The Pikm gene, conferring stable resistance to isolates of Magnaporthe oryzae, was finely mapped in a crossover-cold region on rice chromosome 11

The Pik(m) gene in rice confers a high and stable resistance to many isolates of Magnaporthe oryzae collected from southern China. This gene locus was roughly mapped to the long arm of rice chromosome 11 with restriction fragment length polymorphic (RFLP) markers in the previous study. To effectively utilize the resistance, a linkage analysis was performed in a mapping population consisting of 659 highly susceptible plants collected from four F-2 populations using the publicly available simple sequence repeat (SSR) markers. The result showed that the locus was linked to the six SSR markers and defined by RM254 and RM144 with approximate to 13.4 and approximate to 1.2 cM, respectively. To fine map this locus, additional 10 PCR-based markers were developed in a region flanked by RM254 and RM144 through bioinformatics analysis (BIA) using the reference sequence of cv. Nipponbare. The linkage analysis with these 10 markers showed that the locus was further delimited to a 0.3-cM region flanked by K34 and K10, in which three markers, K27, K28, and K33, completely co-segregated with the locus. To physically map the locus, the Pik(m)-linked markers were anchored to bacterial artificial chromosome clones of the reference cv. Nipponbare by BIA. A physical map spanning approximate to 278 kb in length was constructed by alignment of sequences of the clones anchored by BIA, in which only six candidate genes having the R gene conserved structure, protein kinase, were further identified in an 84-kb segment.