Résumé
In addition to being one of the most acute problems impeding chemical
control of fungal diseases, the evolution of fungicide resistance is an
emblematic case of local adaptation to spatially heterogeneous and
temporally variable selection pressures. Here we dissected the adaptation
of Botrytis cinerea (the causal agent of grey mould) populations on grapes
to several fungicides. We carried out a 2-year survey (four collection
dates) on three treated/untreated pairs of plots from vineyards in
Champagne (France) and monitored the frequency of four resistant
phenotypes that are unambiguously associated with four distinct genotypes.
For two loci under selection by currently used fungicides (MDR1 and MDR2),
the frequencies of resistant mutations at vintage were greater in treated
plots compared to untreated plots, showing that the effect of selection is
detectable even at the plot scale. This effect was not detectable for two
other loci under selection by previously used fungicides (BenR1 and
ImiR1). We also found that treatment with currently used fungicides
reduced B. cinerea effective population size, leading to a significant
decrease in genic diversity and allelic richness in treated vs. untreated
plots. We further highlight that even under ample drift and migration,
fungal populations can present an efficient response to selection.
Finally, for the four studied loci, the costs of fungicide resistance were
estimated by modelling the decrease in the frequency of resistant
mutations in the absence of treatment. We discuss the importance of these
estimates for defining strategies for limiting or counteracting the local
adaptation of pests to fungicides.