGW was observed between Matatag 9 and IR64. The yields from the mixtures, however,
planted in RTD endemic area were not significantly different from the highest yields
achieved by the monocultures of either Matatag 9 or IR64 (Cabunagan and Choi. 2005).
Yield difference between monocultures from the field trial was approximately 10%
which was comparable to the result of the present study. Smithson and Lenne (1996)
pointed out that yield in mixture plots usually lie above the mean of their components in
monoculture. Yield increases of 1 to 5% are often provided by a variety mixture in the
absence of substantial disease, with larger increases when disease is of significance
(Mundt, 2002). In the Philippines, the interplanting approach to manage RTD was
initially attempted, however, a majority of farmers were not willing to adopt the laborious
72

practice. Instead, the mixed seed planting was designed, aiming for wider adaptation of
the variety mixture as one of the RTD management strategies among farmers (Cabunagan
and Choi, 2005).
The results of tray inoculation suggest that the mixed seed planting seems to be
more effective to reduce RTD incidence than interplanting in an area when the disease
pressure is not extremely high. Since there is no significant difference between the two
planting methods at 10 viruliferous GLH, both methods would be less effective likewise
in an area where disease pressure is high. Possible explanation of the difference in
effectiveness on disease reduction between the two methods is the difference in spatial
distribution of mixture components. As both Matatag 9 and IR64 in the mixed seeds
planting are randomly distributed, it generates an inconsistent spatial pattern that may
influence the movement and feeding behavior of insect vector. For example, when
viruliferous GLH from outside alight on Matatag 9, the insects may be forced to transfer
to other plants due to the antixenosis or antibiosis effects of Matatag 9, but the insects
alighted on IR64 would stay longer. Interplanting provides a consistent spatial
distribution of mixture components. It seems to be easier for insects to reach their
preferred host in the interplanting arrangement. The insect movement in interplanting
may require shorter distance than that in mixed seed planting since IR64 was planted in
consistent pattern and infection rate is higher than mixed seed planting. Thus, one of the
potential mechanisms for the reduction of RTD in the mixed seed planting is the random
spatial distribution of individual resistant plants.
73

RTBV and RTSV can be transmitted during host selection events such as sylet
probing on plant tissue and plant fluid ingestion regardless of varieties though RTD
infection rate is low in Matatag 9. Insects alighted on IR64 may settle longer, while those
landed on Matatag 9 may move to other plants, thus virus retention ability could be
decreased. RTBV and RTSV can be transmitted with low efficiency to the second IR64
but no virus transmission occurs in Matatag 9. Although GLH can retain RTBV for 4-5
days and RTSV for 2-4 days (Hibino et al. 1978), once the insects feed on Matatag 9,
they may lose their virus retention ability. Matatag 9 may contain certain factors which
inhibit the binding between viruses and leafhopper cuticula or suppress the activity of
helper component required for the binding between virus and cuticula at retention sites of
the leafhopper (Harris and Harris, 2001).
74

Farmers’ Perception Survey on the Use of Mixed Planting
Respondents’ profile. More than 80% of the farmers who attended the forum
were residents of Barangay Progreso, the site of the 4 season field trial on “Mixed seed
planting” in the field of Mr. Domingo Bonifacio. The other respondents came from
neighboring barangays. Their age ranged from 27 years to 74 years old with an average
of 50.5 years old. Around 90% or more of the farmers were married and more than half
has a family size of 6. The average period of formal education for all farmers in the
sample was 8.3 years and about 42% were at least Elementary School educated, and 48%
were High School educated. About 44% were tenant and another 38% either share holder
or 10% share farmer. The average rice farming experience is about 18 years (Table 12).
Farm profile. The area being utilized as rice field ranged from 0.25 ha to 12 ha
with an average of 2.48 ha (Table 12). As shown in Table 13, majority of the farmers
were planting improved varieties such as PSB Rc 14, 10, 82 and 28. Except for PSB Rc
10, all the rest are known to have good eating quality and thus highly favored by farmers
in the area. Furthermore, most PSB Rc varieties are carrying Xa4 gene for resistance to
bacterial leaf blight, except for PSB Rc 82 which carries Xa4+xa5. NSIC Rc 110 is
newly released tugro resistant variety in 2002. Some farmers planted IR64 from time to
time because of its superior agronomical performance. Although these varieties could be
75

Table 12. Profile of farmer respondents of the survey in Ajuy, Iloilo, Philippines
Age (years) Mean 50.45
Min 27
Max 74
PERCENTAGE OF
52 RESPONDENTS
Civil status Married 47 90.4
Single 3 5.8
Widow 1 1.9
Not specified 1 1.9
Family size Mean 5.8
Min 2
Max 14
Education Mean 8.25 EG 30.8
(years) Min 2 HSG 44.2
Max 14 CG 9.6
ED 11.5
HSD 3.9
Land ownership Owner 15.4
Tenant 44.2
Share holder 19.2
10% share farmer 19.2
Rice field (ha) Mean 0.25
Min 2.48
Max 12
Farming
experience Mean 18.27
(years) Min 2
Max 50
EG = Elementary Graduate, HSG = High School Graduate, CG = College Graduate,
ED = Elementary Dropout, and HSD = High School Dropout.
76

Table 13. Varieties planted for the past 4 seasons among 52 respondents in Ajuy, Iloilo,
Philippines
VARIETY PERCENTAGE OF 52 RESPONDENTS
PSB Rc 14 96.2
PSB Rc 10 65.4
PSB Rc 82 34.6
PSB Rc 28 34.6
IR64 25
PILIT (Gultinous) 17.3
NSIC Rc 110 15.4
PSB Rc 112 13.5
PSB Rc 18 9.6
Mixture 3.8
PSB Rc 64 3.8
PSB Rc 80 3.8
PSB Rc 4 3.8
Matatag 6 1.9
PSB Rc 44 1.9
PSB Rc 12 1.9
PSB Rc 17 1.9
PSBRc 72 1.9
Red Rice 1.9
77

acquired either from seed grower or institutional sector, most farmers (69.2%) obtained
them from other farmers. In addition to the seed purchase, one of the mixture components,
Matatag 9, is available in Ajuy (Ely Sandig, Chief, RAID, personal communication).
Around 15% of the farmers were doing rice production for home consumption, whereas,
the others produced for either only commercial or both.
All farmers reported various pests and diseases as their common problems in their
rice farm. RTD was regarded by farmers as the most important disease in the area
followed by bacterial leaf blight and rice blast. More than half of farmers regarded stem
borer, rice bug, and GLH/BPH, “waya waya” in Ilongo, as their major pest problems.
Aside from these, non-insect pests such as rat, giant apple snail, and maggot were also
reported by a few farmers (Table 14).
78

Table 14. Percentage of farmers reporting major pests and diseases on rice farming in
Ajuy, Iloilo, Philippines
PLANT DISEASE AND PEST PROBLEM a
PERCENTAGE OF 52
RESPONDENTS
Plant diseases
Rice Tungro Disease (RTD) 65.4
Bacterial leaf blight 26.9
Rice blast 17.3
Bacterial leaf streak 7.7
Sheath blight 3.8
None 15.4
Insect pest
Stem borer 55.8
Rice bug 51.9
Green Leafhopper (GLH) 48.1
Brown hopper (BPH) 23.1
GLH/BPH (waya waya) b
32.7
Armyworm 19.2
Leaf holder 19.2
Caseworm 7.7
Cutwarm 1.9
Non-insect pest
Rat 5.8
Giant apple snail 5.8
Maggot 1.9
Others c
a
Multiple answers possible
23.1
b
General insect name was used in local language
c
Unidentified insect reported by farmers
79

Farmers’ Awareness and Knowledge of Rice Tungro Disease
Most farmers (86.5%) were aware of RTD and more than 70% had experienced
damage by the disease at least either once or twice for the past 5 years. However, the
damage was ranked either least serious or moderately serious (Table 15).
There was a wide range of responses among farmers about the causes and mode
of RTD spread what causes RTD and how it is spread from plant to plant. Although,
majority of farmers recognized virus as the main causal agent of RTD, more than half of
them mention other factors that were not causal agent such as poor soil, water and seeds
(Table 16). Fewer farmers (5.8%), in fact, correctly answered both virus and GLH. Some
other farmers (46.2%) purely believed that RTD was not caused by virus.
Table 15. Farmers’ experience of RTD incidence in their farm and its damage
seriousness ranked by farmers
PERCENTAGE OF 52 RESPONDENTS
Number of RTD incidence
Once 36.5
Twice 28.8
Three times 5.8
Four times 1.9
Five times 5.8
Ten times 5.8
None 15.4
Severity of RTD incidence
Most serious 13.5
Moderately 38.4
Least serious 34.6
Not serious 11.5
No answer 1.9
80

