A manual of rice seed health testing - IRRI books - International Rice ...
A manual of rice seed health testing - IRRI books - International Rice ...
A manual of rice seed health testing - IRRI books - International Rice ...
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Symptoms<br />
Glumes are discolored, and, in severe<br />
infection, the <strong>rice</strong> kernel shows<br />
black discoloration.<br />
Disease development<br />
High humidity and tropical temperatures<br />
during crop growth provide<br />
a congenial environment for<br />
Curvularia growth and the development<br />
<strong>of</strong> black kernel.<br />
Control<br />
Specific control measures are lacking<br />
for black kernel, but spraying with<br />
broad-spectrum fungicides can effectively<br />
arrest infestation over glumes<br />
and other plant parts. To treat <strong>seed</strong>s,<br />
slurry treatment with mancozeb has<br />
been found effective at 0.3% by <strong>seed</strong><br />
weight.<br />
Ephelis oryzae<br />
Pathogen: Ephelis oryzae (Sydow 1914)<br />
Teleomorph: Balansia oryzae sativae<br />
(Hashioka 1971)<br />
(Etymology: from udbatti, agarbatti, an<br />
incense stick)<br />
Disease: udbatta<br />
Detection level: infrequently detected,<br />
with low epidemic potential<br />
Where detected: infected <strong>seed</strong>s<br />
How detected: dry <strong>seed</strong> inspection, blot<br />
ter test, washing test<br />
Appearance: see Figure 14.5.<br />
Infected <strong>seed</strong>s appear discolored,<br />
abnormally small, deformed, and<br />
have whitish masses <strong>of</strong> conidia<br />
(Fig. 14.5a). Blackish perithecia can<br />
also be seen. Materials should be examined<br />
under a compound rnicroscope<br />
to ascertain the identity. The<br />
washing test can indicate presence <strong>of</strong><br />
E. oryzae if typical needle-shaped<br />
conidia are visible under a compound<br />
microscope.<br />
Conidia are hyaline, needlelike,<br />
and measure 13-35 × 1-2 nm<br />
(Fig. 14.5b). The perithecial stage<br />
(Hashioka 1971) consists <strong>of</strong><br />
perithecia embedded in stroma.<br />
Perithecia are ovate to pyriform and<br />
measure 125-200 × 85-100 nm. Asci<br />
are cylindrical, hyaline, eightspored,<br />
and measure 92-100 × 6 nm.<br />
Ascospores are filiform, straight or<br />
curved, 12-27 × 1 nm (CAB 1979).<br />
THE DISEASE—UDBATTA<br />
In India, udbatta occurs in Bihar,<br />
Orissa, Maharashtra, and Karnataka<br />
states, on low hills where high soil<br />
temperature (28 °C) and high soil<br />
moisture prevail (Ou 1985); Udbatta<br />
has been reported in Southwest<br />
China (Tai and Siang 1948),<br />
Hongkong, New Caledonia, and<br />
West Africa. Udbatta is internally<br />
<strong>seed</strong>borne.<br />
Symptoms<br />
Infected panicles (Fig. 14.5c,d)<br />
emerge from their sheaths as grayish<br />
white cyclindrical rods with black<br />
dots (conidial acervuli). Plants are<br />
stunted. Before panicle emergence,<br />
conidia and white mycelia form narrow<br />
stripes over the flag leaf. Systemic<br />
infection appears in all tillers<br />
<strong>of</strong> an infected plant.<br />
14.5a. Healthy<br />
<strong>seed</strong>s (L) and<br />
<strong>seed</strong>s infected<br />
with udbatta (R).<br />
b. E. oryzae<br />
conidia.<br />
c, d. Udbattainfected<br />
panicles.<br />
Disease development<br />
Mohanty (1964) report that hilly upland<br />
areas are prone to udbatta.<br />
Udbatta recurs through fungi surviving<br />
on diseased <strong>seed</strong>s. Other<br />
grass hosts may assist the spread.<br />
Udbatta may occur in cycles.<br />
Mohanty (1976) noted that high<br />
soil temperature (28 °C) and high soil<br />
moisture favor the development <strong>of</strong><br />
udbatta.<br />
Control<br />
Hot water treatment at 54 °C for<br />
10 min effectively controls udbatta<br />
(Mohanty 1975).<br />
Fungal pathogens 79