RFLP Mapping Of Xa23, A Bacterial Blight Resistance Gene In Rice

Rice bacterial blight, caused by Xanthomonas oryzae pv. Oryzae (Xoo), is a destructive disease of rice in most rice-growing countries and caused much damage to yield and quality. The most efficient and economical way of controlling the disease is finding of the new bacterial blight resistance genes and using of variental resistance .The Xa23 resistance gene from Oryzae. rufipogon is a dominant gene, with high level of resistance at all growth stages and the broadest spectrum of resistance to bacterial blight. Fine-mapping is the first step for map-based cloning of it. A F2 population, with 2562 individuals, of JG30/CBB23, was constructed for molecular mapping of Xa23. In this study, the Xa23 resistance gene is maped with RFLP molecular marker 70N.The fragment length polymorphism(RPLP)marker(KJ03A), which is closely linked to rice blight resistance gene Xa23, was used to screen the transformation-competent artificial chromosome(TAC) library constructed from Minghui63, resulted in the detection of totally 21 positive clones, such as 3411, 45G1,70M12, 90L18, 37K24, 66M23, 77011. In this study, we analysed the positive clone 70M12 mainly. It' s left and right ends, named by 70B and 70N respectively, were islolated by Tail-PCR and plasmid rescue. In addition, we analysed the ploymorphism between the Xa23 near isogenic lines, CBB23 and JG30 and surved the ?2 susceptible individuals. The result showed a RFLP marker 70N closely linked to gene Xa23. The genetic distance between 70N and the gene Xa23 is 0.3cM.The plasmids of the 21 positive clones from Minghui63 TAC library were partially digested with Mbol or Sau3A, DNA size fractions ranging from 1Kb to 4Kb were ligased into vector pZERO-4 to construct a subclone library. We analysed the ploymorphism between the Xa23 near isogenic lines, CBB23 and JG30 with sucloned inserts as markers. The result showed the homology or non-homology between the subcloned inserts and CBB23 or JG30. The possible reason is that CBB23, JG30andMinghui63 originated from different genetic backgrounds.