Protein Coats of Two Strains of Cucumber Mosaic Virus Affect Transmission byAphis gossypii

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Abstract
Strains (2) of cucumber mosaic virus (CMV) were studied to determine the reasons for differences in transmission efficiency by A. gossypii. Strain CMV-T, which is highly transmissible from tobacco to cucumber (90%) and CMV-6, a poorly transmitted one (10%) were used. Difference in transmission was independent of host plant and was not correlated with concentration of virus in the leaf. There were no indications of a helper factor associated with CMV-T or of an inhibitor that decreased transmission of CMV-6. Purified CMV-6 at high concentrations was acquired through a parafilm membrane almost as efficiently as was purified CMV-T, and subsequently was transmitted by aphids to test plants. Reducing virus concentration decreased transmission of CMV-6 markedly; that of CMV-T was decreased much less. Differences in RNA profiles were observed after electrophoresis in acrylamide gels. Exchanging CMV-6 coat protein with CMV-T coat in vitro increased aphid transmission rates markedly, whereas replacing CMV-T coat by CMV-6 protein decreased transmission. Results were supported by enzyme-linked immunosorbent assay of single aphids. The coat protein determines transmissibility of CMV strains by aphids.