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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Kernel smut is <strong>seed</strong>-transmitted.<br />
It may reduce grain quality if incidence<br />
is high. Most <strong>rice</strong>-importing<br />
countries exclude <strong>seed</strong>s infected<br />
with kernel smut or demand that<br />
<strong>seed</strong>s be properly treated before<br />
shipment.<br />
Symptoms<br />
The disease can be detected in the<br />
field only at panicle maturity.<br />
Minute carbon black pustules or dots<br />
can be seen on the glumes. In severe<br />
infections, rupturing glumes show<br />
beaklike outgrowths (Fig. 14.12e).<br />
When smut balls burst, spores lodge<br />
on <strong>health</strong>y spikelets and leaves. The<br />
black spores can be seen in the field.<br />
Disease development<br />
Kernel smut develops more <strong>of</strong>ten<br />
and more severely in lowland than<br />
in upland ecosystems.<br />
Chlamydospores persist for more<br />
than 3 yr. At germination, they produce<br />
many sporidia which in turn<br />
may produce secondary sporidia.<br />
Secondary sporidia are sickle-shaped<br />
and are forcibly discharged. They<br />
can infect <strong>health</strong>y florets. Infected<br />
florets may be fully or partially<br />
smutted.<br />
Heavy application <strong>of</strong> nitrogenous<br />
fertilizers and the use <strong>of</strong> late-maturing<br />
varieties increase the incidence<br />
<strong>of</strong> kernel smut.<br />
High humidity and high temperature<br />
(25-30 °C) at anthesis favor disease<br />
development.<br />
Control<br />
Seed treatment with fungicides, hot<br />
water, or both is applied to infected<br />
<strong>seed</strong>s as a precautionary quarantine<br />
measure prior to shipment.<br />
Ustilaginoidea virens<br />
Pathogen: Ustilaginoidea virens (Cooke)<br />
Takahashi (Takahashi 1896)<br />
(Etymology: from Latin ustilo, to burn a<br />
little; viren, green)<br />
Disease: false smut or green smut<br />
Detection level: infrequently detected<br />
(0.1-7% <strong>of</strong> <strong>seed</strong> lots tested), with low<br />
epidemic potential<br />
Where detected: infected <strong>seed</strong>s<br />
How detected: dry <strong>seed</strong> inspection, wash<br />
ing test<br />
Appearance: see Figure 14.13.<br />
The fungus appears from within infected<br />
mature spikelets (Fig.<br />
14.13a,b). The spore ball is initially<br />
yellowish to orange, later turns olive<br />
green to dark greenish black. Fleshy<br />
inside while young, thc ball becomes<br />
hard at maturity. The central<br />
mycelial mass is hard and composed<br />
<strong>of</strong> thin, hyaline hyphae. The outer<br />
sporiferous region is three-layered.<br />
The outermost layer is greenish<br />
black with powdery spores; the middle<br />
layer, orangish; the innermost,<br />
yellowish. Spores are small, smooth<br />
to warty, olivaceous, spherical, and<br />
measure 3-5 × 4-6 nm in diameter<br />
(Fig. 14.13c).<br />
The teleomorph is not commonly<br />
encountered.<br />
THE DISEASE—FALSE SMUT OR<br />
GREEN SMUT<br />
False smut or green smut was first<br />
reported in Tirunelveli, Tamil Nadu,<br />
India, in 1878, and later in many<br />
countries (Japan, the USA, Philippines,<br />
Myanmar, Sri Lanka, China,<br />
and others).<br />
Because the disease attacks crops<br />
that are <strong>health</strong>y, many farmers believe<br />
the appearance <strong>of</strong> false smut<br />
signals a bumper harvest. Observations<br />
by Rao (1964) support the<br />
farmers' belief.<br />
14.23a. Panicle<br />
showing smutted<br />
<strong>seed</strong>s. b. Smutted<br />
<strong>seed</strong>s (L) and<br />
<strong>health</strong>y <strong>seed</strong>s (R).<br />
c. Spores <strong>of</strong> U.<br />
virens.<br />
88 <strong>Rice</strong> <strong>seed</strong> <strong>health</strong> <strong>testing</strong> <strong>manual</strong>