Prevalence and characterization of iprodione and fludioxonil resistance in Botrytis cinerea isolates from small fruits in the southeastern U.S.
A. GRABKE (1), X. Li (1), D. Fernández-Ortuño (1), A. Amiri (2), N. A. Peres (2), G. Schnabel (1). (1) Clemson University, Clemson, SC, U.S.A.; (2) University of Florida, Wimauma, FL, U.S.A.
The control of gray mold in small fruits is largely dependent on the application of fungicides, including iprodione and fludioxonil. A total of 516 single-spore isolates of <i>Botrytis cinerea</i> were collected from commercial strawberry fields in Florida, North Carolina, and South Carolina and blackberry fields from the Carolinas to determine occurrence and prevalence of resistance. Based on a spore-germination assay, most isolates were either low resistant (LR) or sensitive (S) to iprodione. Five isolates (1%) highly resistant (HR) to iprodione were found in blackberry fields and isolates with moderate resistance (MR) were found at low frequencies in strawberry fields. Detached fruit assays indicated that field rates of Rovral (a.i. iprodione) controlled the S and LR but not the MR and HR isolates. Moderate resistance to iprodione was associated with both the Q369P and N373S mutations in the Class III Histidine-Kinase Bos1. The I365S and I365N mutations were present in LR and HR isolates indicating that these mutations were not responsible for the HR phenotype. Of the five HR isolates to iprodione, two were S, one was MR, and two were HR to fludioxonil. The presence of the R632I mutation in the <i>mrr1</i> transcriptional regulator gene and overexpression of the <i>atrB</i> gene indicated MDR1 activity in the two isolates highly resistant to fludioxonil.
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