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

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