Seed Transmission of Lettuce Mosaic Virus in Mosaic Resistant Lettuce1

Mosaic-susceptible and -resistant lettuce cultivars and breeding lines were evaluated for seed transmission of the virus. Two methods of indexing were used: the seedling method, in which seedlings from infected plants were observed; and the Chenopodium method, in which a local lesion host, C. quinoa, was inoculated with seed samples ground in buffer solution. Susceptible lines transmitted at a rate averaging about 2% per plant. Over 90% of resistant lines failed to transmit the virus; the rest transmitted at extremely low rates, averaging 0.49% in one experiment. The parent plant’s environment appears to affect the transmission rate. Low day temperature results in a higher rate than high.