Research On Biological Activity Of Strobilurin Fungicide Pyraclostrobin Against Sclerotinia Sclerotiorum

Sclerotinia sclerotiorum is a pathogenic fungus infecting a variety of hosts, including oilseed rape and other oil crops. The control of S. sclerotiorum is still relied heavily on fungicides. Strobilurin fungicides have been widely used in the control of many pathogenic fungi, but in China most of Strobilurin fungicides have not yet been used to control S. sclerotiorum. To provide advices for using pyraclostrobin to control S.sclerotiorum, biological activity of pyraclostrobin toward S. sclerotiorum were assessed.Effects of methanol, ethanol, acetone and dimethyl sulfoxide on S. sclerotiorum and biological activity of pyraclostrobin were evaluated by mycelium growth rate method,and results showed that effect of the 4 solvents on biological activity of pyraclostrobin toward S. sclerotiorum was significant if the concentrations of the 4 solvents were higher than 0.5% by volume in potato dextrose agar(PDA). We suggested that solvent concentration should not exceed 0.5% in PDA to avoid miscalculation of biological activity of fungicides. Baseline sensitivity of pyraclostrobin to S. sclerotiorum from China was established, the mean EC50 of sensitivity baseline was 0.1027 μg/m L±0.0916(SD)and individual EC50 values of pyraclostrobin were from 0.0124 to 0.6324 μg/m L. There was no cross-resistance between pyraclostrobin and carbendazim or dimethachlon.Preventive efficacy of pyraclostrobin against S. sclerotiorum was higher than curative efficacy in pot experiments, so pyraclostrobin should be used as a protectant.Salicylhydroxamic acid(SHAM) at 40 μg/m L can inhibit the growth of hyphae of S.sclerotiorum by over 30%. SHAM at 40 μg/m L can significantly potentiate in vitro toxicity of pyraclostrobin toward S. sclerotiorum. Mixture of SHAM at 20 μg/m L and pyraclostrobin at 10 μg/m L showed synergism with respect to the control efficacy in port experiments. This implied that SHAM may inhibit other biochemical enzymes beside the alternative pathway of respiration in S. sclerotiorum. Therefore, SHAM may not be added in artificial medium in assessing in vitro toxicity of pyraclostrobin against S.sclerotiorum.Pyraclostrobin could inhibit hypha growth and sclerotia production of S.sclerotiorum. Pyraclostrobin at 0.1 and 1 μg/m L could reduce sclerotia production by18% and 34%, respectively. Pyraclostrobin at 0.01, 0.1 and 1 μg/m L had no significanteffect on permeability of cell membrane and production of oxalic acid of S. sclerotiorum.However, protein synthesis was significantly reduced by pyraclostrobin at 1 μg/m L.