Abstract
Biotypes cause a serious problem in controlling brown planthopper (BPH), Nilaparvata lugens Stål (Homoptera: Delphacidae). We characterized four BPH strains, which were collected in different localities in Japan and maintained by random mating within each strain for different periods. The virulence of the BPH strains was evaluated based on their postembryonic development on susceptible and resistant rice lines and inhibition of rice seedling growth. Two single resistance gene introgression lines, “Norin-PL3 (Bph1 carrier)” and “Norin-PL4” (bph2 carrier), and a pyramided line in which both genes were combined were used with a susceptible japonica recurrent parent “Tsukushibare” as a control. Sequence comparison of the mitochondrial cytochrome oxidase-I (COXI) gene was also performed in the characterization. The four BPH strains were classified into two or three groups with unique virulence spectra. The oldest strain showed avirulence against both introgressed resistance genes, while the three younger strains showed strong virulence against one or both genes. The different virulence spectra suggested the sequential adaptation of these BPH strains to the two resistance genes. Pyramiding of the resistance genes had no additive effect on rice seedlings carrying them even against avirulent and less-virulent BPH strains.
