Genetic mapping of the powdery mildew resistance gene Pm6 in wheat by RFLPanalysis

Pm6 in bread wheat (Triticum aestivum L.), which was transferred from Triti cum. timopheevii L., is a gene conferring resistance to the powdery mildew disease caused by Erysiphe graminis f. sp. tritici. Six near-isogenic lines (NILs) of Pm6 in a cultivar 'Prins' background were analyzed to map this g ene using restriction fragment length polymorphism (RFLP). Each of the six NILs possessed a T. timopheevii-derived segment, varying in length, and ass ociated with powdery mildew resistance. Lines IGV1-465 (FAO163b/ 7*Prins) a nd IGV1-467 (Idaed 59B/7*Prins) had the shortest introgressed segments, whi ch were detected only by DNA probes BCD135 and PSR934, respectively. The po lymorphic loci detected by both probes were mapped to the long arm of chrom osome 2B. Lines IGV1-458 (CI13250/7*Prins) and IGV1-456 (CI12559/8*Prins) c ontained the longest I: timopheevii segments involving both arms of donor c hromosome 2G across the centromere. All these introgressed segments had an overlapping region flanked by the loci xspr934 and xbcd135 on 2BL. Thus, Pm 6 was located in this region since the powdery mildew resistance in all the NILs resulted from the introgressed fragments. Using the F-2 mapping popul ation from a cross of IGV1-463 (PI170914/7*Prins)xPrins, Pm6 was shown to b e closely linked to the loci xbcd135 and xbcd266 at a genetic distance of 1 .6 cM and 4.8 cM, respectively. BCD135 was successfully used in detecting t he presence of Pm6 in different genetic backgrounds.