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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For further details, see the Commonwealth<br />
Institute <strong>of</strong><br />
Helminthology Description <strong>of</strong> plant<br />
parasitic nematodes, Set 1, No. 4 by<br />
Franklin and Siddiqi (1972).<br />
THE DISEASE—WHITE TIP<br />
The disease is known in most <strong>of</strong> the<br />
world's <strong>rice</strong>-growing areas. Yield<br />
loss depends on infestation level and<br />
other factors such as climate, variety,<br />
and agronomic practices (Bridge et<br />
al 1990).<br />
Symptoms<br />
Leaf tips first turn white, from the<br />
tip and extending downward 3-5 cm.<br />
Infected plants lose vigor and are<br />
stunted. The flag leaf twists, affecting<br />
panicle emergence. Small panicles<br />
are partially exserted, the uppermost<br />
part remains sterile and lacks<br />
spikelets (Fig. 16.2). In severely infected<br />
plants, panicles are affected.<br />
Infected grains are sometimes distorted.<br />
Yoshii and Yamamoto (1950)<br />
note that not all infected plants or<br />
tillers exhibit symptoms. Tolerant<br />
varieties are sometimes asymptomatic<br />
while harboring the pests.<br />
In white tip caused by insect damage,<br />
leaves also show perforations.<br />
16.2 White tip disease<br />
<strong>of</strong> <strong>rice</strong> caused<br />
by A. besseyi.<br />
Disease development<br />
Both upland and lowland environments<br />
support the disease.<br />
The nematode survives in glumes<br />
from 8 to 36 mo, depending on storage<br />
conditions. A. besseyi feeds<br />
ectoparasitically on leaf apical<br />
meristems. It proliferates and enters<br />
the spikelets before anthesis and<br />
feeds on ovaries, stamens, and embryos.<br />
As the grain matures, nematodes<br />
stop multiplying and coil in<br />
the glume.<br />
Infestation rarely occurs through<br />
the soil, commonly through infested<br />
<strong>seed</strong>s and diseased husks. The<br />
nematode is disseminated through<br />
irrigation water. Infestation and disease<br />
development are facilitated by<br />
flooded soil, high temperature, and<br />
nitrogenous manures.<br />
Control<br />
Seeds may be treated with<br />
nematicide or hot water (52-57 °C for<br />
15 min).<br />
98 <strong>Rice</strong> <strong>seed</strong> <strong>health</strong> <strong>testing</strong> <strong>manual</strong>