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We searched for blast resistance genes in an Indica-type rice (Oryza sativa L.) cultivar, Kasalath. The resistance gene was estimated based on the reaction patterns to standard differential blast isolates from Japan and Philippines against the monogenic lines as differential varieties targeting 24 kinds of resistance genes. Kasalath showed complete resistance only to a Japanese isolate, Hoku1, which was avirulent to genotypes containing the Piz allele genes and virulent to genotypes containing Pia and Pish. Kasalath was susceptible, or only moderately resistant, to the Philippine isolates. A QTL analysis for resistance to Hoku1 was performed in backcross inbred lines derived from crosses between Kasalath and a Japonica-type cultivar, Nipponbare (recurrent parent), harboring Pia and Pish. A resistance QTL with the Kasalath genotype was detected in the same region as Pia on chromosome 11. Association analysis in 50 chromosome segment substitution lines detected three associations, on chromosomes 6, 8 and 11; the association located in the same region as the QTL on chromosome 11 had a strong resistance effect. These reaction patterns indicated that Kasalath did not harbor Pia and that the QTL on chromosome 11 was the other allele of Pia or a novel resistance gene. [ABSTRACT FROM AUTHOR]