Resistance to Azoxystrobin and Thiophanate-Methyl Is Widespread in spp. Isolates From the Mid-Atlantic Strawberry Fields.

Multiple species have been found to be responsible for strawberry anthracnose, and prevalence of each species seems to vary by regions and/or host tissues. In this study, a total of 200 isolates were obtained from different strawberry cultivars displaying anthracnose symptoms in the mid-Atlantic fields. Analysis of , and/or internal transcribed spacer sequences revealed four species, including , , , and . was the predominant species, representing 90% of all isolates collected. This species was found from all strawberry organs/tissues examined, whereas and were limited to the crown and fruit, respectively. Further, all isolates were screened for resistance to azoxystrobin in vitro, and all isolates were additionally screened for resistance to thiophanate-methyl. The overall frequency of resistance to azoxystrobin and thiophanate-methyl was 48 and 67%, respectively. G143A in the cytochrome gene was found in all and . isolates with high level of resistance, with EC >100 µg/ml, while F129L was found in two of the five isolates with moderate resistance, with EC values ranging from 2.6 to 7.8 µg/ml. All isolates tested were found to be less sensitive to azoxystrobin, with EC values ranging from 9.7 to 14.4 µg/ml, despite no mutations detected in the cytochrome gene. Moreover, E198A in was linked with isolates resistant to thiophanate-methyl (EC >100 µg/ml). These results revealed that resistance in spp. to primary fungicides is widespread in the mid-Atlantic strawberry fields.