Table 16. Farmers’ perceptions of causes and spread of RTD a
PERCENTAGE OF 52 RESPONDENTS
Causes
Virus 51.9 (9.6)
Insect (general) 36.5
Poor seeds 36.5
Bacteria 26.9
Fungi 23.1
Poor soil 19.2
Poor water 11.5
Spread
GLH 57.7 (7.7)
BPH 28.8
Water 19.2
Seeds 19.2
Wind 5.8
Others 1.9
a Multiple answers possible
* Value in parenthesis representing the percent farmer answered properly.
Less than half of farmers (40.4%) believe that water, seeds or BPH spread RTD and more
than 50% consider GLH to spread the disease.
Farmers could differentiate a RTD infected plant from other diseased plants based
on either the change in leaf color, stunting of the plant or the presence of plenty of GLH
in their field.
Farmers’ Awareness of Rice Tungro Disease Control
Although almost equal percentage of farmers controlled RTD in their rice field by
either using insecticides or using resistant varieties, majority believed that the use of
81

insecticides could not control RTD or it was not effective (Table 17). About 29% of the
farmers answered that they removed tungro infected plant from their field. A few farmers
used RTD control methods such as drying a rice field after harvest, and application of
zinc sulfate, or filling paddy field the water and then draining it. Additionally, the farmers
were asked to name the insecticide they used or the resistant variety they planted in their
field. NSIC Rc 110, IR60, and Mixtures appeared where varieties were planted.
More than 60% of the farmers were aware that resistant varieties are available for
the control of RTD and more than 70% had experienced breakdown of resistance to RTD
of the varieties they planted (Table 18).
Table 17. Farmers’ control measures for rice tungro disease and perception of insecticide
effectiveness
PERCENTAGE OF 52 RESPONDENTS
Control measures a
Spraying insecticide 55.8
Using resistant variety 51.9
Removal of infected plant 28.8
Others 11.5
Perception of insecticide effectiveness
Effective 19.2
Not effective 76.9
No answer 3.8
a Multiple answers possible
82

Table 18. Farmers’ awareness of the availability of tungro resistant variety and
experience of resistance breakdown.
PERCENTAGE OF 52 RESPONDENTS
Availabity of resistant variety
Yes 65.4
No 32.7
No answer 1.9
Experience of resistance breakdown
Yes 71.2
No 28.8
No answer 0
Awareness of Mixed Seeds Planting
Although 60% of the farmers were aware of the availability of resistant rice
varieties, only 46% of the respondents were aware of the mixed seed planting (Fig. 16 A),
and 79% of those who were aware believed that it was effective for controlling RTD and
only 17% believed otherwise (Fig. 16 B). About 70% of those who were aware had tried
mixed seed planting either for 1 or 2 seasons (Fig. 16 C), and more than 70% had
observed the effectiveness of mixed seed planting for controlling RTD. However, only
about 50% of those who were aware and had tried mixed seed planting would
recommend the practice to other farmers.
83

Percent of respondent
A
No (28)
Yes (24)
B
Fig. 16. Farmers’ awareness of the mixed seeds planting for rice tungro disease control
(A), their belief of control effectiveness (B), and experience of the mixed seeds planting
in their field (C).
At present, about 70% of the farmers who tried mixed seed planting stopped
applying this method and the reason they gave were: that they did not have RTD
incidence in their farm (35.3%) or they consumed all the seeds and none was available
for next season planting (29.4%). Twenty-four percent farmers stopped planting because
they believed that mixed seed planting had no effect in controlling RTD (Table 19).
84
C

The reason why 54% of the respondents were not aware of the mixed seed
planting was either because they really have no knowledge about it (43%) or they have
no access to seeds of mixtures (36%) that they could use. However, after hearing the
presentation about mixed seed planting during the forum, more than 80% were willing to
try it in the future.
Table 19. Major reasons for the termination of the mixed seed planting and its adaptation
constraints in farmers’ field in Ajuy.
REASON / CONSTRAINT a
NUMBER OF
RESPONDENTS
Reason of termination n=17 b
No rice tungro 6
Consumed seed 5
No effect 4
No answer 2
Laborious 0
Constraint of adaptation a
No knowledge about the mixed seed planting 16
No access to mixed seed 10
Doutful 3
Have not tested yet 2
Do not like
a
Multiple answers possible
b
Farmers who had tried the mixed seed planting
1
c
Farmers who had never tried the mixed seed planting
n=28 c
85

Farmer survey is an important data gathering process for assessing the needs of
intended beneficiaries to determine their knowledge and perceptions of a pest problem,
their constraints in dealing with the problem, and their attitudes and practices in pest
management (Escalada and Heong, 1997).
The present survey showed that farmers viewed pests and diseases, especially
RTD and the stem borer, GLH, and rice bug, as primary constraints to rice production in
Ajuy, Iloilo (Table 14). Most farmers were able to distinguish the major rice pests and
diseases and their awareness of RTD was considerably high. Relatively high knowledge
of RTD and its management was observed in this study. The reason is probably that most
farmers had participated in the farmers training on RTD management as part of the IRRI-
ILOILO PAO DAPITSAKA 2000-2002 Project in Ajuy, Iloilo. In general, farmers’ in-
depth knowledge about pests is associated with the visibility and importance of the pest,
since disease pathogens are not easily seen, it is difficult for farmers to account for the
causes of diseases (Bentley and Thiele, 1999). In fact, although majority of farmers
regarded the virus as causal agent and GLH as the agent of spread, they believed that the
disease incidences were caused by not only the interaction between virus and GLH but
also the interaction among the virus and other microorganisms or poor soil, water and
seeds condition (Table 16). There seemed to be confusion with the mechanism of RTD
incidence among the farmers. Though fewer knew the causal agent and its vector, the
information would not likely be disseminated properly from the farmers who have correct
knowledge to the other farmers. The reason might be that the farmers who knew the
mechanism of RTD incidence had difficulties in explaining the details appropriately to
86

other farmers. This phenomenon could be explained by studies concerning beliefs about
the causes of human disease in the Philippines. The study revealed that people often have
complex views of the cause and effect of disease, with several causes often associated
with one or more effects rather than one cause leading to one effect. Often a combination
of a person’s susceptibility, perhaps caused by hunger or fatigue, plus an expected natural
phenomenon such as a sudden heavy rain is thought to result in sickness (Himes, 1971).
Consequently, they associate RTD to human diseases like AIDS or cancer (Warburton et
al. 1997), therefore, their belief that RTD could be spread by air, water and soil is
consistent with their perception that it is comparable to human pathogens.
In the case of RTD management options, farmers usually rely on spraying
insecticide and on using resistant variety in their farm although they are aware that the
resistance may break down over time and using insecticide was not effective in
controlling RTD (Tables 17 and 18). Some farmers remove (rogue) infected plants from
their field and fewer apply other cultural managements such as drying a rice field.
Farmers generally find rouging is time-consuming and tedious and additional labors may
be required. In addition to the insecticide and resistant variety, the study revealed that
some of farmers have used a banned insecticide and/or an inappropriate resistant variety.
The reason would be the limited information resources among farmers. A Department of
Agriculture (DA) technician is the main source of information on tungro. The
technician’s recommendations of RTD control for farmers included using either spray or
granular insecticide, rouging, plowing a whole field, and draining a field, but those were
varied from area to area. Learning from other farmers and from their own experience
87

were also important (Warburton et al. 1997). In Ajuy, most farmers obtained their seeds
from neighboring farmers while others acquired them from their seed growers or the
institutional sector. There seems to be a lack of accessibility of information (network
system) in the area.
Over the years, farmers have developed methods of managing plant diseases.
However, changes and intensification within farming system often bring increased
disease pressures. RTD affect large areas and poses difficulties for farmers because of its
unpredictability and risk of major crop loss. Local knowledge and practices of farmers
must evolve to cope with these problems. Efficient communication technology and
technology transfer scheme have to be applied among scientists, extension technicians,
and beneficiaries. Farmers’ perception surveys on pest management and practices in
Southeast Asia have revealed that most farmers are risk adverse (Rola and Pingali, 1993;
Heong et al. 1994). Farmers in the Philippines regarded RTD as a serious problem even
in areas where outbreaks are rare. Also, they ranked RTD highly among diseases despite
the relatively low frequency of outbreaks because it was extremely destructive when it
occurred and enormously difficult to control (Warburton et al, 1997). People tend to
perceive risks with unknown and uncontrollable aspects as greater than those with known
and more controllable characteristics even though the probability of the event is much
less (Slovic, 1987).
Farmers’ perception of diseases and their understanding of pathogen ecology are
important factors that influence on their adoptability of newly developed control methods
(Nelson, 2001). Knowing the farmers’ perception of the mixed seeds planting is
88

necessary for further development of technology transfer scheme to implement this new
technology effectively to farmers.
The present study showed less than half of respondents had expressed the awareness of
the new technology “mixed seed planting” (Fig. 16 A). The mixed seed planting had
never been introduced to the farmers and this could be the reason of much unawareness
of this new RTD management option among other respondents. Although there were four
seasons field trial of “mixed seed planting” conducted in the field of Mr. Domingo
Bonifacio, no farmer field day was ever conducted for other farmers to observe the trial.
Only fewer inquisitive farmers had a chance to observe the trials. There were several
farmers' constraints related to the adaptation of the mixed seeds planting such as no
knowledge of this new technology, no access to the mixed seeds, or doubts about the new
technology itself. These constraints have to be considered as farmers' inputs associated
with the adaptability of mixed seeds planting.
In contrast, among the farmers who were aware of the mixed seed planting, belief
of control effectiveness was considerably high and trials had been performed in their rice
field (Fig. 16 B and C), implying a high possibility of this new technology adaptation
among farmers though half of them, at present, would not recommend this new scheme to
other farmers. Moreover, none of them considered this new RTD management scheme as
tedious and laborious technology, a fact that should increase the possibility of the
farmer's adaptation of this control method. In addition, after the new technology was
discussed to the farmers during the forum, more than 80% of the farmers were willing to
try the mixed seed planting in the future although farmers are satisfied with their current
89

ice quality. In addition to the grain quality, all respondents expressed their desire for
high eating quality. Farmers want to plant varieties with much IR64-like quality traits.
Farmer involvement in research and extension have been practiced in many places
(Nelson, 2001). Involving farmers in the research process increases the chance of success
in generating an effective agricultural technology (Rhoades and Booth. 1982).
Participatory approaches offer researchers a mechanism to ensure that their work is
relevant to farmers’ needs and conditions (Pretty, 1995; Selener, 1997). Thus, in order
for farmers to understand the features of mixed seed planting, farmer participatory
research approach will be adequate to diffuse this new technology effectively to farmers.
90

