Abstract: The activity of azoxystrobin inhibiting mycelial growth of Sclerotinia sclerotiorum was tested by mycelial growth rate method and the effect of azoxystrobin on the sclerotinia yield and respiration in mycelial growth of S.sclerotiorum was assessed.The results showed that azoxystrobin strongly inhibited the mycelial growth,and 1.0 μg/mL azoxystrobin could inhibit sclerotinia production obviously.Synergistic interaction against S.sclerotiorum existed between salicylhydroxamic acid (SHAM),a specific inhibitor of alternative oxidase,and azoxystrobin.The synergistic ratio ranges from 3.27 to 14.13.The dose-response curves of azoxystrobin inhibiting mycelial growth were almost parallel to that of oxygen consumption rate of the fungus within 48 h.However,higher oxygen consumption rate in mycelia than the untreated was found 48 hours after treated with azoxytrobin,and the mycelial growth did not increase.It suggested that some urgent reaction of mycelia occurred in response to the inhibition of azoxystrobin in S.sclerotiorum after 48 h.SHAM did not show the inhibitory activity against the mycelial respiration of S.sclerotiorum within 1 h until the mycelia was treated with azoxystrobin after 1 h,indicating that the alternative oxidase pathway could be induced when mitochondrial electron transferring in cyt bc1 complex was prevented by azoxystrobin.