Inhibitory Effect of Azoxystrobin on Alternaria solani

Inhibitory activity of azoxystrobin against mycelial growth and conidia germination of Alternaria solani was tested and the effect of azoxystrobin on respiration in mycelial growth of A.solani was assessed by testing the oxygen consumption.The results showed that the inhibitory activity of azoxystrobin against conidial germination was much stronger than that against mycelial growth.The dose-response curves of azoxystrobin inhibiting mycelial growth and oxygen consumption of the fungus were parallel to each other.However,oxygen consumption restored to the normal level of control after 5~7 hours treatment with azoxystrobin,and the restored oxygen consumption was insensitive to azoxystrobin.By contrast,azoxystrobin could inhibit mycelial growth of A.solani all the times.Therefore, it is more appropriate to determine sensitivity of A.solani to azoxystrobin and monitor the resistance by conidial germination test than by mycelial growth.Salicylhydroxamic acid (SHAM) could strengthen the inhibitory effect of azoxystrobin against mycelial growth and conidia germination of A.solani and the mean synergistic ratio for mycelial growth was 7.24.As treatment time went on,the respiration inhibition on the mycelia decreased,while the mycelial growth was still inhibited strongly. The results showed that the sensitivity decrease of mycelial respiration to azoxystrobin was not caused by induction of alternative respiration or degradation of the fungicide in medium.