Resistance in Germplasm of Cucurbita Pepo to Silverleaf, a Disorder Associated with Bemisia argentifolii (Homoptera: Aleyrodidae)

Abstract

Elite breeding lines and susceptible varieties of Cucurbita pepo L. (zucchini and yellow crookneck squash) and accessions of two wild species, Cucurbita ecuadorensis Cutler and Whitaker and Cucurbita martinezii Bailey, were evaluated in spring and fall 1995 for resistance to silverleaf whitefly, Bemisia argentifolii Bellows & Perring, and to squash silverleaf, a physiological disorder associated with feeding by B. argentifolii. Populations of whitefly and severity of silvering were greater in the spring season than in the fall. In general, the yellow squash variety, ‘Supersett’, and the two yellow squash breeding lines (A24-10 and K26-4) supported larger populations of whitefly than the zucchini variety, ‘Elite’, and A21-7 and Sunseeds 3, the zucchini breeding lines. However, whitefly populations within the yellow squash cultigens or within the zucchini cultigens did not differ significantly. In contrast, ‘Elite’ was severely silvered in the spring (average rating of 4.8 at the end of the season) while Sunseeds 3 never exhibited silverleaf and only one plant of A21-7 exhibited slight silvering (rating of 1). ‘Supersett’ was usually significantly more silvered than the yellow squash breeding lines, but the lines nevertheless exhibited significant 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 two wild species, C. ecuadorensis and C. martinezii, all supported moderate populations of whiteflies and developed silverleaf. In the case of the zucchini breeding lines, silverleaf severity was not related to numbers of immature whiteflies. Resistance to silverleaf in the zucchini breeding lines may be due to some form of tolerance to the effects of whitefly feeding.