First report of SDHI fungicides resistant isolates of Alternaria brassicicola from broccoli in Japan.

  1. Fumihiro Nishimura
  2. Takahiro Katayama
  3. Kenichi Ikeda
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Abstract

Alternaria brassicicola is a causative agent of Alternaria sooty spot in broccoli. Isolates resistant to succinate dehydrogenase inhibitor (SDHI) fungicides were found on broccoli in Kagawa Prefecture, Japan, in 2023 and 2024. The isolates were very resistant to boscalid, penthiopyrad, pyraziflumid, and inpyrfluxam (minimum inhibitory concentration [MIC], ≥ 2700 ppm) on YBA medium, whereas the MIC value of isofetamid was 5 ppm. In fungicide control tests, only isofetamid significantly reduced disease severity compared with that in untreated controls. All 11 resistant isolates had a point mutation (A to G) in the SdhC gene, leading to an H134R substitution.

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  1. Version published to 10.21203/rs.3.rs-5894167/v1 on Research Square