Abstract
The rice stem nematode Ditylenchus angustus(Butler, 1913) Filipjev,
1936., was successfully cultured on Rhizoctonia solani Kuhn. growing on
autoclaved rice grains, but failed to grow on excised pieces of rice stems, leafsheaths, boots, carrot slices, and potato slices. The growth of nematode was
poor on the other six fungi used for its cultivation. The cultured nematodes were
similar to the nematodes isolated from ufra infected rice plants in terms of
morphology and infectivity to rice plants. Its life cycle from egg to egg was
completed in 11-15 days in rice plants and 11-17 days in fungal culture. The five
growth stages of the nematode are described. Based on direct observations on
the molting larvae, the body length ranges of the three larval groups were
determined.
The nematode is amphimictic, failing to reproduce parthenogenetically on
rice plants. In a glasshouse pot experiment, the number of generations was six
in transplanted Aman and eight on deepwater Aman rice. The nematode
survived 14-22 days in water at the ambient temperature, but more than 40 days
in cold water at 6°C. In water, the lethal high temperature for the nematode was
43° for six hours, while it survived only 30 minutes at chilling temperature.
Higher concentrations of sodium chloride (1.20%) was toxic to the nematode in
vitro, but rice plants grown in 0.5% saline soil (ECe 11.6 ds/m) were susceptible
to the disease.
The nematode entered rice grains but did not survive more than a month
in dried seeds with moisture content below 14%. Rice field straw and stubble
were the most potential sources of nematode survival. Low temperature (6°C)
and moist condition prolonged cryptobiotic survival of the nematodes in rice
straw compared to higher temperature (30°C) and continuous dry condition.
Forty percent of rice stubble in the field harboured viable nematodes even five
months after harvest. Nematode survival in dry or moist soil was found unlikely.