Control of Zucchini Yellow Mosaic Virus in Squash by Cross Protection. H. Lecoq, Directeurs de Recherches, INRA, Station de Pathologie Végétale, B.P. 94, 84140 Montfavet, France. J. M. Lemaire, and C. Wipf-Scheibel. Directeurs de Recherches, and Adjoint Technique, INRA, Station de Pathologie Végétale, B.P. 94, 84140 Montfavet, France. Plant Dis. 75:208-211. Accepted for publication 18 July 1990. Copyright 1991 The American Phytopathological Society. DOI: 10.1094/PD-75-0208.

A variant of zucchini yellow mosaic virus ZYMV (ZYMV-WK) that induced mild foliar mottle but no fruit symptoms on cucurbits was selected from a poorly aphid-transmissible isolate that induced severe symptoms. This mild variant could not be differentiated from its originating isolate serologically, by its host range, or by aphid transmissibility. ZYMV-WK reduced the marketable fruit production of zucchini squash only slightly when plants were infected at the seedling stage. In field trials conducted in France in 1988 and 1989, ZYMV-WK proved to be very efficient in protecting two cultivars of zucchini squash from severe ZYMV under intense disease pressure. Increase in weight of marketable fruit in cross-protected plots was up to 14.7 times that in unprotected plots.