The Study On The Pathogenicity Differentiation And Sclerotial Formation Mechanism Of Sunflower Sclerotinia Sclerotiorum

Sunflower white rot caused by Sclerotinia sclerotiorum is the mainly disease to inhibit the sunflower production, and could cause great damage in the sunflower production all over the world. All the strains in this thesis were isolated from Wuyuan county of Bayannaoer in Innermogolia, Huinong district of Shizuishan in Ningxia and Wenquan county of Talamenggu in Xinjiang. In this study, we focused on the pathogenicity differentiation, insecticide susceptibility, the process of sclerotial formation and the inhibiting mechanism of sclerotial formation after being pretreated with cAMP and the biocontrol bacterium S-16 and CF4-51. We concluded as the followings:1. There existed the pathogenicity differentiation in all the strains from the three mentioned different regions. We also found that there was a certain percentage of strains showing weak pathogenicity, which indicated that pathogenicity of Sclerotinia sclerotiorum might descended at a certain degree.2. The result showed in insecticides susceptibility assay that there wewe a certain percentage of the strains from Xinjiang were resistant to carbendazim.3. The sclerotia of the sunflower S. sclerotiorum formed by the differentiation of a single cell instead of being gathered by mycelia.4. H2O2 played an important role in the sclerotial formation. Only when the H2O2 reached the peak, S. sclerotiorum would transform from vegetative mycelium growth stage to the initial stage of sclerotia.5. The concentration of intracellular cAMP was a key factor affecting the formation of sclerotia of S. sclerotiorum. The relative expression of Noxl and Nox2 were both inhibited when the concentration of intracellular cAMP was increasing, which result in H2O2 concentration decreased which result in the inhibition of the sclerotial formation. cAMP regulated the transformation from vegetative mycelium growth stage to the initial stage of sclerotia, and it also inhibited the maturation of sclerotia via regulating the amount of H2O2.6. S-16 which is a strain of Bacillus subtilis could make the vegetative hyphae growth abnormal and inhibit the sclerotial formation of S. sclerotiorum. The concentration of cAMP increased after being pretreated with S-16,which result from regulating Ac gene expression, however, the relative expression of Noxl and Nox2, the concentration of H2O2, and formation of the sclerotia decreased.7. CF4-51 which is a strain of Bacillus cereus strain could also make the vegetative hyphae growth of S. sclerotiorum abnormal. The activity of SOD and CAT increased via positively regulating the relative gene expression of Sod and Cat after being pretreated with CF4-51,which finally result in H2O2 decreasing and the sclerotial formation being inhibited.