LINKAGE ANALYSES OF RESISTANCE GENES TO BACTERIAL-BLIGHT IN RICE

Three resistance genes to bacterial blight (BB), xa-5, Xa-7 and xa-8, were genetically analyzed to identify their linkage groups and the loci. The gene xa-5 is known to be located on chromosome 5. The gene Xa-7 is also known not to be located only on chromosomes 3 and 11. Thus, the linkage analyses of xa-5 and Xa-7 were carried out with the marker genes located on chromosomes 5 and 3, respectively. The results showed that the xa-5 gene was linked with v-10 and spl-7 genes at recombination values of 37.7% and 8.8%, respectively. Similarly, the Xa-7 gene was linked with chl-3 and fc-1 genes at recombination values of 28.0% and 38.9%, respectively. On the other hand, the locus of xa-8 was estimated to be located on chromosome 2 or 3 by trisomic analysis. The allelic relationships between a mutant resistance gene, xa-15, and the other two mutant resistance genes, xa-19 and xa-20 were investigated. The reactions of F-1 plants to the BB races suggested that the xa-15 gene is nonallelic to both xa-19 and xa-20 genes.