| Two types of resistance to Plutella xylostella L. were found in cabbage breeding lines in Dr. M. H. Dickson's program at the New York State Agricultural Experiment Station at Geneva, New York.; Resistance in normal wax genotypes (displaying the whitish bloom typical of cultivated Brassica) was shown, by artificially infesting plants, to result from reduced larval survival. Polar extracts of these plants reduced larval survival when added to an artificial diet, but the active compounds could not be isolated. It was hypothesized that a combination of chemical factors present in foliage caused reduced survival of P. xylostella on resistant normal wax genotypes.; Resistance in glossy wax genotypes (lacking the normal bloom) was shown to result from greatly reduced survival of newly hatched P. xylostella larvae, but extracts from resistant glossy plants were inactive in diet. Methods were devised, employing video and microcomputer technology, to conduct quantitative studies of neonate behaviors on plants. The insects were found to move faster and spend more time walking and searching, and less time feeding, on glossy resistant plants than on susceptibles.; Study of neonate behavior on leaves with waxes removed or mechanically altered, and on isolated leaf waxes, confirmed that the larval nonpreference behaviors occurred in response to leaf waxes of resistant glossy plants. Specifically, reduced amounts of wax and reduced densities of wax crystallites on leaf surfaces elicited nonpreference. Studies with isolated waxes suggested that wax chemistry might also be involved.; A collection of genetically diverse glossy Brassica oleracea genotypes all reduced P. xylostella survival. However, effectiveness varied among seven tentatively identified genes producing the glossy trait in this collection. Two of these genes were identified as most promising. By using these superior genes and selecting for further reduction in amount of leaf wax and crystallite density, high levels of resistance to P. xylostella can potentially be developed and maintained.; Other studies addressed the effects of plant age and environmental conditions on expression of resistance to P. xylostella in Brassica oleracea.; This research will facilitate development and deployment of crops resistant to P. xylostella, which is among the world's most serious agricultural pests. |
