GENETICS OF RESPONSES TO MORPHOLINE-TYPE FUNGICIDES AND OF AVIRULENCES IN ERYSIPHE-GRAMINIS F-SP HORDEI

The genetics of the responses of the barley powdery mildew pathogen, E rysiphe graminis f.sp. hordei, to three morpholine-type fungicides wer e studied. Resistances to a phenylpropylamine fungicide, fenpropidin, and to a morpholine, fenpropimorph, co-segregated in crosses of a sens itive isolate, DH14, with each of two resistant ones, CC151 and CC152. In the cross CC151 x DH14, the results were consistent with resistanc e to both fungicides being controlled by a single gene, at a locus nam ed Fen1. In the other cross, CC152 x DH14, the genetics of resistance were more complicated; the data were cons;stent with the segregation o f two complementary, unlinked genes which each conferred resistance to both fungicides. Fenpropidin-resistant progeny of CC151 x DH14 were s ignificantly more resistant to fenpropimorph than were fenpropidin-res istant progeny of CC152 x DH14, although the resistant progeny of the two crosses did not differ significantly in their level of fenpropidin resistance. Fenpropidin-resistant progeny of CC151 x DH14 were signif icantly more resistant to another morpholine, tridemorph, than were fe npropidin-sensitive progeny, but this was not the case for CC152 x DH1 4. Resistance to triadimenol a C14 demethylation-inhibitor (DMI) fungi cide, segregated in both crosses. Triadimenol resistance appeared to b e controlled by one gene in each cross and was not associated with mor pholine resistance. CC151 x DH14 also segregated for eight avirulence genes. Two of these matched the Mla6 resistance, while one gene matche d a previously unknown resistance in a Pallas near-isogenic line, P17, which also carries a known resistance gene, MlK Fenl was not signific antly linked to the triadimenol resistance gene, Tdl(a), or to any of the eight avirulence genes. Avr(a6)l, Avr(a12), AVr(La), Avr(P17) and Tdl(a) were linked, as were Avr(a10) to and Avr(k).