Link to home

Cannot retrieve the URL specified in the Content Link property. For more assistance, contact your site administrator.

Occurrence and phenotypes of pyrimethanil resistance in Penicillium expansum from apple.
R. CAIAZZO (1), Y. K. Kim (1), C. Xiao (2). (1) Washington State University, TFREC, Wenatchee, WA, U.S.A.; (2) USDA-ARS, San Joaquin Valley Agricultural Sciences Center, Parlier, CA, U.S.A.

<i>Penicillium expansum</i> is the primary cause of blue mold of apple. Pyrimethanil is a recently registered postharvest fungicide for decay control. Resistance to pyrimethanil has emerged in <i>P. expansum</i>. To monitor and characterize pyrimethanil resistance, blue mold-decayed fruit were collected in 2010 and 2011 from 5 packinghouses and the causal agents were identified to species. Isolates of <i>P. expansum</i> were tested for resistance and further classified as low resistance if conidia germinated at 0.5 µg/ml but not 10 µg/ml, moderate resistance if germinated at 10 µg/ml but not 40 µg/ml, and high resistance if germinated at 40 µg/ml. In 2010, 85% and 7% of the isolates were resistant in packinghouse A and B, respectively, where pyrimethanil had been used for 4-5 years. In 2011, either pyrimethanil or fludioxonil was used in packinghouse A, and 96% of the isolates from the fruit treated with pyrimethanil were resistant but only 4% of the isolates from the fruit treated with fludioxonil were resistant to pyrimethanil, suggesting fungicide rotation helped reduce resistance frequency. In packinghouse B, resistance frequency was reduced to 1% when fludioxonil was used instead of pyrimethnail. No resistant isolates were detected in 2010 in other 3 packinghouses where the fungicide was just recently used at a small scale, but 1% of the isolates from one of the three packinghouses in 2011 were resistant to pyrimethanil. Of the resistant isolates tested, 37-52%, 4-5% and 44-58% were phenotyped as low, moderate, and high resistance, respectively.<p><p>Keywords: Fungus, Fruits-Nuts, Apple

View Presentation