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POSTERS: Fungicide and antibiotic resistance

Resistance to thiophanate-methyl in Botrytis spp. from greenhouse crops in Kansas
Chandler Day - First Author. Megan Kennelly- Kansas State University

Gray mold, caused by Botrytis cinerea and other Botrytis species, is a cosmopolitan disease affecting diverse plants, including greenhouse crops. Greenhouse growers use routine fungicide applications as part of gray mold management, and resistance to several fungicide classes has been reported. Our objective was to determine sensitivity to methyl benzimidazole carbamate (MBC) fungicides in Kansas isolates. In 2018, 34 single-spore isolates were cultured from greenhouse crops at 14 sites in Kansas. Isolates were tested on 9 cm diameter 1% Malt Extract Agar plates amended with 100 ?g/ml thiophanate-methyl. Each isolate was plated on three fungicide-amended and three unamended control plates. The plates were incubated for 5 days in the dark at 22° C. Two colony diameters were measured, excluding the 5mm starter plug, and relative mycelial growth (RMG) was calculated as the average diameter on fungicide-amended media divided by the average diameter on the control times 100. The entire experiment was conducted twice. Of the 34 isolates, 27 exhibited resistance, with RMG ?75%. Two isolates were highly sensitive, with RMG ?5%. Five isolates exhibited intermediate RMG values. Results of the study indicate that resistance to MBC fungicides is common in gray mold in Kansas greenhouses. Ongoing and future studies will include additional isolates and sequence-based identification of the Botrytis isolates.