RESISTANCE IN GERMPLASM OF CUCURBITA-PEPO TO SILVERLEAF, A DISORDER ASSOCIATED WITH BEMISIA-ARGENTIFOLII (HOMOPTERA, ALEYRODIDAE)

Elite breeding lines and susceptible varieties of Cucurbita pepo L. (z ucchini and yellow crookneck squash) and accessions of two wild specie s, Cucurbita ecuadorensis Cutler and Whitaker and Cucurbita martinezii Bailey, were evaluated in spring and fall 1995 for resistance to silv erleaf whitefly, Bemisia argentifolii Bellows & Perring, and to squash silverleaf; a physiological disorder associated with feeding by B. ar gentifolii. Populations of whitefly and severity of silvering were gre ater in the spring season than in the fall. In general, the yellow squ ash variety, 'Supersett', and the two yellow squash breeding Lines (A2 4-10 and K26-4) supported larger populations of whitefly than the zucc hini variety, 'Elite', and A21-7 and Sunseeds 3, the zucchini breeding lines. However, whitefly populations within the yellow squash cultige ns or within the zucchini cultigens did not differ significantly. In c ontrast, 'Elite' was severely silvered in the spring (average rating o f 4.8 at the end of the season) while Sunseeds 3 never exhibited silve rleaf and only one plant of A21-7 exhibited slight silvering (rating o f 1). 'Supersett' was usually significantly more silvered than the yel low squash breeding lines, but the lines nevertheless exhibited signif icant levels of silvering (average rating of 3.2 compared to 3.9 for ' Supersett' at the end of the spring season). Four accessions of the tw o wild species, C. ecuadorensis and C. martinezii, all supported moder ate populations of whiteflies and developed silverleaf. In the case of the zucchini breeding lines, silverleaf severity was not related to n umbers of immature whiteflies. Resistance to silverleaf in the zucchin i breeding lines may be due to some Form of tolerance to the effects o f whitefly feeding.