GENETIC-CONTROL OF THE RESPONSE OF ERYSIPHE-GRAMINIS F SP HORDEI TO ETHIRIMOL AND TRIADIMENOL

A study was conducted on the genetic control of the response of Erysiphe graminis f.sp. hordei, the causal agent of barley powdery mildew, to two fungicides: the hydroxypyrimidine ethirimol, and the triazole, sterol demethylation inhibitor triadimenol. In tests of responses to both fungicides, sets of progeny of various crosses were classified by principal components analysis into discrete resistant and sensitive classes. A single allele controlled the response to ethirimol of the resistant isolate DH14 in crosses with the sensitive isolates CC52 and CC138. The ethirimol-resistance alleles of DH14 and another resistant isolate, CC107. are at the same locus or are closely linked. Alleles at single loci controlled resistance and sensitivity to triadimenol in crosses of DH14 (sensitive) with CC107 (moderately resistant) and CC138 (highly resistant). There was no evidence for polygenic control of response to either fungicide. The ethirimol response locus and the two putative triadimenol response loci are designated Eth1 and Tdl1 and Tdl2, respectively. There was no evidence for linkage of Eth1 and Tdl2 in the cross CC138 x DH14, in which responses to both fungicides segregated.