Fungicide resistance profiling in Botrytis cinerea populations from blueberries in California and Washington and their impact on control of gray mold

Authors: Saito, Seiya; MICHAILIDES, T - University Of California; Xiao, Chang-Lin

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/22/2016
Publication Date: 9/26/2016
Citation: Saito, S., Michailides, T.J., Xiao, C. 2016. Fungicide resistance profiling in Botrytis cinerea populations from blueberries in California and Washington and their impact on control of gray mold. Plant Disease. 100(10):2087-2093. doi: 10.1094/PDIS-02-16-0229-RE.

Interpretive Summary: Gray mold caused by the fungus Botrytis cinerea is a major postharvest disease of blueberries grown in the Central Valley of California (CA) and western Washington State (WA). Control of gray mold has largely relied on the use of fungicides, but fungicide resistance in B. cinerea can result in the failure of disease control. In this study, we examined sensitivities to boscalid, cyprodinil, fenhexamid, fludioxonil, and pyraclostrobin, representing five different fungicide classes, in 249 and 106 isolates of B. cinerea recovered from decayed blueberry fruit in CA and WA, respectively. In CA and WA, respectively, 66 and 49% of the isolates were resistant to boscalid; 20 and 29% were moderately resistant to cyprodinil; 29 and 29% were resistant to fenhexamid; and 66 and 55% were resistant to pyraclostrobin. All isolates from CA were sensitive to fludioxonil, while 70% of the isolates from WA showed reduced sensitivity to fludioxonil. In CA, 26 and 30% of the isolates were resistant to two and three classes of fungicides, respectively. In WA, 31, 14, 16, and 9% of the isolates were resistant to two, three, four, and five classes of fungicides, respectively. On detached blueberry fruit inoculated with 11 isolates exhibiting different fungicide-resistant phenotypes, most fungicides failed to control gray mold on fruit inoculated with respective resistant phenotypes, but the mixture of cyprodinil and fludioxonil was effective against all fungicide-resistant phenotypes tested. Our findings would be useful in designing and implementing fungicide resistance management spray programs for control of gray mold in blueberry.

Technical Abstract: Gray mold caused by Botrytis cinerea is a major postharvest disease of blueberries grown in the Central Valley of California (CA) and western Washington State (WA). Sensitivities to boscalid, cyprodinil, fenhexamid, fludioxonil, and pyraclostrobin, representing five different fungicide classes, were examined for 249 and 106 B. cinerea isolates recovered from decayed blueberry fruit in CA and WA, respectively. Seven and 17 fungicide-resistant phenotypes were detected; 66 and 49% of the isolates were resistant to boscalid; 20 and 29% were moderately resistant to cyprodinil; 29 and 29% were resistant to fenhexamid; and 66 and 55% were resistant to pyraclostrobin in CA and WA, respectively. All isolates from CA were sensitive to fludioxonil, while 70% of the isolates from WA showed reduced sensitivity to fludioxonil. In CA, 26 and 30% of the isolates were resistant to two and three classes of fungicides, respectively. In WA, 31, 14, 16, and 9% of the isolates were resistant to two, three, four, and five classes of fungicides, respectively. Inherent risk of the development of resistance to QoI fungicides was assessed by detecting the presence of the Bcbi-143/144 intron in cytb gene. The intron was detected in 11.8% and 40% of the isolates in CA and WA, respectively, suggesting that the risk of QoI resistance is higher in CA than in WA. On detached blueberry fruit inoculated with 11 isolates exhibiting different fungicide-resistant phenotypes, most fungicides failed to control gray mold on fruit inoculated with respective resistant phenotypes, but the mixture of cyprodinil and fludioxonil was effective against all fungicide-resistant phenotypes tested. Our findings would be useful in designing and implementing fungicide resistance management spray programs for control of gray mold in blueberry.