The indica-derived rice blast resistance genes Pi-ta2 and Pi-ta, introgressed into a japonica background, were mapped on the middle of chromosome 12 with restriction fragment length polymorphism (RFLP)/random amplified polymorphic DNA (RAPD) markers and several nearly isogenic lines (NILs). Pi-ta2 cosegregated with XNpb 289 and 196, and was flanked by closely linked markers at 0.3 (ta2-1) and 0.7 cM (XNpb 088, 319/079) on the left (up) side, and at 0.3 (RUBss) and 0.7 cM (XNpb316) on the right (down) side of the map, in F2 analyses of Pi No. 4 × japonica crosses, with 160 recessive homozygotic individuals corresponding to 320 chromosomes. CHEF (contour-clamped hexagonal electric field) Southern blotting suggested that XNpb088 and XNpb239-1, both very close to Pi-ta2, were spanned by a 170-kb band, suggesting about 500 to 750 kb/cM as the physical/genetic distances ratio in the crosses of Pi No. 4 × japonica, which was rather low in recombination ratio, in this region. Pi-ta was mapped to the position overlapping Pi-ta2 by graphical genotype analysis of an NIL with a very narrow introgressed region, Shimokita. This result suggested that these functionally related genes are allelic or at least very closely located, and that they may be derived from a common ancestral gene. However, RFLP analyses of the NILs of these two genes indicated that they are derived from rather different genomes, refuting the report that NILs of Pi-ta share a common donor with those of Pi-ta2. This indicates that the two genes differentiated at a rather ancient time. Two other pedigrees, describing spontaneous recent origins of Pi-ta in japonica, were also refuted and a single indica origin of the gene was indicated.

No abstract

No abstract

No 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.