Grain Quality Evaluation of Mixed Seed Planting
Milling quality. Rough rice samples from the different treatments had similar
percentage of brown rice and milled rice with brown rice ranging from 72-74% and
milled rice from 61-64% (Fig. 17). The highest percentage of head rice recovery was
from rough rice harvested in 25% R: 75% S (43.6%) and followed by 100% S (pure stand
IR64), whereas, the lowest percentage was found in 75% R: 25% S.
Analysis of the milled rice revealed that percentage of whole grain in mixtures
were comparable with 100% S or 100% R (pure stand Matatag 9) except for that in 75%
R: 25% S and broken rice were also highest in 75% R: 25% S (31%), while, other
mixture treatments had a comparable percentage of broken rice to 100% S (Fig. 18).
Fig. 17. Milling yield of the rough rice harvested from plots planted to different
seed mixture ratio of R (resistant Matatag 9) and S (susceptible IR64).
91

Fig. 18. Percentage of whole grain and broken rice from rough rice harvested
from plots planted to different seed mixture ratio of R (resistant Matatag 9) and
S (susceptible IR64) analyzed by Cervitec 1625 Grain Inspector
Grain size, shape and appearance. Grain appearance largely determines market
acceptability of milled rice and grains from mixtures with very low chalkiness could be
readily accepted by consumers in the Philippines.
Visually all the samples from the different treatments had similar appearance in
terms of shape and size (Fig. 19) and these were confirmed by the average length and
width of the milled grains as measured by Cervitec 1625 Grain Inspector (Table 20). The
grains from mixture treatments were classified into long and slender rice grain based on
the size (Table 3-a) and shape (Table 3-b) classification and its ratio in this study. This
grain type is preferred by millers in the Philippines.
92

Fig. 19. Grain appearance of rough rice (paddy) and milled rice from each treatment.
93

Table 20. Grain length and width of milled rice harvested from plots planted to different
seed mixture ratio of R (resistant Matatag 9) and S (susceptible IR64) analyzed by
Cervitec 1625 Grain Inspector
TREATMENTS NUMBER OF
GRAINS
ANALYZED
AVERAGE
LENGTH
(mm)
AVERAGE
WIDTH
(mm)
94
LENGTH/WIDTH
RATIO
100% R 519 6.8 ± 0.3 1.9 ± 0.2 3.6 ± 0.5
75% R : 25% S 348 6.7 ± 0.3 1.9 ± 0.3 3.5 ± 0.7
50% R : 50% S 537 6.7 ± 0.3 1.9 ± 0.2 3.5 ± 0.5
25% R : 75% S 460 6.7 ± 0.3 2.0 ± 0.2 3.4 ± 0.5
100% S 483 6.7 ± 0.3 2.0 ± 0.2 3.4 ± 0.5
Milled grains of pure stand Matatag 9 were more translucent than those of pure
stand IR64 as shown by the high percentage (74.5%) of grains having only less than 10%
chalkiness as compared to 55.5% in pure stand IR64 (Table 21). Milled grains from
mixture treatments had better (high percentage with less than 10% chalkiness) grain
appearance than pure stand IR64.
Table 21. Degree of chalkiness of milled rice harvested from plots planted to different
seed mixture ratio of R (resistant Matatag 9) and S (susceptible IR64) analyzed by
Cervitec 1625 Grain Inspector
NUMBER OF CHALK CHALK CHALK CHALK CHALK
TREATMENT GRAINS ANALYZED 0-10 % 10-25 % 25-50 % 50-75 % > 75 %
100% R 519 74.5 23.9 0.7 0.9 0
75% R : 25% S 348 58 39.7 0.9 0.5 0.9
50% R : 50% S 537 70.6 28.5 0.2 0.5 0.2
25% R : 75% S 460 61.6 36.6 0.6 1 0.2
100% S 483 55.5 42.9 0 0.9 0.7

Amylose content and gelatinization temperature. Pure IR64 had higher amylose
content than pure Matatag 9 (Table 22), however, all treatments had amylose content
within the range of 20-25% that belongs to the intermediate type which is preferred by
consumers in the Philippines.
The gelatinization temperature of starch determines the time required for cooking.
Gelatinization temperature is the temperature at which 90 - 98% of the starch granules
swell irreversibly in hot water with loss of crystallinity and birefringence.
Generally, gelatinization temperature ranged from 55° to 79°C. The gelatinization
temperature of rice varieties could be estimated based on the spreading score and
classified as low (55° to 69 °C), intermediate (70° to 74°C), or high (>74°C). As shown
in Table 22, milled grains from the different treatments had gelatinization temperature of
intermediate to high intermediate.
Table 22. Amylose content and gelatinization temperature of milled rice harvested from
plots planted to different mixture ratio of R (resistant Matatag 9) and S (susceptible IR64)
TREATMENT AMYLOSE CONTENT,% GT*
100% R 20.5 HI
75% R : 25% S 20.6 HI
50% R : 50% S 19.7 2HI/I
25% R : 75% S 21.4 2HI/I
100% S 22.2 1HI/I
*HI = high intermediate; I = Intermediate; 1, 2 = number of grain in different category from the rest among
6 grains
95

Gel consistency From the viscosity measurements as shown in table 23, it showed
that pure stand Matatag 9 cooked rice was harder (low breakdown and high set back) than
pure stand IR64. The viscosity curve of mixed rices showed similarity to that of pure
stand IR64 (Fig. 19). The hardiness of the cooked rice (consistency) of all treatments was
very similar although Matatag 9 was a little harder and IR64 was soft. The texture of the
mixture treatments was soft compared to Matatag 9 but harder than IR64. The appearance
and texture of the cooked mixed rice (T2-T4) was very similar to IR64.
Table 23. Viscosity analysis of cooked milled rice harvested from plots planted to
different mixture ratio of R (resistant Matatag 9) and S (susceptible IR64) by the Rapid
Visco Analyzer.
TROUGH TREATMENTS
100% R 75% R : 25% S 50% R : 50% S 25% R : 75% S 100% S
Peak Viscosity (PV) 2386 2795 2691 2881 2919
Trough 1421 1504 1478 1562 1542
Final Viscosity (FV) 3007 3076 3022 3127 3087
Breakdown 1
965 1291 1213 1319 1377
Setback 2 621 281 331 246 168
Consistency 3
1586 1572 1544 1565 1545
1 2 3
= peak viscosity - trough, = final viscosity - peak viscosity, = final viscosity – trough
Sensory evaluation of the cooked rice. The appearance and texture of the cooked
rice from the T2-T4 treatments was very similar to IR64. Matatag 9 cooked rice texture
was a bit hard while IR64 was obviously soft. The mixture treatments showed softer
cooked rice than Matatag 9 but were not as soft as IR64.
96

PV
Trough
Fig 19. Viscosity curves of cooked milled rice harvested from plots planted to
different mixture ratio of R (resistant Matatag 9) and S (susceptible IR64) by the
Rapid Visco Analyzer.
In the farmers’ perception survey conducted in Ajuy, grain quality was a great
concern among respondents aside from the impacts of mixed seeds planting on disease
reduction. Also grain quality is another important criterion to measure the success of the
variety mixture in practice.
The milling quality of rice may be defined as the ability of rice grain to stand
milling and polishing without undue breakage so as to yield the greatest amount of total
recovery and the highest proportion of head rice to broken. The highest percentage of
head rice recovery was obtained from rough rice harvested in 25% R: 75% S (43.6%)
followed by 100% S (pure stand IR64) and percentage of whole grain in mixtures were
FV
97

comparable with 100% S or 100% R (pure stand Matatag 9) except for that in 75% R:
25% S (Fig. 17 and 18), indicating head rice recovery in mixtures increased with the
proportion of IR64. Head rice recovery of Matatag 9 was lower compared with IR64 thus
mixing it with IR64 improved head rice recovery in mixtures
Grain appearance is largely determined by endosperm opacity or the amount of
chalkiness either on the dorsal side of the grain (white belly), or in the center (white
center). Head rice recovery is dependent upon grain size, shape and appearance, bold and
chalky rice grain like IR5 and IR8 have low head rice recovery as compared to long,
slender and translucent rice grain like IR36 and IR42 which has high head rice recovery.
IR64 also has a high head rice recovery (Khush and Virk, 2005). Preference for grain size
and shape vary from one group of consumers to another. In Southeast Asia the demand is
for medium to medium long grains rice (Khush et al. 1979). The results have showed
milled grains from mixture treatments are long and slender rice grain and have better
grain appearance than pure stand IR64 because of high percentage with less than 10%
chalkiness. Thus, milled grain of seed mixture will be preferred by millers as well as
consumer in Southeast Asia.
In some varieties the grain tends to break more frequently at the “eye” or pit left
by the embryo when it is milled. Rice samples with damaged eyes have poor appearance
and low market value. Similarly, the greater chalkiness is equivalent to the lower market
value (Khush et al. 1979).
Many of the cooking and eating characteristics of milled rice are influenced by
the ratio and structure of two kinds of starches, amylose and amylopectin in the rice grain
98

