31. The effectiveness of advanced rice lines with new resistance gene Xa23 to rice bacterial blight
  Q. ZHANG1, C.L. WANG1, K.J. ZHAO1, Y.L. ZHAO1, V.C. CASLANA2, X.D. ZHU3, D.Y. LI4 and Q.X. JIANG5

1)Institute of Crop Breeding and Cultivation, CAAS, Key Laboratory of Crop Genetics & Breeding, Ministry of Agriculture , The People's Republic of China , Beijing 100081, China
2)International Rice Research Institute, DAPO 7777 Metro P.O. Box 933, Manila, Philippines
3)China National Rice Research Institute, Hangzhou 310006, China
4)Institute of Germplam Resources, GAAS Naining 530007, China
5)Institute of Rice and Wheat Breeding, Wujin 213149, China

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 prefer to 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.

We identified and tagged a new gene for resistance to BB and designated as Xa23 from O. rufipogon (Zhang Qi et al. 1998). This new gene demonstrated the broadest spectrum of resistance to BB. To further compare the spectrum of resistance to BB between the two genes, Xa21 and Xa23, 20 strains including 10 Philippine races, 7 Chinese pathotypes, and 3 Japanese races were used to inoculate plants at maximum tillering stage (MTS) in 2001 in Beijing. The CBB23 (carrying Xa23) is highly resistant to the all 20 strains including Philippine race 10, while IRBB21 (carrying Xa21) is resistant to 19 strains, but and high susceptible to the Philippine race 10. The results on Xa21 confirmed the findings at IRRI (Madamba et al. 2000) and are similar with IRRI tested in 2000 (Vera Cruz C.M.). It is therefore clearly that Xa23 has the broadest spectrum

resistance to BB designated so far (Table 1).

The effectiveness of resistance to BB in advanced rice lines with gene Xa23

The gene Xa23 not only has the broadest resistance spectrum to races in the Philippines, Japan and China, but also shows highly level of resistance at all growth stages and has strong efficiency of inheritance for resistance. Since 1989, the resistance donor, RBB16, an accession from O. rufipogon, and H4, the anther-cultured line derived from cross of JG30/RBB16 were introduced into some susceptible varieties: Japonica Zhongzuo 180 with high yielding ability, 9520 with high yielding, good quality and resistance to blast; and indica varieties, IR24, NJ11, and Zhengzuai with improved plant type, and a restoring line of hybrid rice, Longtep. The resistance evaluation was made with the specific strain PXO99 for all progenies of the crosses until advanced line. The lines were highly resistant to the strain at all growth stages (Table 2)

The resistance with high level and broad spectrum to BB derived from Xa23 has been inherited strongly into all of the progenies and advanced lines. Obviously, the new gene Xa23 will contribute to widening the genetic background for resistance to BB and serves as additional resistance genetic resource by turns in rice breeding program in the world.


This project is supported by grants from the Rockefeller Foundation (No 97001 #258 ) and the National Natural Sciences Foundation of China, (No. 39670508)


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