Characteristics of Glossy Leaf Waxes Associated with Resistance to Diamondback Moth (Lepidoptera: Plutellidae) in Brassica oleracea

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Abstract
Larval survival and mining damage by Plutella xylostella (L.) were significantly lesson 10glossy-leaf Brassica oleracea L. genotypes with different genetic backgrounds than on eight controls with normal waxy bloom. Leaf surface wax crystallite density and total amount of leaf wax explained 69% of the variation in larval survival on the genotypes, based on linear regression analysis. The glossy genotypes also differed in chemistry and morphology of leaf surface waxes, which may account for additional variation in larval survival. Leaf mining by first instars was highly correlated with survival to fourth instar on glossy lines but not on normal lines. Neonate larvae also moved significantly faster on glossy resistant plants. The findings are consistent with a hypothesis that neonates reject glossy plants and fail to establish on them, leading to the observed resistance. This hypothesis, formerly proposed to explain resistance in glossytypes descended from cauliflower PI 234599, may now be extended to include glossy types from other genetic sources. The data indicate that glossyleaf wax characteristics, regardlessof genetic source, confer some level of resistance to P. xylostella. The data also suggest that incorporation of genes that cause the greatest reduction in amount of leaf wax and crystallite density will permit development of the most resistant cultivars.

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