Identification of a New Blast Resistance Gene in theindicaRice Cultivar Kasalath Using Japanese Differential Cultivars and Isozyme Markers

Rice blast is one of the most destructive diseases of rice. This study was undertaken to identify the rice blast resistance gene(s) in the indica rice cultivar Kasalath. 'Kasalath' was crossed with 9 of 12 Japanese differential cultivars, each carrying a single resistance gene at one of seven known loci. Allelism tests were performed in the F 2 populations with rice blast races. The resistance of 'Kasalath' was controlled by two dominant genes at different loci. The two resistance genes were nonallelic to the nine known resistance genes at six loci, Pi-a, Pi-i, Pi-k, Pi-ta, Pi-b, and Pi-t, and one of the genes was an allele of the Pi-z locus. For the gene detected at the Pi-z locus, an allelism test was performed using race 433.5, which is virulent to Pi-z t but avirulent to Pi-z. The results indicated that 'Kasalath' has the Pi-z t gene. To determine the location of the other gene, a linkage test using isozyme markers was performed with an F2 population segregating 3:1 (resistant/susceptible) when tested against race 477.1, which is virulent to Pi-z t . This gene was linked to Amp-3 (leucine aminopeptidase, EC 3.4.11.1) and Pgi-2 (phosphoglucose isomerase, EC 5.3.1.9) genes on chromosome 6 with recombination values of 37.6% ± 3.0% and 27.3% ± 2.7%, respectively. This gene was, therefore, designated Pi8.