GENETIC CORRELATIONS IN RESISTANCE TO MORPHOLINE AND PIPERIDINE FUNGICIDES IN PYRENOPHORA-TERES POPULATIONS

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 o f Pyrenophore teres in North America and Europe which had not been pre viously exposed to these fungicides. Resistance phenotypes were contin uously distributed for each fungicide in each population. Cross resist ance relationships were determined by estimating genetic correlation c oefficients 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%) coeff icients were not significantly different from 1 (P > 0.05). This resul t is consistent with the hypothesis that many of the same genes, or ge nes in gametic disequilibrium, control resistance to more than one fun gicide in most populations of P. teres and that these fungicides compr ise a single cross resistance group. Three of 36 (8%) correlation coef ficients were not significantly different from 0 (P > 0.05) indicating that, in these populations, independent genes controlled resistance t o these fungicides. The results of this study indicate that although m ost of the same genes control resistance to morpholine and piperidine fungicides in P. teres, differences in frequencies of these genes amon g populations can result in different cross resistance relationships f rom one population to another.