Inheritance and mechanisms of resistance to anilinopyrimidine fungicides in Botrytis cinerea (Botryotinia fuckeliana)

Monitoring conducted in French vineyards since 1994 led to detection of thr ee anilinopyrimidine-resistant phenotypes in field populations of Botrytis cinerea (Botryotinia fuckeliana). A few strains were highly resistant to an ilinopyrimidines (e.g., pyrimethanil) only and were named Ani(R1). Analysis of tetrads obtained from crosses between Ani(R1) and sensitive strains (An i(s)) showed that one major gene is probably involved in the Ani(R1) phenot ype. The resistance mechanism has not yet been elucidated but the Ani(R1) s trains did not seem to display a reduced accumulation of [C-14]pyrimethanil in their mycelium. We also distinguished two different patterns of cross-r esistance, named Ani(R2) and Ani(R3) phenotypes. Both were weakly resistant to anilinopyrimidines, highly resistant to tolnaftate, a squalene epoxidas e inhibitor (used only in medicine), and appeared less sensitive to dicarbo ximides (e.g., iprodione). Moreover, Ani(R2) strains were weakly resistant to phenylpyrroles (e.g., fludioxonil) while Ani(R3) strains displayed a sli ght decrease of sensitivity to sterol C14-demethylation inhibitors (e.g., p rochloraz, tebuconazole) and to the experimental hydroxyanilide fenhexamid. Genetic analysis showed that there is no disjunction of multiple resistanc es in ascospore progenies and we found a 1:1 segregation of sensitive:resis tant phenotypes, suggesting that Ani(R2) and Ani(R3) phenotypes are each pr obably encoded by a single major gene. Studies on the uptake of [C-14]pyrim ethanil did not show any difference between the sensitive and the resistant strains. However, the addition of fluazinam, an uncoupler, led to an accum ulation of the fungicide in mycelium, suggesting that an active efflux occu rred. Experiments carried out on the uptake of [C-14]tebuconazole and [C-14 ]triadimenol, two sterol C14-demethylation inhibitors, showed a lower accum ulation of these fungicides in mycelium of resistant strains than in sensit ive strains. The effect of fluazinam demonstrated that this phenomenon was correlated with an energy-dependent efflux, which seemed to be inducible in sensitive strains and constitutive in resistant strains and could be a mul tidrug resistance mechanism. (C)1999 Academic Press.