(Sanjiva Rao et al. 1952). Amylose is the linear fraction of starch (up to 30%), whereas
amylopectin, the branched fraction, makes up the remainder of the starch (~70%).
Amylose is almost absent from the waxy (glutinous) rices. Amylose content,
gelatinization temperature, and gel consistency test indicated that mixing of IR64 with
Matatag 9 improved the cooked rice texture of Matatag 9.
A great majority of the rices from Vietnam, Thailand, Myanmar and the Indian
subcontinent have high amylose content. These rices show high volume expansion and a
high degree of flakiness. They cook dry, are less tender and become hard upon cooling.
Low amylose rices cook moist and sticky. All of the japonica varieties of temperate
regions have low amylose content. Varieties grown in the Philippines, Malaysia and
Indonesia have intermediate amylose content. Intermediate-amylose rices cook moist
and tender and do not become hard upon cooling. Intermediate amylose rices are the
preferred type in most of the rice-growing areas of the world, except where low-amylose
japonicas are grown such as Japan.
99

SUMMARY AND CONCLUSION
To characterize the resistance of Matatag 9 against rice tungro disease (RTD),
Matatag 9 and an RTD-susceptible variety IR64 were evaluated for their reactions to
tungro viruses and the insect vector (GLH). Several characteristics have been
revealed through this study. The level of RTBV resistance in Matatag 9 is weak or
due to resistance against other disease components as the number of GLH influence
the RTBV infection in Matatag 9. The relative quantification of RTBV and RTSV in
each of the varieties at different plant ages indicated that Matatag 9 can be infected
with both RTBV and RTSV and that RTBV can infect in relatively high efficiency.
Lower levels of virus infection in older plants were observed in this study, this could
be attributed to adult plant resistance involving indigenous plant defense response to
the insect and plant pathogen. Both viruses are likely to replicate in Matatag 9 using
their typical replication pathway as RTBV and RTSV are introduced into Matatag 9,
though symptom development was deterred in Matatag 9, indicating that Matatag 9
has tolerance against RTBV. On the other hand, Matatag 9 could be considered as
resistant to RTSV based on the infection rate in aged plants, though the accumulation
of RTSV in Matatag 9 is still readily detectable.
Matatag 9 was found less preferred host than IR64 by GLH for settling,
implying the contribution of antixenosis characteristics to resistance of Matatag 9.
Short adult longevity, more than 60% nymph mortality, long nymph developmental
period and low percentage of nymph becoming adult are indicative of antibiosis

effects of Matatag 9. Moreover, growth index on Matatag 9 was significantly lower
than both IR64 and TN1, while IR62 had almost same growth index value, supporting
significant involvement of antibiosis effect in resistance against RTD in Matatag 9.
101
Collectively, the results of this study strongly suggest that the resistance of
Matatag 9 is mainly due to insect resistance although the contribution of resistance
against tungro viruses in Matatag 9 cannot be ignored.
Matatag 9 and IR64 have similar agronomical characteristics, thus, Matatag 9
and IR64 can be mixed and harvested together. In the Philippines, the interplanting
approach to manage RTD was initially attempted, however, a majority of farmers
were not willing to adopt the laborious practice. Instead, the mixed seed planting was
designed.
The results of tray inoculation suggest that the mixed seed planting seems to
be more effective to reduce RTD incidence than interplanting in an area when the
disease pressure is not extremely high. Therefore, the mixed seed planting could be
recommended to the farmers as a new RTD management option when the disease
pressure is not extremely.
Possible explanation of the difference in effectiveness on disease reduction
between the two methods is the difference in spatial distribution of mixture
components. As both Matatag 9 and IR64 in the mixed seed planting are randomly
distributed, it generates an inconsistent spatial pattern that may influence the
movement and feeding behavior of insect vector. On the other hand, interplanting
provides a consistent spatial distribution of mixture components and insects may

easily to reach their preferred host in the interplanting arrangement. Thus, the random
spatial distribution of individual resistant plants was proposed as one of the potential
mechanisms for the reduction of RTD in the mixed seed planting. However, it is still
necessary to conduct a long term field trial in order to understand the mechanism of
the mixed seed planting particularly the virus-vector interaction and their ecology in
the mixture condition.
102
RTBV and RTSV can be transmitted during host selection events such as sylet
probing on plant tissue and plant fluid ingestion regardless of varieties. Also GLH can
retain RTBV and RTSV for 2-4days and 4-5 days, respectively, however, once the
insects feed on Matatag 9, they may lose their virus retention ability. Therefore,
Matatag 9 may contain certain factors which inhibit the binding between viruses and
leafhopper cuticula or suppress the activity of helper component required in the
binding between virus and cuticula at retention sites of the leafhopper.
Farmers’ perception of diseases and their understanding of pathogen ecology
are important factors that influence their adaptation of newly developed control
methods. Knowing the farmers’ perception of the mixed seed planting is necessary
for further development of technology transfer scheme to implement this new
technology effectively to farmers.
The study investigated rice farmers’ knowledge and perception of RTD and its
management and focused in detail on farmers’ perception regarding the use of mixed
seed planting of resistant and susceptible varieties for RTD management. The farmers
have relatively high awareness and knowledge of RTD and its management in Ajuy,

Iloilo, Philippines. In Ajuy main control strategies of farmers for RTD were based on
using resistant varieties and on spraying insecticide although they are aware that the
resistance may break down over time and the use of insecticide was not effective in
103
controlling RTD. Only 46% of the respondents were aware of the mixed seed planting,
however, 79% of those who were aware believed that it was effective for controlling
RTD and only 17% believed otherwise. About 70% of those who were aware had
tried mixed seed planting for 1 or 2 seasons, and more than 70% had observed its
effectiveness in controlling RTD. The low awareness of the technology “mixed seed
planting” was because it had never been introduced to the farmers, therefore, in order
for farmers to understand the features of mixed seeds planting, farmer participatory
research approach will be adequate to diffuse this new technology effectively to
farmers. After the new technology was discussed with the farmers during the forum
more than 80% of the farmers were willing to try the mixed seed planting in the
future although farmers are satisfied with their current rice quality. In addition to the
grain quality, all respondents expressed their desire to plant varieties with high eating
quality and other much IR64-like quality traits.
In the farmers’ perception survey conducted in Ajuy, grain quality was a great
concern among the respondents aside from the impacts of mixed seed planting on
disease reduction. Moreover, grain quality is another important criterion to measure
the success of the variety mixture in practice.
In general for non-waxy rice, medium and long grain varieties with clear or
translucent kernels of intermediate amylose that will remain soft even after cooking

are preferred by most consumers in the Philippines. A variety with a desirable
combination of intermediate amylose and gelatinization temperature and soft gel
consistency is IR64. Its grain quality is considered superior to that of other IR
varieties and it has been adopted widely in tropical and subtropical Asia.
104
Analysis revealed that rough rice harvested from plots planted to different
ratio of seed mixture have similar milling yield compared to the pure IR64 and
Matatag 9, the components of the mixture. Visually all samples whether from the
mixtures or from pure Matatag 9 or IR64 also look similar in terms of grain shape and
size as they were long and slender. Milled rice appearance of IR64 is chalkier than
Matatag 9 but chalkiness was reduced in seed mixtures. Rice grains from mixed seed
planting also had intermediate amylose content comparable to IR64 and they have
high intermediate to intermediate gelatinization temperature. The hardiness of the
cooked rice (consistency) of all treatments was very similar although 100% R
(Matatag 9) was a little harder and 100% S (IR64) was soft. The texture of the
mixture treatments was soft compared to 100% R but harder than 100% S. The
appearance of the cooked mixed rice (T2-T4) was very similar to 100% S (Pure IR64).
Thus, grain quality properties would not be affected when IR 64 was mixed in
different ratio with Matatag 9. Moreover, mixing of IR64 with Matatag 9 improved
the cooked rice texture of Matatag 9 and farmers in tungro endemic areas could plant
mixed seeds of susceptible IR64 with resistant Matatag 9 and be assured of grain
quality comparable to IR 64, the most preferred variety by rice millers and consumers
in the Philippines

RECOMMENDATIONS
1. Further study is necessary to investigate the RTSV resistance in Matatag 9.
2. Rice variety that has only insect resistance could be used as a (R) mixture
component as long as it has similar agronomical characteristic and grain quality as
the commercial but RTD susceptible component.
3. Mixed seed planting could be recommended to the farmers as a new RTD
management option when the disease pressure is not extremely high though it is
still necessary to conduct a long term field trial in order to understand the
mechanism of the mixed seed planting particulary the virus-vector interaction and
their ecology in the mixture condition.
4. Farmer participatory research approach is necessary to diffuse this new
technology effectively to farmers in order to understand the features of mixed
seeds planting.
5. Since rice grains from mixed seed planting of Matatag 9 and IR64 have similar
milling yield, physical attributes, and physicochemical characteristics with the
pure IR64 and improved the cooked rice texture of Matatag9, farmers in RTD-
endemic areas could plant mixed seed of susceptible IR64 with resistant Matatag
9 and be assured of grain quality comparable to IR64 and still manage RTD.

