This study was conducted to investigate the resistance reaction of single resistance genes and their pyramiding effectsin indica and japonica rice against bacterial blight disease in Korea. Resistance reaction of indica and japonica near-isogeniclines and pyramided lines carrying resistance genes to four predominant and other sixteen bacterial blight isolates was investigated.Among singe resistance genes, Xa1, Xa3, and Xa21 in indica and japonica near-isogenic lines exhibited same or similar resistancereaction. On the other hand, Xa4 and xa5 showed higher resistant reaction in indica background than in japonica background.Combined resistance genes provided the pyramiding effects such as increasing the resistance relative to single gene or two genesand the complementation of susceptibility in both indica and japonica rice. Newly identified combinations in japonica rice,Xa3+Xa21, xa5+Xa21, and Xa3+xa5+Xa21, conferred resistance to all isolates and showed higher resistant reaction than Xa3+xa5widely used in Korea. These could be the efficient and promising combinations for enhancing the resistance of japonica riceand delaying the breakdown of resistance against Xanthomonas oryzae pv. oryzae in Korea.
