Identification and characterization of a new blast resistance gene located on rice chromosome 1 through linkage and differential analyses

The Chinese native cv. Q14 expresses a high level of resistance to many isolates of Pyricularia grisea collected from Japan, Thailand, and China. Q14 was crossed to an indica-susceptible cultivar, Q61 . To rapidly determine the chromosomal location of the major resistance gene present in the cultivar, a linkage analysis using microsatellite markers was performed in the F-2 population segregating 3R:1S (resistant/susceptible) through bulked-segregant analysis (BSA) in combination with recessive-class analysis (RCA). A total of 189 microsatellite markers selected from each chromosome equally (with approximate to10 centimorgans) were tested with the BSA approach. Only two markers. RM151 and RM259, located on chromosome 1 showed positive and negative polymorphisms, respectively, for a resistance gene segregating in the population. To confirm the polymorphic markers, a total of 155 viable susceptible individuals were tested with the RCA approach. The markers RM151 and RM259 were found to link to the resistance gene with recombination frequencies of 11.9 +/- 2.8% and 9.7 +/- 8.0%, respectively. For further characterization of the resistance gene, 3 resistance genes mapped on chromosome 1, as well as 15 major resistance genes that might be employed in the breeding program, were selected for differential tests with 85 Chinese isolates. The resistance gene identified in this research conveys reactions distinct front those conditioned by the 18 resistance genes. This new resistance gene tentatively was designated Pi27(t).