Sorghum Diseases in India

lines) and tar spot (51 resistant lines). Not one of
the lines or varieties was completely free of gray
leaf spot or tar spot, but expression of symptoms
is delayed in resistant plants and fewer lesions
appear. However, when 88 sorghum lines were
inoculated with Rhizoctonia solani all of the lines
were susceptible. Similarly, 50 lines tested for
resistance to head molds showed infection (Dalmacio
et al. 1981, Dalmacio 1982). Sources of resistance
to most of the important sorghum
diseases have been identified.
Furthermore, Paderes and Dalmacio (1984)
examined resistance to tar spot by evaluating
components of rate-reducing resistance to Phyllachora
sorghi (Syn P. sacchari). The findings reveal
that resistance prolonged the latent period
(LP) by 12%, shortened the infectious period (IP)
by 69%, reduced stomata size (SS) by 85%, and
reduced sporulation capacity (SC) by 93%.
Among these components, IP, SS, SC, and infection
frequency (IF) may be considered more
important than LP. Correlation analysis showed
that LP, SS, and SC were more strongly associated
with each other than with IP.
Screening work of 120 sorghum genotypes of
the International Sorghum Multiple Disease Resistance
Nursery (ISMDRN) established at the
Southern Mindanao Agricultural Research Center
(SMARC) showed mean severity ratings
ranging from 1.3 for zonate leaf spot and Rhizoctonia
disease to 4.5 for grain molds. (Table 3).
Table 3. Disease reactions of 120 ISMDRN'87
sorghum entries screened at SMARC-USM,
Tangonan, Kabacan, Cotabato, the Philippines,
1987.
Mean severity
Disease ratings 1
Zonate leaf spot 1.3
Gray leaf spot 1.9
Target leaf spot 1.7
Rhizoctonia banded leaf
and sheath blight 1.3
Anthracnose 1.5
Tar spot 3.5
Grain mold 4.5
Root/stalk rots 1.8
1. Scored on a 1-5 scale, where 1 = no symptoms and
5 = severe infection.
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Phyllachora tar spot and head/grain mold
were severe and sorghum hybrids and cultivars
tested were susceptible to these two diseases.
Other foliar diseases had ratings ranging from
1.3 to 1.9, and the sorghum genotypes were
resistant to most foliar diseases except tar spot.
Head/grain mold infection had a mean severity
of 4.5 (Table 3).
The incidence of a stalk rot complex in sorghum
fields at SMARC-USM was also observed
to be infecting most hybrids and cultivars tested.
It was believed to have been caused by the combined
effect of Colletotrichum graminicola, Fusarium
moniliforme, and Rhizoctonia solani
An interesting development was the release
of a new sorghum hybrid by Pioneer Overseas
Corporation, Philippines. This hybrid, Pioneer
8258, was noted to have excellent resistance to
target and gray leaf spots and some degree of
resistance to Rhizoctonia disease, although Rhizoctonia
resistance seems to be highly influenced
by plant height.
Research Needs
During the First National Symposium and Workshop
on Corn and Sorghum Crop Protection,
held at the University of Southern Mindanao,
17-20 Mar 1982 [sponsored by the Philippine
Council for Agriculture and Resources Research
and Development (PCARRD) and the Ministry
of Agriculture and Food (now the Department
of Agriculture)], Dalmacio and Exconde listed
the Philippine research needs in sorghum pathology,
as follows:
1. Monitor disease occurrence on sorghum sowings
during the dry season and determine the
relative importance.
2. Search for sources of resistance to various diseases
and develop resistant varieties.
3. Establish disease nurseries in various sorghum-growing
areas.
While yield loss has been demonstrated in
field experiments, it is necessary to determine
the precise yield losses in cultivars and hybrids,
at different disease intensities, during each cropping
or sowing season (Exconde 1982).
Table 4 summarizes the research areas and
current status of sorghum disease management
for 13 sorghum diseases in the Philippines.
Much remains to be studied in the areas of yieldloss
assessment, epidemiology, host-pathogen