Genetic diversity and pathogenicity of the grey mould fungus Botrytis

Resumen de la conferencia. Genetic diversity and pathogenicity of the grey mould fungus Botrytis Botrytis spp., causes preand postharvest decay on strawberry crops. Botrytis spp. isolates from several German strawberry-growing fields, which received several fungicide treatments against Botrytis per season, were analyzed to determine their sensitivity against botryticides. Fungicide resistance was commonly observed in B. cinerea, with many isolates possessing resistance to multiple fungicides. A stronger variant of the previously described multidrug resistance (MDR) phenotype MDR1, called MDR1h, was found to be widely distributed, conferring increased partial resistance to two important botryticides, cyprodinil and fludioxonil. A 3-bp deletion mutation in a transcription factor- encoding gene, mrr1, was found to be correlated with MDR1h. All MDR1h isolates and the majority of isolates with resistance to multiple fungicides were found to be genetically distinct. Multiple-gene sequencing confirmed that they belong to a novel clade, called Botrytis group S. Isolates of Botrytis group S genotypes were found to be widespread in all German strawberry-growing regions but almost absent from vineyards. On the other hand, it was investigated the presence and fungicide sensitivity of B. pseudocinerea, which has been found previously to occur together with B. cinerea in low abundance in vineyards and strawberry fields. Abundance of B. pseudocinerea was often negatively correlated with fungicide treatments. On cultivated strawberries, it was frequently found in spring but was largely displaced by B. cinerea following fungicide applications. B. pseudocinerea almost never developed resistance to any fungicide even though resistance mutations occurred at similar frequencies in both species under laboratory conditions. Moreover, during the surveys carried out in the strawberry fields in Germany, some Botrytis isolates differed from B. cinerea and B. pseudocinerea in diagnostic PCR markers and growth appearance. Phylogenetic analyses showed these strains to belong to an undescribed species in Botrytis clade 2, named Botrytis fragariae sp. nov. Isolates of B. fragariae were detected in strawberry fields throughout Germany, sometimes at similar frequencies as B. cinerea. Various fungicide resistance patterns were observed in B. fragariae populations. Many B. fragariae islates showed also resistance to one or several chemical classes of fungicides, and an efflux-based multidrug resistance (MDR1) phenotype previously described for B. cinerea. Resistance-related mutations in B. fragariae were identical or similar to those of B. cinerea for carbendazim (E198A mutation in tubA), azoxystrobin (G143A in cytB), iprodione (G367A+V368F in bos1) and MDR1 (gain-of-function mutations in the transcription factor mrr1 gene, and overexpression of the drug efflux transporter gene atrB). The widespread occurrence of B. fragariae indicates that this species is adapted to fungicidetreated strawberry fields and may be of local importance as a gray mold pathogen alongside B. cinerea. Therefore, the sensitivity of the Botrytis population to botryticides should be frequently monitored in order to report shifts in sensitivities. The rotation and mixture with other site-specific or multi-site fungicides, such as thiram and captan, should be included to improve disease management in B. cinerea and B. fragariae populations.