Resistance of rape (Brassica napus) to attack by the cabbage aphid (Brevicoryne brassicae L.)

Resistance to Brevicoryne brassicae L. attacks in a New Zealand variety of forage rape resulted from a combination of host non–preference and antibiosis. Using clonal plant material obtained from cuttings, only half the numbers of immigrant alate cabbage aphids that settled to reproduce on the susceptible rape were to be found on the resistant rape. The reproduction rate of these alates was about 12 % slower on the resistant plants than on the susceptibles and the young took about 13% longer to mature. Antibiosis then shortened the reproductive life of the apterae by one-third, reduced their fecundity by nearly 50 % and caused 40% mortality in their progeny. The over-all effect of this was considerable and under conditions specified in the text could result in the population on the resistant plants being about one-eighth that on the susceptible plants in under 1 month. The resistant plants lost their resistance on flowering and became normally susceptible to cabbage aphid attack. With maturity, however, the B. brassicae-resistant plants became slightly resistant to Myzus persicae.