Diamondback moth (Lepidoptera: Plutellidae) resistance of Brassica napus and B. oleracea lines with differing leaf characteristics.

Canola quality oil produced from oilseed rape, Brassica napus L. (Brassicaceae), is a relatively new crop in the United States and is damaged by a number of insect pests, including the crucifer specialist diamondback moth, Plutella xylostella (L.). Greenhouse tests were performed to evaluate resistance in normal-leafed ('Bingo', 'Cobra', 'Oscar') and glossy-leafed B. napus plants ('glossy Bingo' and plant introductions (PI) 469895, 470055, 470055-2, and 470064) to identify potential resistant sources to diamondback moth. Normal-leafed PI 171538, originally described as B. napus and recently reclassified as B. oleracea, also was evaluated for resistance with B. napus plants and B. oleracea cultivars of broccoli, 'Green Comet', 'Green Valiant', and collard 'Vates'. Plants of Cornell line 92-8611, a broccoli with glossy-leaf type (glossy broccoli), were used as the resistant control in all trials. B. napus entries failed to show feeding nonpreference or antibiosis comparable to that of glossy broccoli, Furthermore, no significant differences were detected between normal and glossy-leafed B. napus lines for most of the parameters tested. Within the tested B. napus entries, PI 470055 exhibited low levels of feeding damage in the restricted-feeding test and some level of antibiosis against diamondback moth. However, B. oleracea entry PI 171538 showed a greater or comparable level of resistance to that of glossy broccoli. Nonpreference for larval feeding and adult oviposition were exhibited by PI 171538. In feeding tests, PI 171538 was less defoliated compared with other B. oleracea entries. Diamondback moth larvae reared on PI 171538 leaves for 5 d had a lower head capsule width compared with larvae reared on other entries. In an oviposition preference test, PI 171538 received 0.9% of eggs as compared with normal-leafed B. napus plants (2.1-4.4%) and glossy broccoli, which received 7.0% of eggs. The experiments indicate that the normal-leafed B. oleracea entry PI 171538 has considerable resistance against diamondback moth. PI171538 is a newly discovered source of resistance and has leaf characteristics that differ from the previously reported diamondback moth-resistant B. oleracea lines.