Competition Between Triadimefon-Sensitive and Triadimefon-Resistant Isolates of Erysiphe graminis f. sp. tritici . Khalil I. AlMughrabi, Department of Biology, Nova Scotia Agricultural College, P.O. Box 550, Truro, Nova Scotia, Canada B2N 5E3. A. Bruce Gray, Department of Biology, Nova Scotia Agricultural College, P.O. Box 550, Truro, Nova Scotia, Canada B2N 5E3. Plant Dis. 79:709-712. Accepted for publication 4 April 1995. Copyright 1995 The American Phytopathological Society. DOI: 10.1094/PD-79-0709.

The competitive abilities of randomly selected triadimefonsensitive (S) and triadimefonresistant (R) singlepustule derived isolates of Erysiphe graminis f. sp. tritici obtained from triadimefontreated and untreated fields of the Annapolis Valley (AV), Nova Scotia, were tested. In 1991, mixed inoculations of S/R isolates in 75:25, 50:50, and 25:75 ratios were studied in vitro in the absence of triadimefon on wheat cultivar Absolvent. In 1992, a 50:50 (S/R) inoculation ratio was used to study the competition between R and S isolates collected from triadimefontreated fields in the AV. Results indicated that in the absence of triadimefon the mean EC5U values of mixtures of various S/R ratios tested in 1991 and of the 50:50 ratio tested in 1992 decreased significantly (P < 0.05) after five generation cycles. Resistant isolates were less fit (less competitive) than sensitive ones in the absence of triadimefon

Keyword(s): Bayleton, demethylation inhibitor, fitness of resistant strains, triazole