Genetic correlations in resistance to morpholine and piperidine fungicides inPyrenophora teres populations

Abstract

Highly significant genetic variation (P < 0.001) in resistance to the morpholine fungicides fenpropimorph, tridemorph and dodemorph and the piperidine fungicide, fenpropidin was found in different populations of Pyrenophore teres in North America and Europe which had not been previously exposed to these fungicides. Resistance phenotypes were continuously distributed for each fungicide in each population. Cross resistance relationships were determined by estimating genetic correlation coefficients in resistance to all pairwise combinations of fungicides. The majority of the correlation coefficients were highly positive for all fungicide combinations in all populations; eight of 36 (22%) coefficients were not significantly different from 1 (P > 0.05). This result is consistent with the hypothesis that many of the same genes, or genes in gametic disequilibrium, control resistance to more than one fungicide in most populations of P. teres and that these fungicides comprise a single cross resistance group. Three of 36 (8%) correlation coefficients were not significantly different from 0 (P > 0.05) indicating that, in these populations, independent genes controlled resistance to these fungicides. The results of this study indicate that although most of the same genes control resistance to morpholine and piperidine fungicides in P. teres, differences in frequencies of these genes among populations can result in different cross resistance relationships from one population to another.