Three Loci in Wheat Involving Resistance to Erysiphe graminis f. sp. tritici1

With the advent of high yielding, strong straw, semi‐dwarf varieties of wheat, growers have increased rates of fertilizer, particularly nitrogen, and are producing more wheat under irrigation. Consequently, losses caused by Erysiphe graminis tritici have increased. Breeding for resistance is the only practical means of control. Of 23 resistant varieties or selections studied, 11 apparently had in common a gene designated Pml (formerly Ml 1 ). Four had Pm2 (formerly Ml u ) and eight had Pm3 (formerly Ml s , Ml a , or Ml c ). Some varieties or selections within each group could be differentiated by appropriate Erysiphe graminis f. sp. tritici cultures. Either a series of multiple alleles occurred at each of the three loci or other genes for resistance were present but not revealed by cultures 3, 22, and 27. Additional tests designed to establish or refute presence of multiple alleles are underway. Data from intercrosses between varieties or selections representing the three loci indicate independence of genes for resistance. A multiple allelic series presents restrictions on combining specific genes for resistance under conventional breeding methods. Utilization of two alleles simultaneously is possible with hybrid wheat.