Studies On Spore Heat Resistance And Resistance Risk Of Biocontrol Bacterial Strain BAB-1

Bacillus subtilis BAB-1acted as the effective component of biological fungicidecould effectively control tomato gray mould. The short shelf life and resistance riskcould be two major problems in the commercial field application of biological additives.Based on commercial requests, the studies were conducted to find strategies tomanaging these two problems.In order to enhance the heat resistance of spores from strain BAB-1, the effects ofadditive A on spore heat resistance were evaluated by adding additive A into the brothbefore and after fermentation. The results showed that additive A at the concentrationof0.2%could significantly enhanced spore heat resistance whenever it was added.The addition of additive A to the broth could shorten the sporulation time and increasethe sporulation rate. The action mode of additive A with the spores was alsopreliminary studied, the results indirectly confirmed that additive A could penetrate intothe spores and result in enhancing of spore heat resistance. The optimal actiontemperature was above65℃.In order to analysis of the resistance risk of Botrytis cinerea to strain BAB-1, theresistances of the pathogen to the fermentation supernatant, crude lipopeptides andfengycin from strain BAB-1were evaluated, respectively. The resistance mutants wereinduced by subculturing the sensitive strain of B. cinerea on the media containing thesupernatant, crude lipopeptides and fengycin, respectively. The result showed that theresistance level of B. cinerea to the supernatant was1.42times higher than the wildstrain after9generation acclimatization and EC50values changed from0.043mL/L to0.061mL/L. No significant resistance mutant was induced against the supernatant. After9generation acclimatization, the resistance level of B. cinerea to the crude lipopeptideswas0.97times higher and EC50values changed from0.330mg/L to0.321mg/L, noresistance mutant was obtained. However, the resistance level to fengycin was38.39times higher after9generation acclimatization, the EC50values increased from2.922mg/L to112.186mg/L. The resistant mutant was obtained. In order to manage thepathogen resistance,20mg/L surfactin was added into fengycin suspension. The resistance level of B. cinerea to fengycin decreased significantly, and EC50valuesdecreased from112.186mg/L to7.77mg/L.