Resistance to Diamondback Moth in Brassica: Mechanisms and Potential for Resistant Cultivars

Resistance to diamondback moth, Plutella xylostella (L.), has been a major criterion for selection in the crucifer breeding program at the New York State Agricultural Experiment Station. Two types of resistance have been identified and studied. Larval survival on normal wax genotypes (with the typical whitish bloom of cultivated Brassica) is about 50% of survival on susceptibles. Polar extracts of the resistant plants reduce larval survival when added to an artificial diet, but the active compounds have not yet been identified. Larval survival on glossy wax genotypes (lacking the normal bloom) is reduced to as low as 1%, compared with standard cultivars. Glossy resistance is associated with reduced wax and reduced density of wax crystalline structures (crystallites) on leaf surfaces. Leaf wax load and crystallite density explain 69% of the variation in survival on a collection of 18 glossy and normal bloom genotypes of Brassica oleracea, based on regression analysis. Glossy leaf waxes apparently elicit nonacceptance behaviors in neonate larvae which result in their failure to successfully establish on these plants. Knowledge of resistance mechanisms will facilitate the development of B. oleracea cultivars resistant to diamondback moth.