Sensitivity of Fusarium oxysporum Isolates Collected from Strawberry Roots to DMI Fungicides Difenoconazole, Tebuconazole and Prochloraz

Abstract

Soil borne fungi control is particularly difficult as they survive in soil and in host plant debris for long period. Strawberry plants infected heavily by Fusarium oxysporum causing Fusarium wilt leading to serious decrease in the crop production. The application of protective fungicides extensively is the essential strategy to control the disease. However, resistant populations to the common fungicides are widely detected recently.This study aimed to detect F. oxysporum resistant populations to difenoconazole, tebuconazole and prochloraz and to find a good strategy to control the disease. In the current study, 115 F. oxysporum isolates were collected from four main strawberry-producing governorates(Beheira, Ismailia, Dakahlia and Qalubiya)in Egypt and used. The results showed that among collected isolates, 71 isolates (61.73%) were resistant to difenoconazole while 85 isolates (73.92%)were resistant to tebuconazole and 2 isolates(1.74%)were resistant to prochloraz.The EC 50 of difenoconazole, tebuconazole and prochloraz were determined for a set of sensitive and resistant isolates using the mycelial growth inhibition technique. The EC 50 mean value for difenoconazole-sensitive isolates was 0.08 µg/ml while, the EC 50 mean value for difenoconazole-resistant isolates was 1.27µg/ml. Tebuconazole's mean EC 50 concentration for susceptible isolates was 0.04µg/ml, in contrast, the mean EC 50 value for resistant isolates was 0.139µg/ml and likewise for prochloraz sensitive isolates had an average EC 50 of 0.024µg/ml, while resistant isolates had an average EC 50 of 6.97µg/ml. The combination of trifloxystrobin 25% and tebuconazole 50% tested with two concentrations 10 and 100 µg/ml showed high ability in the management of difenoconazole resistant isolates and exhibited 100% mycelial growth inhibition.