The S RNA segment determines symptom differences on Tetragonia expansa between two Watermelon silver mottle virus isolates

摘要

The WS-Y isolate of Watermelon silver mottle virus (WSMoV) causes severe necrosis in Tetragonia expansa. To determine the RNA segment that induces symptoms, genome reassorants between WS-Y and an isolate causing mild mottle, WS-O, were generated. The origin of each segment in the reassortants was identified by RT-PCR and subsequent restriction enzyme analysis of the amplified fragments. Thirty genome reassortants were isolated from co-infected T. expansa plants. The reassortants with the S RNA segment of WS-Y caused severe necrosis, while those with the S RNA segment of WS-O caused a mild mottle; hence, the S RNA determined symptom expression. The incidence of reassortants was disproportional among genotypes. The most frequent genome reassortant possesses the L RNA of WS-Y, the M RNA of WS-O and the S RNA of WS-Y. A similar ratio of genotypes was found in isolates of local lesions on Chenopodium, quinoa. These results strongly suggested that competition occurred independently between the individual RNA segments in a co-infected T. expansa plant, not between isolates.