| Rice is one of the most important cereal crops, which provides stable food for about half of the global population. Bacterial blight of rice, which is a vascular bundle disease caused by Xanthomonas oryzae pv. oryzae (Xoo) , is one of the most serious diseases of rice worldwide, and leads the yield of rice reduced by 10%-20%. It has been proved that breeding resistant varieties of rice is the most effective and economical method to control rice bacterial blight. But because of the evolution of pathogenic bacteria, the resistance of some resistant varieties, which carry less resistance genes with narrow antibiogram, may be overcome by newly evolved pest types in the several years or shorter after their cultivating. So, seeking and using new bacterial blight resistance genes have become more and more important. Lin et al. in 1996 identified a gene Xa22(t) resistant to pest types of Xoo including Pxo6l in an indigenous rice variety Zhachanglong (ZCL) from Yunnan Province of China, and located it to the distal end on the long arm of chromosome 11.The attempt of this study, reported in this paper, is to further determine the ZCL resistance to different pest types of Xoo, and construct the fine and physical maps of the bacterial blight resistance genes in the ZCL so as to finally clone them. The main results are as follows:1. The 301 F3 random families and 303 F3 extremely Pxo61-susceptible families from the F2 plants of the original cross between ZCL and Zhengzhu Ai (ZZA) were inoculated with 2 different strains, Pxo6l and OS 105, at the booting stage. After 20 days, the lesion length was measured and the data was analyzed.(1) In the 303 F3 extremely families, all families were susceptible to Pxo61. And in the 301 F3 random families inoculated with Pxo6l, the segregation of resistance and susceptibility to Pxo6l occurred and the segregation ratio of homozygous resistant families: heterozygous resistant families: homozygous susceptible families approximated to 1: 2: 1 Cr= 0.1097, P= 0.95-0.90). It was further demonstrated that there was only one dominant resistance gene, Xa22(t), determining the resistance against Pxo61 in ZCL.(2) In the 303 F3 extremely Pxo6l-susceptible families inoculated with OS105, there appeared a segregated ratio of 1 (homozygous OS105-resistant families): 2 (heterozygous resistant families): 1 (homozygous OS105-susceptible families) (x2 = 0.8463, P= 0.70-0.50). However, in the 301 F3 random families inoculated with OS105, the ratio became 7: 8: 1 (x2= 0.678, p = 0.80-0.70). This meant that there are 2 resistance genes against OS 105 in ZCL, one of which is Xa22(t), resistant to both Pxo61 and OS 105, and another is susceptible to Pxo6l but resistant to OS 105.2. In 332 RFLP markers randomly selected from the RFLP molecular marker linkage maps of rice genome covering all the 12 chromosomes, there were 102 RFLP markerswith polymorphism between the parents (ZCL and ZZA). And only 14, located on chromosome 11, of the 102 markers were linked to the resistance gene against Pxo6\. Moreover, the number of the markers with polymorphism on different chromosomes were not equally distributed, over 50% on chromosomes 4, 5 and 11, 12.9% and 5.9% on the chromosomes 3 and 6 respectively.3. By the method of RFLP analysis on random F2 population including 248 plants randomly selected from a very large F2 population (>2000 plants) from the cross of ZCL and ZZA, the 14 RFLP markers on chromosome 11 linked with Xa22(i) were located on the distal end of long arm of chromosome 11 with a genetic distance shorter than 7 cM. And Xa22(t) cosegregated with the RFLP marker R1506 and flanked by Y6855RA and G2132B with the distance of 1.1 cM between them. In the extremely Pxo6l-susceptible F2 population including 404 plants there was 1 recombination event identified between the frank marker Y6855RA and Xa22(i). And no recombination events were observed between the RFLP marker R1506 and Xa22(t). This result further demonstrated that Xa22(t) cosegregated with the RFLP ma...
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