Abstract
Two Japonica type breeding lines of rice, Saikai 165 and Saikai 168 bred from a highly resistant variety, Mudgo, were tested to evaluate the mechanism of resistance to the brown planthopper, Nilaparvata lugens STAL. The nymphs caged on the breeding lines at the early tillering stage did not exhibit a high mortality nor a low rate of adult emergence, but showed a slightly slower rate of growth than those on a susceptible variety, Asominori. The longevity of the adult females was similar between the breeding lines and the susceptible variety, but egg production on the breeding lines was reduced to 1/2-1/4 at the tillering stage of rice. The breeding lines were less preferred by the macropterous females both in the laboratory and in the field tests. In the field tests conducted in 1981 and 1983, the population density of the brown planthopper re-mained significantly low until harvest time in the breeding lines, while the density increased in the succeeding generation and hopperburn occurred in the susceptible variety. It is suggested that the mechanism of resistance resulting in the suppression of the planthopper population was mainly associated with non-preference and to some extent with antibiosis.
