A manual of rice seed health testing - IRRI books - International Rice ...

Plant growth stages, number
of field inspections, and
counts per inspection
Crop health inspections must he
timed with specific plant growth
stages. Schedule observations to allow
verification of the incidence of
various diseases when they appear
at specific plant parts (such as the
leaf, leaf sheaths, neck, panicle, and
spikelets). For production of foundation
and certified rice seed, a minimum
of two inspections are required
from flowering to harvest stages
(Svensson et al 1975). Make 5 counts
per inspection if the field is not
larger than 2 ha. Increase counts by
one for each additional 2 ha or part
thereof. Inspect 1000 plants or heads
per count (Anonymous 1972).
Field count methods
For field counts and seed certification,
more plots and number of
plants or heads are counted than for
quarantine inspections. Procedures
are devised to randomly check the
specified number of heads or plants
at different field sites. For seed certification,
the methods outlined by
Agarwal (1980) are useful when inspecting
large areas and many
plants.
For quarantine purposes, the
fields or number of plants to be observed
are small, and the inspector
can check every plant. For example,
in germplasm exchange, a small
number of seeds are multiplied in
glasshouses or in open quarantined
fields, and all are examined very
carefully.
Table 10.1. Growth stages of the rice plant and their respective codes.
Code
1
2
3
4
5
6
7
8
9
Stage
Table 10.2. Disease, stage of inspection, and scale of symptoms.
Disease
Fungi
Leaf blast (BI)
Pathogen: Magnaporthe grisea
( Pyricularia oryzae – imperfect
or anamorph stage)
Growth stage at which
inspection is made a
2-3
Germination
Seedling
Tillering
Stem elongation
Booting
Heading
Milk stage
Dough stage
Mature grain
Scale (degree of severity)
Scale (for blast nursery)
(Note: scale 1-4 is qualitative,
5-9 is quantitaitve).
0 No lesions
1 Small brown pinpoint-size specks,
or larger brown specks without
sporulating center
2 Small roundish to slightly
elongated, necrotic gray spots,
approximately 1-2 mm in diam,
with distinct brown margin;
lesions mostly found on the
lower leaves
3 Lesion type as in scale 2, but a
significant number of lesions
are on the upper leaves
4 Typical susceptible blast lesions
as in types 5, 7, and 9 below,
3 mm or longer, infecting less
than 2% of the leaf area. Lesion
type 3 mm or longer is the qualitative
type for susceptible blast
lesions. Increasing amount of
these lesions on leaves will
classify reaction into scales 5-9.
5 Typical blast lesions infect
2.10% of the leaf area
6 Typical blast lesions infect
11-25% of the leaf area
7 Typical blast lesions infect
26-50% of the leaf area
8 Typical blast lesions Infect
51.75% of the leaf area; many
dead leaves
9 More than 75% leaf area affected
2-3
(field or
greenhouse)
Scale (predominant lesion type)
0 No lesions
1 Small brown pinpoint-size specks,
or larger brown specks without
sporulating center
3 Small, roundish to slightly
elongated necrotic sporulating
spots, approximately 1-2 mm
diarn with a distinct brown margin
or yellow halo
52 Rice seed health testing manual