Assessing boscalid efficacy and resistance in large-spored Alternaria pathogens of potato and tomato crops

The resistance of large-spored Alternaria species in the Porri section to boscalid was evaluated through laboratory assays. Most isolates had EC50 values above 100 μg/mL, indicating widespread fungicide resistance. Only isolates of A. solani demonstrated sensitivity, with EC50 values below 7 μg/mL. Isolates of A. linariae, A. protenta and A. alternariacida were resistant. A moderate level of resistance to the fungicide was detected in A. grandis (mean EC50 = 76, 8 μg/mL). Although the resistance levels varied among strains, sampling location did not appear to be a significant factor. One of the primary targets of boscalid within fungal cells is the succinate dehydrogenase (SDH) enzyme complex, which consists of several subunits. Mutations in these genes have been identified as a key mechanism of boscalid resistance in various fungal pathogens. Our study revealed the absence of H134R and H278Y mutations within the SdhB gene among the Alternaria isolates. We further analysed the sequences of Sdh gene subunits B, C, and D in isolates originating from potato, including A. alternariacida, A. grandis, A. linariae, A. protenta, and A. solani. This analysis identified several single nucleotide polymorphisms (SNPs) that effectively distinguished these isolates from tomato-derived A. linariae ones. © The Author(s), under exclusive licence to Deutsche Phytomedizinische Gesellschaft 2025.