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