Thiophanate‐methyl and carbendazim resistance in Fusicoccum amygdali , the causal agent of constriction canker of peach and almond

International audienceIn light of growing environmental concerns, surveys of fungicide resistance are needed to ensure efficient control of fungi and avoid unnecessary treatments. Investigations of fungicide resistance in Fusicoccum amygdali are scarce despite the economic impacts of this pathogen in peach and almond orchards. Thiophanate-methyl has been registered for more than 20 years to control F. amygdali but no resistance has been reported to date. This propesticide is metabolized by fungi into carbendazim, a β-tubulin inhibitor. Sensitivity to carbendazim of nine populations of F. amygdali from French orchards was assessed using germination bioassays. Also, resistance levels of 63 strains isolated from four populations were evaluated using mycelial growth assays. The underlying mechanism of resistance was investigated by sequencing the β-tubulin gene, the molecular target of thiophanate-methyl, in a set of isolates with different levels of sensitivity to carbendazim. Cross-resistance to thiophanate-methyl and to another β-tubulin inhibitor, diethofencarb, was also assessed in carbendazim-sensitive and -resistant strains. Isolates highly resistant to carbendazim were found in one of the nine orchards studied. Sequencing showed that resistant phenotypes carry a mutation in the β-tubulin gene leading to E198K substitution. Positive cross-resistance to thiophanate-methyl was confirmed and no negative cross-resistance to diethofencarb was identified in the phenotyped isolates, which were all resistant to this active substance. To our knowledge, this is the first report of resistance to thiophanate-methyl in F. amygdali. The high level of resistance of isolates sampled in one population is of concern, although the limited geographical scope of resistance suggests its recent emergence

Tavelure du pommier sa résistance aux strobilurines en France - Tests biologiques et moléculaires 2004-2006

National audienceDans la lutte chimique contre la tavelure, il est essentiel de savoir si l'agent de la maladie présente une résistance à certains des fongicides utilisés. D'où la surveillance évoquée dans cet articl

Status of resistance towards SDHIs in French populations of Sclerotinia sclerotiorum and characterization of resistant strains

International audiencePopulations of fungal pathogens may be subject to many selective pressures in agricultural environments. Among them, fungicides constitute one of the most powerful determinants of population adaptation acting in a short time span. Here, we investigated whether fungicides sprays applied yearly in the Champagne vineyard to control the grey mold causal agent Botrytis cinerea could shape population structure and evolution. We carried out a 2-year survey (4 collection dates) on three treated/untreated pairs of plots. We found that fungicides treatments had no or little impact on population subdivision at neutral loci, as well as on diversity or reproduction mode. Nevertheless, we found evidence of stronger genetic drift in some treated plots, consistent with the regular application of fungicides. Moreover, we observed spatial structure in resistance frequency for two loci under contemporary selective pressure, as reflected by cline patterns. At last, using a modeling approach, we estimated fitness costs of resistance to fungicides, responsible for resistance frequency decay during winter. Further work is in progress to estimate parameters of positive selection and migration exerted on B. cinerea populations, and disentangle the relative effect of the evolutionary forces at work