LITERATURE CITED
ABADIE, C., V. EDEL and C. ALABOUVETTE. 1998. Soil suppressiveness to
Fusarium wilt: Influence of a cover plant on density and diversity of Fusarium
populations. Soil Biol. Biochem. 30:643-649.
ALBAR, L, M. N. NDJIONDJOP, Z. ESSHAK, A. BERGER, A. PINEL, M. JONES, D.
FARGETTE and A. GHESQUIERE. 2003. Fine genetic mapping of a gene
required for rice yellow mottle virus cell-to-cell movement. Theor. Appl. Genet.
107:371-378.
ANGELES, E. R., R. C. CABUNAGAN, E. R. TIONGCO, O. AZZAM, P. S. TENG, G.
S. KHUSH and T. C. B. CHANCELLOR. 1998. Advanced breeding lines with
resistance to rice tungro viruses. Int. Rice. Res. Notes 23:17-18.
ANJANETULU, A. 1996. Rice tungro resistance – a concept. Central Rice Research
Institute Cuttack 753006, Orissa, India. 23pp.
ANONYMOUS. 1994. Instituting preventive and eradication measures against the tungro
virus in rice. Philippine Department of Agriculture Memorandum Circular No.3.
2p.
ASHIZAWA, T., K. ZEMBAYASHI and S. KOIZUMI. 1999. Effect of partial resistance
on rice blast control with cultivar mixture. Phytopathology 89:
AUTRIQUE, A and M. J. POTS. 1987. The influence of mixed cropping on the control
of potato bacterial wilt. Ann. Appl. Biol. 111:125-133.
AZZAM, O and T. C. B. CHANCELLOR. 2002. The biology, epidemiology, and
management of rice tungro disease in Asia. Plant Dis. 86:88-100.
AZZAM, O., R. C. CABUNAGAN and T. C. B. CHANCELLOR. 2000. Methods for
Evaluating Resistance to Rice tungro Disease. Discussion Paper. IRRI. 38: 22-23.

108
BARIA, A. R. 1993. Status of rice tungro disease in the Philippines: a guide to current
and future research. Epidemiology and Management of Rice tungro disease.
Natural Resources Institute. 76-83.
BAJET, N. B., R. D. DAQUIOAG and H. HIBINO. 1985. Enzyme-linked
immunosorbent assay to diagnose rice tungro. J. Plant Prot. Trop. 2: 1125-129.
BAJET, N. B., V. M. AGUIERO, G. B. JONSON, R. C. CABUNAGAN, E. M.
MESINA and H. HIBINO. 1986. Occurrence and spread of rice tungro spherical
virus in the Philippines. Plant Dis. 70:971-973.
BACKUS, E. A. 1985. Anatomical and sensory mechanisms of leafhopper and
planthopper feeding behavior. In: The leafhoppers and Planthoppers. Eds.L. R.
Nault and J. G. Rodriguez. New York: Wiley. P163-194
BENTLEY, J. W and G. N. THIELE. 1999. Bibliography: Farmer knowledge and
management of crop disease. Agriculture and Human Values 16:75-81.
BROWN, J. F. 1975. Factors affecting the relative ability of strains of fungal pathogens
to survive in populations. J. Auster. Inst. Agric. Sci. 41: 3-11.
BROWNING, J. A. 1974. Relevance of knowledge about natural ecosystems to
development of pest management programs to agroecosystems. Proc. Am.
Phytopathol. Soc. 1:191-199.
BROWNING, J. A. 1989. Current thinking on the use of diversity to buffer small grains
against highly epidemic and vulnerable foliar pathogens: problems and future
prospects. In Breeding strategies for resistance to the rust of wheat, pp. 76-90.
EDS N W SIMMONDS and S RAJARAM. Mexico DF: CIMMYT.
BONMAN, J. M., B. A. ESTRANDA and R. I. DENTON. 1986. Blast management with
upland rice cultivar mixtures. In Proceedings of the 1985 Jakarta conference:
progress in upland rice research, 375-382. Los banos, Philippines: International
Rice Research Institute.

BOZEMAN, N. 2000. Technology transfer and public policy: a review of research and
theory. Research Policy 29:627-655.
BURDON, J. J. 1987. Disease and plant population biology. Cambridge: Cambridge
University Press.
BURDON, J. J and G. A CHIVERS. 1976. Epidemiology of Pythiuminduced dampingoff
in mixed species seedling stands. Ann. Appl. Biol. 82:233-240.
BURDON, J. J and R. C. SHATTOCK. 1980. Disease in plant communities. Appl. Biol.
5: 145-219.
CABAUATAN, P. Q and H. HIBINO. 1988. Isolation, Purification, and Serology of Rice
Tungro Bacilliform and Rice Tungro Spherical Viruses. Plt. Dis. 72 (6): 526-528
109
CABAUATAN, P. Q., R. C. CABUNAGAN and H. KOGANEZAWA. 1995.
Biological variants of rice tungro viruses in the Philippines. Phytopathology
85:77-81.
CABUNAGAN, R. C and H KOGANEZAWA. 1993. Geographical distribution of
resistant varieties to rice tungro disease (RTD). Int'l Rice Res. Notes 18:21.
CABUNAGAN, R. C and I. R. CHOI. 2005. Rice tungro disease incidence in mixed
planting of resistant and susceptible rice varieties. Phil Journal of Crop Science
30(1):84.
CABUNAGAN, R. C., Y. SHIBATA, and I. R. CHOI. 2004. Varietal mixture: a strategy
for sustainable management of rice tungro disease. Proc. World Rice Research
Congress, 5-7 November, 2004, Tsukuba, Japan.
CABUNAGAN, R. C., H. HIBINO, S. SAMA and S. A. RIZVI. (1987). Resistance of
rice plants to Nephotettix virescens in relation to rice tungro- associated viruses
pp. 66-76. In: Proc. of the Workshop on Rice Tungro Virus. 24-27 September
1986, Maros, South Sulawesi Indonesia. Indonesia Ministry of Agriculture.

110
CABUNAGAN, R. C., FLOREZ, Z. M., E. C. COLOQUIO and H. KOGANEZAWA.
1993. Virus detection in varieties resistant / tolerant to tungro. Int. Rice Res.
Notes 18: 22-23.
CABUNAGAN, R. C., E. R. ANGELES, E. R. TIONGCO, S. VILLAREAL, X. H.
TRUONG, I. G. N. ASTIKA, A. MUIS, A. K. CHOWDHURY, T. GANPATHY,
T. C. B. CHANCELLOR, P. S. TENG and G. S. KHUSH. 1996. Evaluation of
rice germplasm for resistance to rice tungro disease. In: Rice Tungro Disease
Epidemiology and Vector Ecology. T.C.B. Chancellor, P.S. TENG and K.L.
HEONG (eds.). IRRI. pp. 67-70.
CABUNAGAN, R. C., E. R. ANGELES, S. VILLAREAL, O. AZZAM, P. S. TENG, G.
S. KHUSH, T. C. B. CHANCELLOR, E. R. TIONGCO, X. H. TRUONG, S.
MANCAO, I.G.N. ASTIKA, A. MUIS, A.K. CHOWDHURY, V.
NARASIMHAN, T. GANPATHY and N. SUBRAMANIAM. 1999.
Multilocation evaluation of advance breeding line for resistance to rice tungro
viruses. In: Rice tungro disease management. Chancellor, T.C.B., O. Azzam and
K.L. Heong (Eds.). Proceedings of International Workshop on Tungro Disease
Management, 9-11 November 1998. Los Baños, Laguna, Philippines: Int. Rice
Res. Inst. pp. 45-57.
CABUNAGAN, R. C., CASTIILA, N., COLOQUIO, E. L., TIONGCO, E. R., TRUONG,
X. H., FERNANDEZ, J., Du, M. J., ZARAGOSA, B., HOZAK, R. R., SAVARY,
S and AZZAM. O. 2001. Synchrony of planting and proportion of susceptible
varieties affect rice tungro disease epidemics in the Philippines. Crop Prot. 20:
499-510.
CAGAMPANG, G. B., C. M. PEREZ, and B. O. JULIANO. 1973. A gel consistency test
for eating quality of rice. J Sci Food Agric 24:1589-1594
CARRINGTON, J. C., K. D. KASSCHAU, S. K. MAHAJAN, and M. C. SCHAAD.
1996. Cell-to-cell and long distance transport of viruses in plants. Plant Cell
8:1669-1681.
CHANCELLOR, T. C. B. 1996. Leafhopper Ecology and Rice Tungro Disease Dynamics.
In: Rice Tungro Disease Epidemiology and Vector Ecology. T.C.B. Chancellor,
P.S. TENG, and K.L. HEONG (Eds.) IRRI. 67-70.

CHANCELLOR, T. C. B and J. M. THRESH. (eds). 1997. Epidemiology and
Management of Rice Tungro Disease , UK : Natural Resources Institute .
111
CHANCELLOR, T. C. B., A. G. COOK and K. L. HEONG, 1996. The within-field
dynamics of rice tungro disease in relation to the abundance of its major
leafhopper vectors. Crop Prot. 15(5):439-449.
CHANCELLOR, T. C. B., K. L. HEONG, A. G. COOK and S. VILLAREAL. 1996.
Leafhopper Ecology and Rice Tungro Disease Dynamics. Rice Tungro Disease
Epidemiology and Vector Ecology. IRRI. 10-35
CHEN, Y. M. and A. T. JALIL. 1997. Incidence and control of rice tungro disease in
Malysia pp. 103-108. In: Epidemiology and management of rice tungro disease.
T.C.B. Chancellor and J. M. THRESH (Eds). NRI. 106 p.
CHIN, K. M and A. N. HUSIN, 1982. Rice variety mixtures in disease control. Proc. Int.
Conf. Plant Prot. Trop. pp. 241-246.
CHOWDHURY, A. K., P. S. TENG and H. HIBINO. 1990. Production of helper
component in rice tungro virus (RTSV)-infected plants. Int. Rice Res. Nwesl.
15:14.
CHOWDHURY, A. K., H. HIBINO and P. S. TENG. 1994. Dispersal of rice tungro
associated viruses by leafhoppers in the presence of singly or jointly infected
source plants under caged condition. Proc. Indian National Science Academy.
Part B. Biological Society. 68:281-286. Dept. of Plant Pathology, west Bengal,
India.
DAHAL, G., H. HIBINO., R. C. CABUNAGAN, E. R. TIONGCO., Z. M. FLORES and
V. M. AGUIERO. 1990a. Changes in cultivar reactions to tungro due to changes
in the “virulence” of the leafhopper vector. Phytopathology 80:659-665.
DAHAL, G., H. HIBINO and R. C. SAXENA. 1990b. Association of leafhopper feeding
behavior with transmission of rice tungro to susceptible and resistant rice cultivars.
Phytopathology 80: 371-377.

