The effectiveness of advanced rice lines with new resistance gene Xa23 to rice bacterial blight

摘要

Bacterial blight (BB) of rice is found world wide and particularly destructive in southeast Asia and China. The gene Xa4 has been incorporated in many rice cultivars and provided resistance to the disease in most of the rice growing countries in Asia. The gene also has been widely adopted in the development of indica hybrid and conventional rice for two decades in China. All of the restoring lines of indica hybrid rice carry the incomplete dominance gene Xa4 resulting to almost all of the combinations of indica hybrid being infected due to high disease pressure (Zhang Qi, 1991). Strains of BB that overcome the resistance of Xa4 has been reported in countries like the Philippines (Mew et al., 1982), Indonesia (Bustamam, pers comm.,); Eastern and Northern India (3/7 & 6/11 races virulent) Vietnam (Quang, pers comm.); Nepal (Adhikari et al., 1999) in these countries except Eastern and Northern India such strains represent the dominant population. Although Xa4 has residual resistance, breeders preferto use the gene Xa21 with broader spectrum resistance in rice when it was identified and cloned by Khush et al. 1990 and Song et al. 1995, respectively. Unfortunately, for Xa21, certain groups of strains can overcome the resistance conveyed by Xa21, such as race 10 of the Philippines and some strains in Korea, Indonesia, Japan, and China.