Physiologic specialization of puccinia recondita f. sp. tritici in canada in 1993

In 1993, leaf rust of wheat (Triticum aestivum) caused by Puccinia recondita f. sp. tritici was first observed during the second week of June in winter wheat fields in southern Manitoba. Lower than normal summer temperatures reduced the development of the disease on spring wheat throughout western Canada in 1993. The wheat cultivars Columbus, Roblin, Pasqua, and Minto remained highly resistant to leaf rust in 1993 and losses due to leaf rust in these cultivars were minimal. Light severity levels were found in fields of Biggar and Katepwa. A total of 36 virulence phenotypes of the fungus in Canada were detected using 16 isogenic Thatcher differential lines. Phenotypes with virulence to resistance genes Lr3ka and Lr30 increased from less than 1% in 1992 to over 40% in 1993 in Manitoba and Saskatchewan. Virulence frequencies to Lr2a, Lrl 1, Lr24, and Lr26 were between 40%-60% in Manitoba and Saskatchewan. The prevalent phenotype in Quebec and Ontario remained unchanged from previous years, with avirulence to Lr2a and virulence to Lr3ka.