Relationship Between RFLP Loci with Different Alleles on Chromosome 4 and the Levels of Blast Field Resistance in Japanese Upland Rice Varieties

Abstract

The QTLs, qBFR4-1 and qBFR4-2 confer field resistance to rice blast. The genetic locus controlling the resistance was mapped in a long arm region on chromosome 4 in the upland rice variety Kahei. The relationship between the level of blast field resistance and putative alleles at the qBFR4-1 and qBFR4-2 loci was analyzed using RFLP markers C600 and G271 that are the closest to each of the QTLs and by a field test for blast resistance among Japanese upland rice varieties. As a result, the upland rice varieties were divided into six varietal groups. Three major putative RFLP alleles (C600-a, C600-b and C600-c) were postulated at the C600 locus based on their fragment length, and the mean scores for blast field resistance of varieties with each allele were 2.81, 2.20 and 0.69, respectively. The C600-b allele was the most frequently observed in the Japanese upland varieties (46 %). Two major putative RFLP alleles (G271-a and G271-b) were postulated based on their fragment length, and the mean score for the resistance of varieties with each allele was 2.37 and 1.68, respectively. The varieties with the allele C600-c were the most resistant and the varieties with the alleles C600-c and G271-b showed the highest level of blast field resistance (0.58). On the other hand, the varieties with the allele C600-a and G271-a represented by the lowland variety Nipponbare showed the lowest level (2.98). These results suggest that the two QTLs for blast field resistance harbor two to three major alleles and that the levels of field resistance in upland rice varieties of Japan can be mainly assessed by the RFLP alleles tightly linked to the QTLs on chromosome 4. The RFLP markers used in this study seemed to be suitable for DNA marker-assisted selection of blast field resistance in rice breeding.