Characterization and ecological aspects of rice yellow mottle virus in Kenya

Rice yellow mottle virus(RYMV)is the causal pathogen of yellow mottle of rice in the area around Kisumu near Lake Victoria in Kenya. Affected plants show a yellow or orange discolouration of the leaves, reduced tillering and stunting of the plants, and sterility of the flowers. The results of this study gave the following cryptogram forRYMVR/1:1.4/23:S/S:S/Cl.RYMVis easily mechanically transmissible. Experimentally a limited number of plants belonging to the family Gramineae only were found to be a host for the virus. Rice was the only host found naturally infected withRYMV.Beetles belonging to the subfamilies Criocerinae, Cryptocephalinae, Galerucinae, Halticinae and Hispinae of the family Chrysomelidae, and the long-homed grasshopper Conocephalus merumontanus Sjöstedt (Tettigoniidae) also transmitted the virus. Chaetocnema pulla Chapuis (Halticinae) proved to carry the virus in the field.RYMVis a stable virus with a particle diameter of about 25 nm and sediments as a single component. The base composition of theRNAis similar, but not identical to that of cocksfoot mottle virus. Serologically no relationship nor any other affinity was established betweenRYMVand a number of other isometric plant viruses of comparable size.Infected rice is considered to be the main source of the virus in the rice fields. Control of the disease must be sought in cultivation practices and growing of rice with short vegetative periods. Breeding of rice varieties for resistance toRYMVhas to be initiated.