POWDERY MILDEW RESISTANCE IN WINTER-WHEAT .2. IDENTITY OF RESISTANCE GENES

Gene number and mode of inheritance of powdery mildew resistance in 10 wheat (Triticum aestivum L.) lines was determined in a previous report. However, the allelic relationships of these genes to each other and to known genes was not determined. Eight of the 10 powdery mildew resistant wheat lines were crossed with each other and to each of 13 host differential lines that have known genes for resistance to powdery mildew, caused by Blumeria graminis (DC.) E. O. Speer f. sp. tritici Em. Marchal. In each cross, 300 to 800 F-2 seedlings were evaluated for their reaction to isolate 127 of B. graminis f. sp. tritici in the greenhouse to determine the relationship and putative identity of resistance genes in the eight lines. One common gene, Pm4b, was identified in the wheat lines C39, A55-2, R107, 'Armada', and SI5. The three genes in C39 and SI5 were identified as Pm2, Pm4b, and Pm6 based on lack of susceptible progeny from crosses of these lines with the corresponding host differentials. The resistance genes in OK75R3645 and GO4779 differ from each other and from those identified in the other resistant lines. The resistance gene in OK75R3645 most likely is an allele or closely linked to the Pm3 locus. It is probable that the resistance gene in GO4779 is Pm1, as no segregation for susceptible progeny was observed in the cross of GO4779 with the differential line Axminster/8*CC(Pm1). A single recessive gene, pm8, was postulated for ST1-25, whose disease reaction was intermediate to isolate 127. Six different genes governing resistance to powdery mildew were identified among the eight wheat lines, and Pm4b was the most common gene.