DIXON, A. F. G. 1985. Aphid ecology. Blackie and Sons. London.
112
ESCALADA, M. M and K. L HEONG, 1997. Methods for research on farmers’
knowledge, attitudes, and practices in pest management. In: K.L. HEONG and
M.M. ESCALADA (eds), Pest Management Practices of Rice Farmers in Asia.
IRRI, Los Baños, Philippines.
FINCKH, M. R and C. C. MUNDT. 1992. Stripe rust, yield, and plant cmpetition in
wheat cultivar mixtures. Phytopathology 82: 905-913.
FINCKH, M. R and M. S. WOLFE. 1997. The use of biodiversity to restrict plant
diseases and some consequences for farmers and society. In: Jakson, L.E. ed.
Ecology in Agriculture. San Diego: Academic Press. 193-233.
FINCKH, M. R., E. S. GACEK, H. S. CZEMBOR and M. S. WOLFE. 1999. Host
frequency and density effects on powdery mildew and yield in mixtures of barley
cultivars. Plant Pathol. 48: 807-816.
FINCKH, M. R., E. S. GACEK, H. GOYEAU, C. LANNOU, U. MERZ, C. C. MUNDT,
L. MUNK, J. NADZIAK, A. C. NEWTON, C. DE VALLAVIELLE-POPE and
M. S. WOLFE. 2000. Cereal variety and species mixtures in practice with
emphasis on disease resistance. Agronomie 20: 813-837.
FRASER, R. S. S. 1990. The genetics of resistance to plant viruses. Annu. Rvw.
Phytopathol. 28:179-200.
FRASER, R. S. S. 2000. Special aspects of resistance to viruses. In: Mechanisms of
resistance to plant diseases. EDS. SLUSARENKO, A. J., FRASER, R. S. S. and
VAN LOON, L.C. Kluwer Academic Publishers. Netherlands. pp. 479-520
GARRETT, K. A and C. C. MUNDT. 1999. Epidemiology in mixed host populations.
Phytopathology 89:984-990.

113
GENO, L and B.GENO. 2001. Polyculture production. Principles, benefits and risks of
multiple cropping land management systems for Australia. Rural Industries
Research and Development Corporation, Barton, Australia.
GIBBS, A and B. HARRISON. 1976. Plant Virology: The Principles. John Wiley and
Sons. 285p
HARIRI, D., M. FOUCHARD and H. PRUD’HOMME. 2001. Incidence of soil-borne
wheat mosaic virus in mixtures of susceptible and resistant wheat cultivars. Eur. J.
Plant. Pathol. 107: 625-631.
HARLAN, J. R. 1976. Disease as a factor in plant evolution. Annu. Rev. Phytopathol. 14:
31-51.
HASANUDDIN, A and H. HIBINO. 1989. Grain yield reduction, growth retardation,
and virus concentration in rice plants infected with tungro-associated viruses. In
Crop Losses due to Disease Outbreaks in the Tropics and Countermeasures. Trop.
Agric. Res. Series No. 22. pp. 56-73.
HASANUDDIN, A., I. N. WIDIARTA and YUDIANTO. 1999. Improving IPM
technology for rice tungro disease in Indonesia. pp. 129-1377 In: Rice tungro
disease management. T.C.B. Chancellor, O. Azzam and K. L. Heong (eds). IRRI.
166 p.
HASANUDDIN, A., P. KOESNANG and H. HIBINO. 1997. Rice tungro virus disease in
Indonesia: present status and current management strategy. 64 p. In:
Epidemiology and management of rice tungro disease. T.C.B. Chancellor and J.
M. Thresh (eds). NRI. 106 p.
HEONG, K. L., ESCALADA, M. M and V. O. MAI. 1994. An analysis of insecticide use
in rice: case studies in the Philippines and Vietnam. International Journal of Pest
Management. 40: 173-178.
HIBINO, H. 1983. Transmission of two rice tungro-associated viruses and rice waika
virus from doubly or singly infected source plants by leafhopper vectors. Plant
Dis. 67: 774 -777.

114
HIBINO, H. 1995. Rice tungro-associated viruses and their relationships to host plant and
vector leafhoppers. In Pathogenesis and Host Specificity in Plant Diseases,
Histopathological, Biochemical, Genetic and Molecular Bases. Vol.Ⅱ Viruses and
Viroids, ed. P.R. Singh, U.S. Singh, K. Khomoto, pp.393-403. Oxford:Elsevier
HIBINO, H and P. Q. CABAUATAN. 1987. Infectivity neutralization of rice tungroassociated
viruses acquired by vector leafhoppers. Phytopathology 77: 473-476.
HIBINO, H and R. C. CABUNAGAN. 1986. Rice tungro-associated viruses and their
relations to host plants and vector leafhoppers. Trop. Agric. Res. Ser. 19: 173-182.
HIBINO, H., M. ROECHAN and S. SUDARISMAN. 1978. Association of two types of
virus particles with penyakit habang (tungro disease) of rice in Indonesia.
Phytopathology 68: 1412-16.
HIBINO, H., N. SALEH and M. ROECHAN. 1979. Transmittion of two kinds of rice
tungro-associated viruses by insect vectors. Phytopathology 69: 1266-1268.
HIBINO, H, E. R. TIONGCO, R. C. CABUNAGAN and Z. M. FLORES. 1987.
Resistance to rice tungro-associated viruses in rice under experimental and natural
conditions. Phytopathology 77:871-875.
HIBINO, H., R. D. DAQUIOAG, P. Q. CABAUATAN and G. DAHAL. 1988.
Resistance to rice tungro spherical virus in rice. Plant Dis. 72:843-847.
HIBINO, H., R. D. DAQUIOAG, E. M. MESINA and V. M. AGUIERO. 1990.
Resistances in rice to tungro-associated viruses. Plant Dis. 74(11): 923-926.
HIDDINK, G. A., A. J. TERMORSHUIZEN, J. M. RAAIJMAKERS and A. H. C. VAN
BRUGGEN. 2005. Effect of Mixed and Single Crops on Disease Suppressiveness
of Soils. Phytopathology. 95: 1325-1332.

115
HIMES, R. S. 1971. Tagalog concepts of causality: disease. IN LYNCH F, A. DE
GUZMAN, editors. Modernization: its impact in the Philippines. Vol. V. Institute
of Philippines Culture Paper No. 10. Quezon City: Ateneo de Manila University.
HOLT, J., T. C. B. CHANCELLOR, D. R. REYNOLDS and E. R. TIONGCO. 1996.
Risk assessment for planthopper and tungro disease outbreaks. Crop. Prot. 15:
359-.368.
HULL, R. 1996. Molecular biology of rice tungro viruses. Annu. Rev. Phytopathol. 34:
275-297.
HULL, R. 2002. Matthew’s Plant Virology. New York: Academic Press. 1001 p.
IMBE, T, R. IKEDA, N. KOBAYASHI, L. A. EBRON, R. R. YUMOL, N. S.
BAUTISTA and RE TABIEN. 1995. Genetic studies in relation to breeding rice
varieties resistant to tungro disease. IRRI-GOVERNMENT OF JAPAN
COLLABORATIVE RESEARCH PROJECT. pp. 3-67.
INGER GENETIC RESOURCES CENTER. 1996. Standard evaluation system for rice.
4 th edition. Los Baños, Laguna, Philippines. IRRI. 52p.
JOHN, V. T. 1968. Identification and characterization of tungro, a virus disease of rice
in India. Plt. Dis. Reptr. 52:871-875.
JULIANO, B. O. 1971. A simplified assay for milled-rice amylase. Cereal Sci. Today
16:334-338,340,360.
JULIANO B. O and B. DUFF, 1991. Rice grain quality as an emerging priority in
national rice breeding programs. In: Rice Grain Marketing and Quality Issues
p55-64 IRRI, Los Baños, Laguna.
KAWABE, S and D. L. MCLEAN. 1980. Electronic measurement of probing activities
of the green leafhopper of rice. Entomol. Exp. & Appl. 27: 77-82.

116
KELLER, K. E., I. E. JOHANSEN, R. R. MARTIN and R. O. HAMPTON. 1998.
Potyvirus genome linked protein (VPg) determine pea seed borne mosaic virus
pathotype specific virulence in Pisum sativum. Mol. Plt. Micro. Inter. 11:124-130.
KELLER, B., C. FEUILLET and MESSMERM. 2000. Genetics of disease resistance.
Basic concepts and application in resistance breeding. In: Mechanisms of
resistance to plant diseases. Eds. Sluzarenko, A. J., Fraser, R. S. S. and van Loon,
L.C. Kluwer Academic Publishers. Netherlands. pp. 101-160.
KENMORE, P. E. 1991. Indonesia’s Integrated Pest Management-a Model for Asia
(Manila: FAO Intercountry IPC Rice Programme).
KOBAYASHI, N and R. IKEDA. 1992. Necrosis caused by rice tungro viruses in Oryza
glaberrima and O. barthii. Japan. J. Breed. 42 : 885-890
KOGANEZAWA, H. 1998. Present status of controlling rice tungro virus. In: Plant Virus
Disease Control, A. Hadidi, R. K. Khetarpal, and H. Koganezawa, eds. Plant
Virus Disease Control, American Phytopathological Society, USA, pp 459-469.
KOGANEZAWA, H and R. C. CABUNAGAN. 1997. Resistance to rice tungro virus
rice disease. In Chancellor, T. C. B. and J. M. THRESH (eds.). Epidemiology and
management rice tungro disease. Chatham, UK: Natl. Resource Inst. pp. 54-59.
KOLSTER, P. L. MUNK and O. STOLEN. 1989. Disease severity and grain yield in
barley multilines with resistance to powdery mildew. Crop Science 29: 1459-1463.
KONDAIAH, A., A. V. RAO and T. E. SRINIVASAN. 1976. Factors favoring spread of
rice tungro disease under field conditions. Plt. Dis. Reptr. 60: 803-806.
KHUSH G. S. 1977. Disease and insect resistance in rice. Adv. Agrom. 29: 265-341.
KHUSH G. S. 1997. Origin, dispersal, cultivation and variation of rice. Plant Molecular
Biology. 35: 25-34.

