The gene
Pi15 for resistance of rice to
Magnaporthe grisea
was previously identified as being linked to the gene
Pii. However, there is a debate on the chromosomal position of the
Pii gene, because it was originally mapped on chromosome 6, but recent work showedit might be located on chromosome 9. To determine the chromosomal location of the
Pi15 gene, a linkage analysis using molecular markers was performed in a F2 mapping population consisting of 15 resistant and 141 susceptible plants through bulked-segregant analysis (BSA) in combination with recessive-class analysis (RCA). Out of 20 microsatellite markers mapped on chromosomes 6 and 9 tested, only one marker, RM316 on chromosome 9, was found to have a linkage with the
Pi15 gene with a recombination frequency of (19.1 ±3.7)%. To confirm this finding, four sequence-tagged site (STS) markers mapped on chromosome 9 were tested. The results suggested that marker G103 was linked to the
Pi15 gene with a recombination frequency of (5.7 ±2.1)%. To find marker(s) more closely linked to the
Pi15 gene, random amplified polymorphic DNA (RAPD) analysis was performed. Out of 1 000 primers tested, three RAPDmarkers, BA
Pi15486,BA
Pi15782and BA
Pi15844were found to tightly flank the
Pi15 gene with recombination frequencies of 0.35%, 0.35% and 1.1%, respectively. These three RAPD markers should be viewed as the starting points for marker-aided gene pyramiding and cloning. A new gene cluster of rice blast resistance on chromosome 9 was also discussed.
