APS Homepage

POSTERS: Fungicide and antibiotic resistance

Species identification and fungicide resistance profiling of Botrytis isolates from Maryland vineyards
Scott Cosseboom - University of Maryland. Mengjun Hu- University of Maryland

Botrytis bunch rot of grapes, caused by Botrytis spp., is a significant disease in the Mid-Atlantic United States and the pathogen is notorious for acquiring resistance to multiple chemical classes of fungicides. In the fall of 2018, 92 Botrytis isolates were collected from symptomatic grape berries in six Maryland vineyards. A subset of 20 isolates were identified to be Botrytis cinerea based on sequences of the glyceraldehyde-3-phosphate dehydrogenase (G3PDH) gene. In addition, all 92 isolates were subjected to a resistance profile kit described previously. Frequencies of resistance to the following fungicides were: 0% to adepidyn, fludioxonil, and isofetamid, 1% to benzovindiflupyr, 2% to penthiopyrad, 13% to boscalid, 27% to iprodione, 41% to fenhexamid, 66% to cyprodinil, 84% to thiophanate-methyl, and 98% to pyraclostrobin. These isolates were resistant to one (4%), two (15%), three (35%), four (38%), or five (8%) different chemical classes. Mutations were found in the following target genes of resistant isolates: I365N and I365S in bos1, E198A in ?-tubulin, G143A in cytB, F412I/S in erg27, and H272R/Y and P225F in sdhB. Resistance frequencies were largely consistent among the six vineyards for all fungicides except for cyprodinil, fenhexamid, and iprodione, presumably due to diverse spray programs. Use of phenylpyrroles and newer succinate dehydrogenase inhibitors needs to be limited to maintain their efficacy.