Bell pepper plants showing vein yellowing and leaf roll symptoms were observed in plastic houses at Kitanakagusuku, Okinawa Prefecture in 1981. The causal agent did not infect plants by mechanical inoculation or through seed but was transmitted by grafting and two species of aphids, Aphis gossypii Glover. collected from pepper and Myzus persicae Sulz. in a persistent manner. The causal agent has limited host range, only infect Capsicum species. In serological tests this agent did not react with antisera to potato leaf roll virus, tobacco necrotic dwarf virus, barley yellow dwarf virus and beet western yellows virus. Partially purified preparations contained spherical particles 25nm in diameter. In ultrathin sections virus-like particles were observed only in the phloem cells of infected pepper plants. Based on these results the causal agent was classified as a new member of the luteovirus group and named pepper vein yellows virus (PeVYV).
Systemic infection of cucumber mosaic virus (CMV) in Cucumis figarei at high temperature was investigated using reassortants and chimeric RNAs. Three CMV strains of pepo-, SO-, MY17-and Y-CMV were used: pepo-, SO-and MY17-CMV systemically infected C. figarei at 36•Ž, whereas Y-CMV did not as previously described. Inoculation with in vitro transcripts from biologically active cDNA clones of Y-CMV and pepo-CMV RNAs 1, 2 and 3 indicated that only the inocula containing pepo-CMV RNA3 induced systemic infection at 36•Ž, suggesting that the resistance against systemic infection by Y-CMV and its breakage by pepo-CMV were mapped to CMV RNA3. Inoculation with transcripts from the cDNA clones of Y-CMV RNAs 1, 2 and RNA3 of SO-CMV or MY17-CMV provoked systemic infection at high temperature, indicating that the systemic infection by SO-CMV or MY17-CMV was also mapped to RNA3. Analysis with chimeras constructed between cDNA clones of Y-CMV and pepo-CMV RNA 3 showed that the resistance and resistance breakage were mapped to the coat protein gene on CMV RNA3. Comparison of the nucleotide sequence of pepo-, SO-and MY17-CMV RNA3 with that of Y-CMV RNA3 revealed that the coat protein of Y-CMV differs from those of pepo-, SO-and MY17-CMV in four amino acids at positions 17 (Leu to Pro), 25 (Ser to Pro), 28 (Ser to Ala) and 129 (Ser to Pro). These results suggested that all or some of the four amino acids play an important role in determining long-distance movement of CMV in C. figarei at a high temperature.
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