KHUSH, G. S and S. VIRMANI. 1985. Breeding rice for disease resistance. pp. 239-279.
In: G. E. Russel (ed). Progress in Plant Breeding. London Butterworths.
117
KHUSH G. S and P. VIRK, 2005. IR Varieties and Their Impact. IRRI, Los Baños,
Laguna. B. HARDY, eds. International Rice Research Institute, Manila,
Philippines.
KHUSH G. S., C. M PAULE, and N. M. DE LA CRUZ. 1979. Rice grain quality
evaluation and improvement at IRRI. In: Proc. of the Workshop on Chemical
Aspects of Rice Grain Quality, pp21-31, IRRI, Los Baños, Laguna
KHUSH, G. S., E. ANGELES, P. S. VIRK and D. S. BRAR. 2004. Breeding rice for
resistance to tungro virus at IRRI. SABRAO Journal of Breeding and Genetics
36(2): 101-106
KISHINO, K and Y. Ando. 1978. Insect resistanceof rice plant to the green rice
leafhopper Nephotettix cincticeps UHLER. 1. Laboratory technique for testing the
antibiosis. Jpn. J. Appl. Entomol. Zool. 22: 169-177 (in Japanese with English
summary).
LAMEY, H. A, P. SURIN and J. LEEUWANGH. 1967. Transmission experiments on
the tungro virus in Thailand. Int. Rice Comm. Newsl. 16:16-19.
LAPIS, D. B. 1991. The incidence of rice tungro and some contributory factors for its
outbreaks in the Philippines. In: Proc. National Conference and Workshop on
Integrated Pest Management in Rice, Corn and Selected Major Crops, p. 87-93,
College, Laguna, National Crops Protection Center, UPLB.
LEUNG, H., Y. ZHU, I. R. MOLINA, J. X. FAN, H. CHEN, I. PANGGA, C. VREA
CRUZ and T. W. Mew. 2003. Using genetic biodiversity to achieve sustainable
rice disease management. Plant Dis. 87:1156-1169.
LING, K. C. 1972. Rice virus disease. Internatinal Rice Res. Inst. P.O. Box 933, Manila,
Philippines, 142 Pages.

LING, K. C and E. R. TIONGCO. 1979. Rice virus disease in the Philippines.
Internatinal Rice Res. Inst. Philippines
LITSINGER, J. A. 1989. Second generation insect pest problems on high-yielding rices.
Trop. Pest. Mgt. 35:235-242.
LITTLE, R. R., G. B. HILDER and E. H. DAWSON. 1958. Differential effect of dilute
alkali on 25 varieties of milled white rice. Cereal Chem 35:111-126.
118
LIU, L and S. TAKAHASHI. 1990. Evaluation of host susceptibility to the green
leafhopper, Nephotettix spp. (Homoptera: Cicadellidae) by defferent criteria. Appl.
Entomol. Zool. 25: 49-57
LOEVINSOHN, M. E. 1984. The Ecology and Control of Rice Pests in Relation to the
Intensity and Synchrony of Cultivation. PhD Thesis. University of London.
London, UK.
MACLEAN, J. L., D. C. DAWE, B. HARDY and G. P. HETTEL. (eds.). 2002. Rice
Almanac: Source Book for the Most Important Economic Activity on Earth, Third
edition. International Rice Research Institute, Los Baños, Laguna, Philippines;
West African Rice Development Association, Bouaké, Côte d’Ivoire; Centro
International de Agricultura Tropical (International Center for Tropical
Agriculture), Cali, Colombia; Food and Agriculture Organization, Rome, Italy.
MAYO, M. A and C. R. PRINGLE. 1998. Virus taxonomy-1997. J GEN VIROL. 79:
649-657
MERCA F. E., T. M. MASAJO and A. D. BUSTRILLOS. 1978. Rice grain quality
evaluation in the Philippines. Paper presented at the Workshop on Chemical
Aspects of Grain Quality, 7 pp, IRRI, Los Baños, Laguna.
MUNDT, C. C and J. A. BROWNING. 1985. Development of crown rust epidemics in
genetically diverse oat populations: Effect of genotype unit area. Phytopathology
75:607-610.

119
MUNDT, C. C and K. J LEONARD. 1985. Effect of host genotype unit area on epidemic
development of crown rust following focal and general inoculations of mixtures
of immune and susceptible oat plants. Phytopathology 75:1141-1145.
MUNDT, C. C and K. J. LEONARD. 1986. Analysis of factors affecting disease increase
and spread in mixtures of immune and susceptible plants in computer-simulated
epidemics. Phytopathology 76: 832-840.
MUNDT, C. C. 2002. Use of multilane cultivars and cultivar mixtrures for disease
management. Annu. Rev. Phytopathol. 40:381-410
NAGARAJU, N., H. M. VENKATESH, H. WARBURTON, V. MUNIYAPPA, T. C. B.
CHANCELLOR and J. COLVIN. 2002. Farmers’ perception and practices for
managing tomato leaf curl virus disease in Southern India. International Journal of
Pest Management 48:333-338.
NELSON, R., R. ORREGO, O. ORTIZ, J. TENORIO, C. C. MUNDT, M. FREDRIX and
N. V. VIEN. 2001. Working with resource-poor farmers to manage plant diseases.
Plant Dis. 85:684-695.
NISHI, Y, T. KIMURA and I. MAEJIMA. 1975. Causal agent of waika disease of rice
plant in Japan. Ann. Phytopathol. Soc. Japan 41:223-227.
OTHMAN, A. B., M. J. AZIZAH and A. T. JATIL. 1999. Surveillance scheme for
tungro forecasting in Malaysia. In: Chancellor, T. C. B., O. Azzam and K. L.
Heong (eds.). Rice tungro disease management. Proceedings of International
Workshop on Tungro Disease Management, 9-11 November 1998. Los Baños,
Laguna, Philippines: Int. Rice Res. Inst. pp. 85-92.
PEDROSO, J. P. 2001. Epidemiology of tungro disease in pure and mixed stands of rice
cultivars (Oryza sativa Linn.) with different types of resistance. PhD thesis.
University of the Philippines, Los Baños, Laguna, Philippines.
PYNDJI, M. M and P. TRUTMANN. 1992. Managing angular leaf spot on common bean
in Africa by supplementing farmer mixtures with resistant varieties. Plant Disease
76: 1144-1147.

120
POWER, A. G. 1990. Croping systems, insect movement, and the spread of insecttransmitted
diseases in crops. In Agroecology, ed. SR Gliessman, pp.47-69. New
York: Springer-Verlag
POWER, A. G. 1991. Virus spread and vector dynamics in genetically diverse plant
populations. Ecology 72:232-41
PRETTY, J. 1995. Regenerating agriculture. Policies and practices for sustainability and
self-reliance. Earthscan Publications Ltd., London.
RAO, G. M and A. ANJANEYULU. 1978. Host range of rice tungro virus. Plant Dis.
Rep. 62: 955-957.
RHOADES, R. E and R. H. BOOTH. 1982. Farmer back to farmer: A model for
generating acceptable agricultural technology. Agric. Admin. 11:127-137.
RIVERA, C. T and S. H. OU. 1965. Leafhopper transmission of “tungro” disease of rice.
Plt. Dis. Reptr. 49:127-131.
ROLA, A. C and P. L. PINGALI., 1993. Pesticides, Rice Productivity and Farmers’
Health: An Economic Assessment (Washington, DC: World Resources Institute
and Los Banos, Philippines: International Rice Research Institute).
SAMA, S., A. HASANUDDIN, I. MANWAN, R. C. CABUNAGAN and H. HIBINO.
1991. Integrated management of rice tungro desiease in South Sulawesi,
Indonesia. Crop Protection, 10: 34-40.
SAJIVA RAO B, A. R.VASUDEV and R. S. SUBRAHMANYA. 1952. The amylase and
amylopectin content of rice and their influence on the cooking quality of cereals.
Proc. Indian Acad. Sci. 368:70-80.
SATAPATHY, M. K., T. C. B. CHANCELLOR, P. S. TENG., E. R. TIONGCO., J. M.
THRESH. 1997. Effect of introduced sources of inoculum on tungro disease
spread in different varieties. pp 11-21. In: Epidemiology and Management of Rice
Tungro Disease. T. C. B. Chancellor and J. M. Thresh (eds). NRI. UK.

