Identification of a RFLP marker tightly linked to the panicle blast resistance gene, Pb1, in rice.

We precisely mapped the Pb1 locus for the panicle blast resistence of a quantitative nature on rice chromosome 11 using RFLP markers. Based on the cosegregation of the resistant genotypes of Pb1 and Stvb-i, a rice stripe virus (RSV) resistance gene derived from an Indica cultivar Modan, we examined the linkage relationships between Pb1 and 13 Stvb-i-linked RFLP markers located on the long arm of chromosome 11. The Pb1 locus was mapped in the Modan-derived chromosomal region in the middle part of the long arm of chromosome 11. Pb1 was located on the telomere side in relation to the Stvb-i locus. The Pb1 gene was closely located at 1.2cM from three RFLP markers: S723, CDO226, C189. Then, we examined the graphical genotypes of 34 Modan-derived RSV-resistant cultivars with or without panicle blast resistance, and 12 susceptible Japonica cultivars, using 21 RFLP markers. Among them, cultivars with panicle blast resistance were classified into four types: A, B, C and D, and those without it into six types: E, F, G, H, I and J. In all of the panicle blast-resistant cultivars, the Modan-type bands were observed in S723, CDO226 and C189. On the other hand, in all the panicle blast-susceptible cultivars, the Japonica-type band was observed in S723, whereas the Modan-type bands were noticed in CDO226 and C189 in Type E cultivars. Consequently, only the genotypes of the S723 locus completely coincided with the genotypes of the Pb1 locus. Although, it was determined, based on linkage analysis, that S723, CDO226 and C189 were located at the same locus, graphical genotyping analysis, using many progeny cultivars derived from Modan, revealed that S723 was the closest marker to Pb1 among the three.