Sensitivity of Peronophythora litchii at different development stages to four QoI fungicides

Litchi downy blight, caused by Peronophythora litchii, is one of the most important diseases of litchi. Sensitivities of P. litchii to four QoI fungicides including enestroburin, SYP-1620, SYP-2815 and ZJ0712, were tested in vitro at different development stages. The results showed that all four QoI fungicides had strong inhibitory activity on mycelial growth and sporangium production of P. litchii, with EC50 values ranging from 0.197 0 to 1.257 9 μg/mL and from 0.212 7 to 0.816 0 μg/mL, respectively. The release of zoospore from sporangium was less inhibited by these fungicides, with EC50 values ranging from 4.144 8 to 7.425 3 μg/mL, while the rupture of zoospore was accelerated and the information of cystospore was inhibited when exposed to certain concentrations of these fungicides. All four QoI fungicides showed much strong inhibitory activity on the germination of sporangium and cystospore, with EC50 values ranging from 0.046 5 to 0.342 4 μg/mL and from 0.036 5 to 0.187 7 μg/mL, respectively.