SATAPATHY, M. K and A. ANJANEYULU. 2001. Rice Tungro Disease Epidemic-An
Analysis. Discovery Publishing House.
121
SAVARY, S., N. FABELLAR, E. R. TIONGCO and P. S. TENG. 1993. A
characterization of rice tungro epidemics in the Philippines from historical survey
data. Plant Dis 77:376-382.
SAXENA, K. N., J. R. GANDHI and R. C. SAXENA. 1974. Patterns of relationship
between certain leafhoppers and plants. I. responses to plants. Entomol. Exp. Appl.
17: 303-318
SELENER, D. 1997. Participatory Action Researchand Social Change. Cornell
Participatory Action Research Network, Cornell University. Ithaca, NY.
SERRANO, F. B. 1957. Rice accep na pula or stunt disease- severe menace to the
Philippines rice industry. Philipp J. Crop Sci. 86: 203-223
SHEN, P., M. KANIEWSKA., C. SMITH and R. N. BEACHY. 1993. Nucleotide
sequence and genomic organization of rice tungro apherical virus. Virology 193:
621-630.
SHINKAI, A. 1977. Rice waika, a new virus disease, and problems related to its
occurrence and control. Jpn. Agric. Res. Q. 11: 151-55
SHUKLA, V. D and A. ANJANEYULU. 1981a. Spread of tungro viruse disease in
different ages of rice crop. J. Plt Dis. Prot. 88: 614-620.
SHUKLA, V. D and A. ANJANEYULU. 1981b. Adjustment of planting date to reduce
rice tungro disease. Plt Dis. 65: 409-411.
SHUKLA, V. D and A. ANJANEYULU. 1981c. Plant spacing to reduce rice tungro
disease. Plt Dis. 65: 584-586.
SLOVIC, P. 1987. Perception of risk. Science 236: 280-288.

SMITHSON, J. B and J. M. LENNE. 1996. Varietal mixtures: a viable strategy for
sustainable productivity in subsistence agriculture. Ann. Appl. Boil. 128:127-158.
SOGAWA, K. 1976. Rice tungro virus and its vectors in tropical Asia. Rev. Plt. Prot.
Res. 9:21-46.
STA CRUZ, F. C., H. KOGANIZAWA and H. HIBINO. 1993. Comparative cytology of
rice tungro viruses in selected rice cultivars. J. Phytopathol. 138:274-282
122
STA CRUZ, F. C., R. HULL and O. AZZAM. 2003. Changes in level of virus
accumulation and incidence of infection are critical in the characterization of rice
tungro bacilliform virus (RTBV) resistance in rice. Arch. Virol. 148:1465-1483.
SUZUKI, Y., G. N. ASTIKA, K. R. WIDRAWAN, G. N. GEDE, N. RAGA and
SOEROTO. 1992. Rice tungro disease vectored by the green leafhopper: Its
epidemiology and forcasting technology. Jap. Agric. Res. Q. 26: 98-104.
TAKAHASHI, Y., E. R. TIONGCO, P. Q. CABAUATAN, H. KOGANEZAW, H.
HIBINO and T. OMURA. 1993. Detection of rice tungro bacilliform virus by
polymerase chain reaction for assessing mild infection of plants and viruliferous
vector leafhoppers. Phytopathol. 83:655-659.
THRESH, J. M. 1976. Gradient of plant virus diseases. Ann. Appl. Biol. 82: 381-406.
THRESH, J. M. 1982. Cropping practices and virus spread. Annu. Rev. Phytopathol.
20:193-218.
TIONGCO, E. R., R. C. CABUNAGAN, Z. M. FLOREZl, H. HIBINO and H.
KOGANEZAWA. 1993. Serological monitoring of rice tungro disease
development in the field: its implication in disease management. Plant Dis. 77:
877-881
TRENBATH, B. R. 1975. Diversity or be damaged? Ecologist 5: 76-83.

123
TRUONG, X. H., E. R. TIONGCO, E. H. BATAY-AN, S. C. MANCAO, M. J. OU and
N. A. JUGUAN. 1999. Rice tungro disease in the Philippines. pp 9-10. In Rice
tungro disease management. Chancellor, T.C.B., O. AZZAM and K.L. HEONG
(eds.). Proceedings of International Workshop on Tungro Disease Management,
9-11 November 1998. Los Baños, Laguna, Philippines: Int. Rice Res. Inst. 106
pp.
VALKONEN, J. P. T. 2002. Natural resistance to viruses. In Khan, J. A. and J. Dijkstra
(eds.). Plant Viruses as Molecular Pathogens. New York: Food Products Press.
pp. 367-397.
VILICH, V. 1993. Crop rotation with pure stands and mixtures of barley and wheat to
control stem and root rot diseases. Crop Prot. 12:373-379.
WARBURTON, H., F. L. PALIS and S. VILLAREAL. 1997. Farmers, perceptions of
rice tungro disease in the Philippines. In: K.L. Heong and M.M. Escalada (eds)
Pest Management Practices of Rice Farmers in Asia. IRRI, Los Baños,
Philippines.
WOLFE, M. S. 1984. Trying to understand and control powdery mildew. Plant Pathology
33: 451-466
WOLFE, M. S. 1985. The current status and prospects of multilane cultivars and variety
mixtures for disease resistance. Annual Review of Phytopathology 23:251-273.
WOLFE, M. S., J. A. BARRETT, J. E. E. JENKINS. 1981. The use of cultivar mixtures
for disease control. In: Strategies for control of cereal diseases, pp. 73-80. (eds). J.
F. Jenkyn and R. T. Plumb. Oxford: Blackwell.
ZHU, Y., H. CHEN, J. FAN, Y. WANG, Y. LI, J. CHEN, J. X. FAN, S. YANG, L. HU,
H. LEUNG, T. W. MEW, P. S. TENG, Z. WANG and C. C. MUNDT. 2000.
Genetic diversity and disease control in rice. Nature 406:718-722.

Appendix 1. Questions for socioeconomic survey in Ilo-ilo.
A. Participants’ Profile
1) Name_______________________________Age_____________
2) Marital Status ( ) Single ( ) Married
3) Number of Children_____ Number of household members ______
4) Education
( ) Elementary graduate
( ) High School graduate
( ) College graduate
( ) No education
5) Land Ownership ( ) Owner ( ) Tenant ( ) Share Holder
6) Size of farm area:________________Hectares
7) Size of area planted to rice_________Hectares
B. Farm Profile
1) How long have you been farming? _________Years
2) Are you a commercial or self sustaining farmer?
( ) Commercial (Sells harvest)
( ) Self sustaining (Produce for family consumption only)
3) Average gross income per year from rice farm ______P
4) Average rice yield per season
WS________Cavans of 50 Kg
DS_________Cavans of 50 Kg
5) Name of varieties planted for the past 4 seasons
________________ _________________
________________ _________________
6) Where did you acquire the varieties you planted?
( ) Seed grower ( ) DA office ( ) Research Station
( ) Other farmers ( ) Other Sources____________
7) Common insect problems in your rice farm
________________ _________________
________________ _________________
8) Common disease problems in your rice farm
________________ _________________
________________ _________________
9) Rank the importance of the following insect and disease problems in rice: 1, 2, 3, 4
and 5 with, 1 as most important and 5 the least important
( ) Stemborer ( ) Rice blast
( ) BPH ( ) Bacterial leaf blight
( ) Rice bug ( ) Tungro

( ) Leaf folders ( ) Sheath blight
( ) Cut worms ( ) Bacterial leaf streak
C. Awareness of tungro disease
1) Are you aware of tungro disease? ( ) Yes ( ) No
2) Have you had tungro disease in your rice farm ( ) Yes ( ) No
3) For past 5 years how many times did you have tungro in your rice
farm?________Times
4) How serious was the damage of tungro in your farm? _____ Rank 1 to 3: with, 1 as
most serious; 2 moderately and 3 as least serious
5) What do you think causes tungro disease?
( ) Poor soil ( ) Poor water ( ) Poor seeds ( ) Fungi ( ) Bacteria
( ) Virus ( ) Insects ( ) Others ____________
6) What spread tungro disease?
( ) Water ( ) Seeds ( ) Wind ( ) Brown planthopper
( ) Green leafhopper ( ) Others _______________
7) How do you distinguish tungro from other diseases?
( ) Change of leaf color ( ) Height reduction
( ) Presence of green leafhopper
D. Awareness of tungro disease control
1) How do you control tungro in your rice field?
( ) Spray pesticides. What pesticides? ___________________
( ) Use of resistant varieties. What varieties? ______________
( ) Removal of infected plants. ( ) Others______________
2) Do you think tungro could be controlled with the use of insecticides? ( ) Yes
( ) No
3) If yes, do you think it is effective? ( ) Yes ( ) No
4) Are you aware of the availability of resistant varieties?
( ) Yes ( ) No
5) Have you experienced breakdown of resistance of your varieties to tungro disease?
( ) Yes ( ) No
E. Awareness of mixed variety planting
1) Are you aware of mixed planting of resistant and susceptible varieties for tungro
control? ( ) Yes ( ) No
2) If yes, do you think it could control tungro disease?
( ) Yes ( ) No
3) If yes, have you tried using mixed variety to control tungro in your rice farm? ( )
Yes ( ) No
4) How long have you practiced this control method in your rice field?
125

( ) 1 season ( ) 2 seasons ( ) 3 seasons ( ) 4 seasons ( ) more
5) Have you observed the effect of mixed variety control method against tungro disease
( ) Yes ( ) No
6) Would you recommend this method to other farmers?
( ) Yes ( ) No
7) Are you still planting mixed variety in your rice farm?
( ) Yes ( ) No
8) If no, Why did you stop using mixed seeds?
( ) No tungro incidence ( ) No observed effect ( ) Too laborious
9) If no, why haven’t you applied this method in your farm?
( ) No access to mixed seeds
( ) Have no knowledge about this method
( ) Still doubtful of this method
( ) Others, What?________________
10) Are you planning to apply this method in the future?
( ) Yes ( ) No
11) Are you satisfied with the eating quality of the rice you planted?
( ) Yes ( ) No
12) Do you like to plant varieties with same eating quality as IR 64
( ) Yes ( ) No
126