Rapid Induction and Severity of Symptoms in Zucchini Squash (Cucurbita pepo) Map to RNA 1 of Cucumber Mosaic Virus. Marilyn J. Roossinck. Department of Plant Pathology, Cornell University, Ithaca, NY 14853 U.S.A. Peter Palukaitis. Department of Plant Pathology, Cornell University, Ithaca, NY 14853 U.S.A. MPMI 3:188-192. Accepted 10 January 1990. Copyright 1990 The American Phytopathological Society.

Two strains of cucumber mosaic virus (cucumovirus group), Fny-CMV and Sny-CMV, were used to genetically map phenotypic differences in severity and timing of symptoms in zucchini squash. Pseudorecombinants were constructed between the two strains, and the genetic purity of the pseudorecombinant strains was verified by molecular heterogeneity analysis of the viral RNAs using an RNase protection assay. Assessment of symptoms induced by the pseudorecombinant strains indicated that RNA 1 is responsible for both the severity and the rapid induction of symptoms elicited by Fny-CMV in zucchini squash. The potential role of RNA 1 in the induction of pathogenicity is discussed.