Sensitivity of Fusarium oxsporum Isolates Collected from Strawberry Rots to QoI Fungicides Azoxystrobin and Trifloxystrobin

Egypt is among the top five countries in strawberry production and leads the Arab world in both production and exportation. More than five thousand hectares of land in Egypt are used to grow strawberries. Fusarium wilt in strawberries caused by Fusarium oxysporum can severely decrease production. The essential strategy to control the disease is the application of protective fungicides. Recently, the fungicides commonly used to control the disease lost their efficiency due to the emergency of resistant populations. The current study aims to detect resistance frequency to QoI fungicides azoxystrobin and trifloxystrobin in addition to finding an appropriate control strategy. 113 F. oxysporum isolates were collected from four main strawberry-producing governorates (Beheira, Ismailia, Dakahlia and Qalyubia) and subjected to bioassay assessment. The results showed that among 113 isolates collected, only 42 (37.2%) isolates were resistant to azoxystrobin while 36 (31.9%) isolates were resistant to trifloxystrobin. EC50 of azoxystrobin and trifloxystrobin were determined for a set of sensitive and resistant isolates using the mycelial growth inhibition technique. The EC50 mean value for azoxystrobin-sensitive isolates was 0.0209 µg/ml while, the EC50 mean value for azoxystrobin-resistant isolates was 0.4544 µg/ml. For trifloxystrobin, the EC50 mean value for sensitive isolates was 0.0174 µg/ml, while the EC50 mean value for resistant isolates was 0.2232 µg/ml. The combination of tebuconazole 50% and trifloxystrobin 25% tested with two concentrations 10 and 100 µg/ml showed high ability in the management of azoxystrobin and trifloxystrobin-resistant isolates and exhibited 100% mycelial growth inhibition.