RFLP MAPPING OF GENES CONFERRING COMPLETE AND PARTIAL RESISTANCE TO BLAST IN A DURABLY RESISTANT RICE CULTIVAR

Moroberekan, a japonica rice cultivar with durable resistance to blast disease in Asia, was crossed to the highly susceptible indica cultiva r, CO39, and 281 F-7 recombinant inbred (RI) lines were produced by si ngle seed descent. The population was evaluated for blast resistance i n the greenhouse and the field, and was analyzed with 127 restriction fragment length polymorphism (RFLP) markers. Two dominant loci associa ted with qualitative resistance to five isolates of the fungus were te ntatively named Pi-5(t) and Pi-7(t). They were mapped on chromosomes 4 and 11, respectively. To identify quantitative trait loci (QTLs) affe cting partial resistance, RI lines were inoculated with isolate PO6-6 of Pyricularia oryzae in polycyclic tests. Ten chromosomal segments we re found to be associated with effects on lesion number (P < 0.0001 an d LOD > 6.0). Three of the markers associated with QTLs for partial re sistance had been reported to be linked to complete blast resistance i n previous studies. QTLs identified in greenhouse tests were good pred ictors of blast resistance at two field sites. This study illustrates the usefulness of RI lines for mapping a complex trait such as blast r esistance and suggests that durable resistance in the traditional vari ety, Moroberekan, involves a complex of genes associated with both par tial and complete resistance.