ABSTRACT. Rice blast caused by Magnaporthe oryzae is one of the most devastating rice diseases worldwide. To understand the genetic diversity of indica landrace accessions and identify simple sequence repeat (SSR) markers that are associated with blast resistance, a population of 276 indica landraces from across the world was constructed. This population was then used to evaluate the blastresistance phenotype through artificial inoculation under controlled conditions in 2012 and 2013. The genetic diversity and association of the population with resistance were analyzed by examining the phenotype for 160 SSR markers distributed on 12 rice chromosomes. The 276 accessions were classified into seven groups using model-and distance-based cluster analyses. Associations between SSR markers and blast resistance showed that 26 SSR markers were significantly associated with blast resistance in 2012 and 2013 (P < 0.01) and that the phenotypic variation ranged from 2.68 to 13.11%. Nineteen of the markers associated with blast resistance were located in regions where genes or quantitative trait loci (QTLs) have been previously reported, and seven were newly identified in this study. These results indicate that marker-trait association has potential advantages over classical linkage analysis and QTL mapping, and that these markers could be used for marker-assisted selection in rice blast-resistance-breeding programs.

ABSTRACT. Bodao, a japonica landrace from the Taihu Lake region of China, is highly resistant to most Chinese isolates of Magnaporthe oryzea, a form of rice blast. To effectively dissect the influence of genetics on this blast resistance, a population of 155 recombinant inbred lines (F 2:8 ) derived from a cross of Bodao x Suyunuo was inoculated with 12 blast isolates. Using a quantitative trait locus (QTL) mapping approach, 13 QTL on chromosomes 1, 2, 9, 11, and 12 were detected from Bodao. Five QTL,, have not been previously reported. The qtl11-3-7 and qtl11-4-9 may be the two main effective QTL and resistant to 7 and 9 isolates, respectively. The results of the present study will be valuable for the fine mapping and cloning of these two new resistance genes.