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

Table 10.2. continued
Disease
Growth stage at which
inspection is made a
Scale (degree of severity)
Rice tungro (RTV)
Rice ragged stunt (RSV)
See note in RTV.
Grassy stunt (GSV)
Note: Scale being developed.
2
(greenhouse)
3-5
(field)
2-3
(greenhouse)
4-6 (field)
2-3
(greenhouse)
3-6
(field)
Scale (based on symptom severity
3 wk after inoculation)
1 No symptoms
3 1-10% plant height reduction,
no distinct leaf discoloration
5 11-30% height reduction; no
distinct leaf discoloration
7 31-50% height reduction and/or
yellow to orange leaf discoloration
9 More than 50% height reduction;
and yellow to orange leaf
discoloration
Scale (based on symptom severity
5 wk after inoculation)
1 No symptoms
3 0-10% plant height reduction; no
short, ragged, or curled leaves
5 0-10% height reduction; youngest
normal leaves, 1-2 older leaves
abnormal
7 10-30% height reduction; with
youngest normal leaves; may
have 3-4 abnormal older leaves
9 More than 30% height reduction;
or with abnormal leaves including
the youngest
General scale can be used in the
meantime
0 No infection
1 1-10%
3 11-30%
5 31-70%
7 51-70%
9 71-100%
Sheath blight (ShB)
Pathogen: Thanatephorus cucumeris
( Rhizocotonia solani )
Sheath rot (ShR)
Pathogen: Sarocladium oryzae
7-8
7-9
Scale (based on relative lesion
height)
0 No infection observed
1 Lesions limited to lower 20% of
the plant height
3 20-30%
5 31-45%
7 46-65%
9 More than 65%
Scale (incidence of severely affected
tillers)
0 No incidence
1 Less than 1%
3 1-5%
5 6-25%
7 26-50%
9 51-100%
Field inspection 55