Development of DNA markers suitable for marker assisted selection of three Pi genes conferring resistance to multiple Pyricularia grisea pathotypes

Rice blast, caused by the fungus Pyricularia grisea (Cooke) Sacc., is a serious rice (Oryza sativa L.)disease causing considerable economic damage worldwide. DNA markers for rice blast resistance have been developed, but most are not suitable for routine use in a marker-assisted selection breeding program involving large numbers of progeny. After identifying candidate microsatellite markers from public database sources, we have mapped these markers near the blast resistance genes Pi-b, Pi-k, and Pi-ta(2) on rice chromosomes 2, 11, and 12, respectively, using segregation information from hundreds of progeny in several crosses. Two microsatellite markers, RM208 and RM224, were found to cosegregate with the Pi-b and Pi-k genes, respectively, while additional microsatellites were found to closely flank these two genes and the Pi-tal gene. The new markers are polymorphic in the narrow crosses characteristic of applied breeding programs and appear to be ideally suited for marker assisted selection for blast resistance in rice because of their tight linkage with resistance genes and ease of use through analysis of amplification products. A dominant marker indicating the presence of the Pi-b gene, Pibdom, has also been developed on the basis of the sequence of the cloned Pi-b gene. These markers should facilitate the introgression and pyramiding of these three blast resistance genes into new rice cultivars and elite lines.