Resistance of Sclerotinia homoeocarpa Field Isolates to Succinate Dehydrogenase Inhibitor Fungicides

摘要

Sclerotinia homoeocarpa isolates were collected from golf courses in Japan and the United States (2016-2017). Japan isolates were collected during a monitoring study and the U.S. isolates were collected due to field failure. Five succinate dehydrogenase inhibitor (SDHI) active ingredients (boscalid, fluopyram, fluxapyroxad, isofetamid, and penthio-pyrad) were examined using in vitro sensitivity assays to determine cross-resistance. Sequence analysis revealed a point mutation leading to an amino acidsubstitution (H267Y) and a silent mutation (CTT to CTC) at codon 181 in the SdhB subunit gene. Isolates with the B-H267Y (n = 10) mutation were resistant to boscalid and penthiopyradand had increased sensitivity to fluopyram. SdhB silent mutation 181 C>T isolates (n = 2) were resistant to boscalid, isofetamid, and penthiopyrad. Sequence analysis revealed 3 mutations leading to an amino acid substitution (G91R, n = 5; G150R, n = 1; G159W, n= 1) in the SdhC subunit gene. Isolates harboring the SdhC (G91R or G150R) mutations were resistant to boscalid, fluxapyroxad, isofetamid, and penthiopyrad. A genetic transformation system was used to generate mutants from a SDHI sensitive isolateto confirm the B-H267Y and C-G91R mutations were direct determinants of SDHI resistance and associated with in vitro sensitivity assay results.