Characterization of fungicide sensitivity profiles of Botrytis cinerea populations sampled in Lombardy (Northern Italy) and implications for resistance management

Abstract

BACKGROUND: Resistance to fungicides is one of the aspects that must be considered when planning treatments to achieve an optimal control of grey mold, caused by Botrytis cinerea, in vineyards. In this study, extensive fungicide resistance monitoring was carried out in Northern Italy (Lombardy region) to evaluate several aspects of fungicide resistance (frequency of resistance, effect of field treatments, mechanism of resistance and fitness) on 720 B. cinerea strains isolated from 36 vineyards.RESULTS: Of the characterized strains, 12% were resistant to a single fungicide class (3% to the succinate dehydrogenase inhibitor boscalid, 4% to the anilinopirimidine cyprodinil; 5% to the phenylpirrole fludioxonil; 0.1% to the ketoreductase inhibitor fenhexamid) and 0.8% to two fungicide classes contemporaneously. Resistance was associated with mutations reported in the literature for boscalid (H272Y/R) and fenhexamid (P238S or I232M). Two new mutations in sdhC (A187F) and in sdhD (I189L) could be related to boscalid resistance. Strains resistant to fludioxonil did not show any known mutations. No significant differences were found in the fitness of sensitive and resistant strains. CONCLUSION: Overall, field populations of B. cinerea showed a relatively low frequency of resistance, but the geographical distribution of resistance, genetic mechanisms of resistance and fitness of resistant strains suggest that management of resistance should be implemented, at local and regional levels. Particular attention should be given to the fungicide sprays planned before veraison, since they seem to be associated with a higher frequency of resistant strains in vineyards.

Fungicide resistance characterised across seven modes of action inBotrytis cinereaisolated from Australian vineyards

“…The P238S mutation identified in fenhexamid sensitive and resistant isolates in this study (Fig. 6), has been found in both sensitive and resistant isolates in a number of grape and non-grape studies, which suggests that P238S may not be associated with resistance (Albertini and Leroux 2004;De Miccolis Angelini et al 2014;Esterio et al 2011;Grabke et al 2012;Toffolatti et al 2020).…”

“…Frequency discrepancies between this study and previous reports could be the result of differences in phenotyping methodology. This study used microtiter and YSSA based mycelial growth methods to calculate overall frequencies, while previous reports used either microtiter (Campia et al 2017;Leroch et al 2011;Toffolatti et al 2020) or a non-YSSA based mycelial growth methods (Avenot et al 2018;Banno et al 2009;Beresford et al 2017;Latorre and Torres 2012;Lu et al 2016;Sergeeva et al 2002a;Yin et al 2015) (Table 4).…”

Bacillus amyloliquefaciens strain QST713 may contribute to the management of SDHI resistance in Botrytis cinerea

“…SDHIs were selected as the target-fungicide group since they represent the most rapidly expanding group used against B. cinerea and problems with resistance development to this fungicide class have already been developed in Mediterranean countries. [6][7]13,31,35 The introduction of several SDHI molecules into the practice either as botryticides or against other diseases such as powdery mildew along with the differential effect of the several known sdh mutations on the sensitivity to different SDHIs makes the implementation of antiresistance strategies more complex. Moreover, it has been shown that sdhB mutants may suffer fitness penalties 8,10 and thus reduction of SDHI selection pressure could lead to a reduction in SDHI resistance frequency.…”

A molecular epidemiology study reveals the presence of identical genotypes on grapevines and ground cover weeds and the existence of separate genetic groups in a Botrytis cinerea population

“…Based on the BC‐ hch sequences, none of the isolates grouped with B . pseudocinerea clade, indicating the absence of this species in our samples, as previously reported in the same region (Vercesi et al ., 2014; Campia et al ., 2017; Toffolatti et al ., 2020). The phylogenetic analysis allowed a deeper investigation into the position of the isolates within the Botrytis genus.…”

“…B . cinerea strains were cultured on PDA and incubated at 22°C to evaluate the following parameters: mycelial growth (expressed as colony diameter in mm) between 1 and 4 days after inoculation (dai; Toffolatti et al ., 2020); colony morphology and conidia production (expressed as conidia/ml) at 10 dai (Toffolatti et al ., 2020); and vegetative incompatibility at 6 dai (Fournier et al ., 2005). Conidia were collected in 1 ml of 20% glycerol–water solution and counted at the microscope in a Kova counting grid (Hycor Biomedical Inc.).…”