Abstract
Studies on the mechanism of resistance of some Rayada (Deepwater rice grown in
deepwater rice fields in Faridpur) and non-Rayada rice entries to rice tungro disease (RTD)
revealed that the resistance of a rice variety/line to the disease is not always related to the
resistance to the vector green leafhopper (GLH). All of the test varieties including the tungro
resistant Utri Merah were susceptible to GLH in respect of nymphal survival, adult life span, and
host preference when compared with the GLH-susceptible BR3. The insects fed predominantly
from phloem tissue areas except in Habj.DW8 where feeding was chiefly restricted in Xylem.
BR1867-20-1-4, Kataribhog and Purbachi reacted as susceptible to RTD, while Utri Merah,
Habj.DW8 and the Rayadas showed resistance at all levels of disease pressure at all ages of
inoculation. Plant age at inoculation did not cause any change in the level of reaction to RTD
except at 40 DAS, where the disease incidence was comparatively low in BR1867-20-1-4 and
Kataribhog. Post inoculation effects showed that the disease (tungro) incidence, reduction in
plant height, and tungro virus recovery were consistently high in Kataribhog and Purbachi, but
much lower in Habj.DW8, Utri Merah and Rayadas. BR1867-20-1-4 possessed quick recovery
ability from RTD as the virus recovery of the inoculated plants sharply declined to zero and
consequently the symptom type shifted from destructive to prospective status, and the rate of
reduction in plant height declined over time. The susceptible varieties, Kataribhog and Purbachi,
consistently exhibited destructive symptoms, while the resistant ones initially showed
prospective symptoms that disappeared within 3-4 weeks after inoculation. Rayada entries did
not produce any destructive symptom even when the young seedlings were exposed to the
viruliferous GLH for 10 hours. They were also disease free when inoculated at maximum
be used as resistant and tillering stage in the field. Habj.DW8 and Rayadas may
BR1867-20-1-4 as a desired line in developing tungro resistant rice varieties.