Resistance of Black Aspergilli Species from Grape Vineyards to SDHI, QoI, DMI, and Phenylpyrrole Fungicides

Fungicide applications constitute a management practice that reduces the size of fungal populations and by acting as a genetic drift factor, may affect pathogen evolution. In a previous study, we showed that the farming system influenced the population structure of the Aspergillus section Nigri species in Greek vineyards. The current study aimed to test the hypothesis that the differences in the population structure may be associated with the selection of fungicide-resistant strains within the black aspergilli populations. To achieve this, we determined the sensitivity of 102, 151, 19, and 22 for the A. uvarum, A. tubingensis, A. niger, and A. carbonarious isolates, respectively, originating either from conventionally-treated or organic vineyards to the fungicides fluxapyroxad-SDHIs, pyraclostrobin-QoIs, tebuconazole-DMIs, and fludioxonil-phenylpyrroles. The results showed widespread resistance to all four fungicides tested in the A. uvarum isolates originating mostly from conventional vineyards. In contrast, all the A. tubingensis isolates tested were sensitive to pyraclostrobin, while moderate frequencies of only lowly resistant isolates were identified for tebuconazole, fludioxonil, and fluxapyroxad. Sequencing analysis of the corresponding fungicide target encoding genes revealed the presence of H270Y, H65Q/S66P, and G143A mutations in the sdhB, sdhD, and cytb genes of A. uvarum resistant isolates, respectively. No mutations in the Cyp51A and Cyp51B genes were detected in either the A. uvarum or A. tubingensis isolates exhibiting high or low resistance levels to DMIs, suggesting that other resistance mechanisms are responsible for the observed phenotype. Our results support the initial hypothesis for the contribution of fungicide resistance in the black aspergilli population structure in conventional and organic vineyards, while this is the first report of A. uvarum resistance to SDHIs and the first documentation of H270Y or H65Q/S66P mutations in sdhB, sdhD, and of the G143A mutation in the cytb gene of this fungal species.

Automated summary

Fungicide applications can reduce fungal populations and influence pathogen evolution. This study examined the population structure of black aspergilli species in Greek vineyards and found widespread resistance to fungicides in A. uvarum isolates from conventional vineyards. However, A. tubingensis isolates showed sensitivity to pyraclostrobin. Sequencing analysis revealed mutations in the genes of resistant A. uvarum isolates, suggesting the contribution of fungicide resistance to population structure.