Recent Status in Virulence to Resistant Rice Varieties of Brown Planthopper Nilaparvata lugens Immigrating into Japan

Abstract

Virulence of the brown planthopper Nilaparvata lugens that immigrated into Japan in 1991, 1992, 1995 and 1996 was examined on four indica rice varieties, IR26 (carrying a resistance gene Bph-1), Mudgo (Bph-1), ASD7 (bph-2) and Babawee (bph-4) and on two japonica rice lines, Saikai 190 (Bph-1) and Norin PL10 (Bph-3). The planthoppers were reared on a susceptible japonica rice variety Reiho, and the newly-emerging brachypterous females were released on 5-to 7-week-old test rice plants at tillering stage. I defined the females whose abdomina became swollen within five days after releasing or those which have survived for five days as virulent individuals. The 1995- and 1996-populations of N. lugens had higher proportions of virulent females on the Bph-1-carrying rice varieties, 54-79% on IR26, 39-66% on Mudgo and 95% on Saikai 190, than the 1991- and 1992-populations. However, all the tested populations had still low proportions of virulent females on the rice varieties carrying bph-2, Bph-3, or bph-4, especially those carrying Bph-3 or bph-4. These results show that virulence to Bph-1 in the N. lugens populations immigrating into Japan has become stronger after 1988-1990 in which change of the virulence was first found, and suggest that the resistance of Bph-1 has been broken down for this N. lugens population.