Shift in sensitivity of Alternaria solani (potato early blight) to strobihirin fungicides

摘要

Forty-seven Alternaria solani isolates collected from 1998 and 2001 from various potato growing regions in the United States were assayed in vitro for sensitivity to azoxystrobin. Twenty-one A. solani isolates collected in 1998, prior to the introduction of azoxystrobin, had a mean baseline EC_(50) value of 0.0279 mu g/ml. Isolates of A. solani collected in 2001, recovered from fields displaying a lack of disease control by azoxystrobin, had a mean EC_(50) of 0.3480 mu g/mL Mean EC_(50) values forbaseline isolates to pyraclostrobin and trifloxystrobin were 0.0022 mu g/ml and 0.0060 mu g/ml respectively. In 2001, sensitivities to pyraclostrobin and trifloxystrobia shifted to mean EC_(50) values of 0.0208 mu g/ml, and 0.0140 mu g/ml respectively. In vivo assessments of sensitivity to azoxystrobin and pyraclostrobin were conducted on six isolates selected from the in vitro cross-resistance evaluations. Results from the in vivo assays were correlated to those obtained in the in vitro assays. Field studies need to be conducted to determine if the shift in sensitivity to pyraclostrobin and trifloxystrobin will result in a similar loss of disease control under commercial potato growing conditions as observed with azoxystrobin.