Studies On Screening Of Antagonistic Biocontrol Agents And Their Mechanism Of Action Of Sclerotinia Sclerotiorum

Rapeseed is Chinese major oil crops, Sclerotinia sclerotiorum is the constant disease of the rapeseed which caused a great harm on rapeseed production. Generally result in cuts of 10% to 30%, severe 80%.In this study, producing a broad collection healthy rapeseed plant of Hubei, using agar dilution and confrontational culture isolated one strain which has a strong antagonistic effective. Its 16SrDNA sequence sequence 99% homology with Bacillus subtilis in Genbank, further to its morphological, physiological and biochemical characteristics, the strain identified as Bacillus subtilis, named for the Bacillus subtilis K-106.Bacillus subtilis K-106 has clear inhibition with Sclerotinia sclerotiorum on the PDA media. Under the microscopic, the inhibited mycelia cytoplasm uneven, granular protoplasm in the mycelium and the middle of the mycelia is enlarged. Using the suspensions of the BsK-106 dealing with the normal sclerotium, delayed the germination of sclerotia, and the number of formation sclerotia germination once again decreased of 85.71% compared to the control, while no significant inhibition of the supernatant.The rate of cell suspensions(108 cells/ml) of Bacillus subtilis K-106 inhibition of Sclerotinia sclerotiorum lesion expansion is 71.87% on detached leaves, but the suppression effect is not obvious. The field test showed that the control efficacy of Bacillus subtilis K-106 cell suspension (108 cells/ml) is 52.21% compare with the control.Using the cell suspension (108 cells/ml)of BsK-106 deal with rapeseeds, rapeseed seedling height increased by 47.3% compared with the control, and its underground parts increased 56.7%. Its aboveground and underground parts of the dry weight and wet weight is 30.2% and 12.6% higher compared with the control.Bacillus subtilis K-106 have some induction resistance to the rapeseed plants. Phenylalanine ammonialyase (PAL), superoxide dismutase (SOD), peroxidase (PO) and polyphenoase (PPO) of rapeseed plants were different responses which analyzed as indicators of rapeseed resistance to diseases after inoculated with Sclerotinia sclerotiorum and Bacillus subtilis K-106. The results showed that PO activity peaks reached at 48hr after inoculation, and PPO、PAL、SOD activity peak reached at 24hr. These four enzyme activity peak reached at different time may be related to the biocontrol strain functioning in rapeseed plant. These four enzymes activity were increased compared with the control, may be due to this reason increasing the ability of rapeseed plant resistance infection and spread of the Sclerotinia sclerotiorum.Field control experiment showed that after 104 cells/ml、106 cells/ml and 108 cells/ ml of BsK-106’s liquid culture, the control efficacy was 25.71%、41.56%and52.21%.