Resistance and Susceptibility to Insect Pests in Glossy Genetic Lines of Brassica oleracea in Connecticut, USA

The glossy cauliflower PI 234599 has been used in breeding programs as a source of resistance to diamondback moth, Plutella xylostella (L.), and other lepidopterous larvae, but the relationship between insect resistance and glossiness has not been clear. One way to clarify this relationship is to find glossy lines carrying different genes for glossiness and test their resistance to insects. In the process, additional sources of resistance may be identified. Ten glossy lines of broccoli, cauliflower, kale, and collards with at least four different genes for glossiness (three recessive nonallelic genes and at least one dominant gene) were tested in the field under natural infestation for resistance. The insect species studied were imported cabbageworm (Pieris rapae (L.)), diamondback moth (Plutella xylostella (L.)), cabbage aphid (Brevicoryne brassicae (L.)), and flea beetles (mainly Phyllotreta cruciferae (Goeze), but also Phyllotreta striolata (F.)). Al l glossy lines were resistant to cabbage aphid and all except one was consistently resistant to imported cabbageworm. They were susceptible to flea beetles, although less susceptible in the fall than in spring. Their resistance to diamondback moth varied greatly among plantings, probably because of the low insect population in Connecticut. In order for these additional glossy lines to become useful sources of resistance to diamondback moth, they need to be tested and bred where this insect is a serious problem, instead of under low natural populations or artificial infestations in the northeastern USA.