Sensitivity of Monilinia fructicola isolates to azoxystrobin.

In this study, the sensitivities of Monilinia fructicola isolates collected from different areas in north China to salicylhydroxamic acid (SHAM) and azoxystrobin were investigated by testing the relative spore germination rate and the relative mycelia growth rate on media containing these chemicals, respectively. Therefore , proper SHAM concentration was provided to test the sensitivity of M. fructicola to azoxystrobin in vitro and a basis was set up to monitor the presence of fungicide resistance in the field. The results showed that when SHAM concentration is 60 mg·L-1, the inhibition rate of this chemical to the growth of mycelium of 43 isolates of M. fructicola ranged from -3.09% to 52.93%, while spore germination of 32 tested isolates was not obviously affected . The results suggested that this concentration was suitable to be used in the test of the inhibition effect of azoxystrobin on Monilinia fructicola using the spore germination method but not using the mycelial growth rate. The result also showed that the frequency distribution of the EC50 values of azoxystrobin to 55 isolates from different areas of China was normal with one peak, ranging from 0.075 mg·L-1 to 0.390 mg·L-1, with a mean value of (0.210±0.072) mg·L-1, which could be used as a baseline.