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Fungicide resistance profiles of blossom-derived Botrytis isolates from strawberry fields
M. J. HU (1), D. Fernández-Ortuño (2), P. K. Bryson (1), G. Schnabel (1). (1) School of Agricultural, Forest & Environmental Sciences, Clemson University, Clemson, SC, U.S.A.; (2) Instituto de Hortofruticultura Subtropical y Mediterránea "La Mayora"-Universidad de Málaga-Consejo Superior de Investigaciones Científicas (IHSM-UMA

From 2012 to 2014, a total of 1484 <i>Botrytis</i> isolates collected from strawberry blossoms from ten states in the United States were subject to the fungicide sensitivity assays described in our previous publication. The overall frequencies of resistant isolates collected in 2012 for thiophanate-methyl, pyraclostrobin, fenhexamid, cyprodinil, iprodione, boscalid, and fludioxonil were 68.6, 20.5, 10.5, 12.7, 2.3, 13.2, and 0.5%, respectively. Frequencies of isolates collected in 2013 were 88.2, 51.8, 13.8, 19.1, 1.8, 9.8, and 0.9%, respectively. Frequencies of isolates collected in 2014 were 86.6, 70.7, 30.9, 28.7, 24.0, 7.4, and 2.8%, respectively. Resistance to thiophanate-methyl was found in virtually every location in all three years, whereas resistance to fludioxonil was rarely found. Frequencies of isolates with resistance to pyraclostrobin, fenhexamid, cyprodinil, and fludioxonil were increasing, whereas resistance frequency of isolates for boscalid was decreasing during 2012 to 2014. Resistant isolates were resistant to either one (1SR; 41.4%), two (2SR; 16.4%), three (3SR; 8.2%), four (4SR; 6.8%), five (5SR; 0.5%), or six (6SR; 0) in 2012. In 2013, this distribution was 37.1, 24.2, 16.0, 9.6, 2.4, and 0.2% whilst it was 17.2, 23.8, 19.4, 15.5, 8.7, and 2.1% in 2014. The data showed a shift from 1SR to 6SR in the frequencies of multifungicide resistant isolates from 2012 to 2014, indicating an increase of multifungicide resistance.

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