Optimization Of Biocontrol Bacterial Strain CAB-1 Against Cucumber Powdery Mildew And Grey Mold

Strain CAB-1 is a potential bacterium isolated and stored by Plant Disease Biocontrol Research Lab, Plant Protection Institute, Hebei Academy of Agricultural and Forestry Sciences. Field tests showed that strain CAB-1 effectively controled vegetable diseases, such as cucumber powdery mildew, cucumber grey mold, tomato grey mold and tomato leaf mold.The powdery mildew was identified as Sphaerotheca fulginea by morphological characteristics in our study. Bioassay system was established to test the control activity of strain CAB-1 against cucumber powdery mildew under greenhouse condition with temperature of 25-34℃and humidity of 45%-75%. The suspension of S. fulginea (3×105--5×105 conidia / mL) was sprayed on cucumber plant 24h before spaying of strain CAB-1 suspensions from 16℃different media., The control efficacy of strain CAB-1 against the disease was investigated after 7d treatment. Results showed that control efficacy of the fermentation suspension from No.2 medium was higher than that of the other media. The fermentation condition of strain CAB-1 from No.2 medium was optimized in the shake flasks, the result showed that the optimum culture condition was at 25℃with initial pH 7, 2% inoculum volume, 100 ml medium in 250 ml flask and rotation speed of 180r/min.Inhibitation of strain CAB-1 against Botrytic cinerea was carried out on the modified PDA media amended with CAB-1 suspension from the 16 different fermentation media. The result indicated that the No.4 medium was the optimum medium for producing antifungal substance against the mycelial growth of B. cinerea. The No.4 medium fermentation condition of strain CAB-1 were optimized through single factor experment in the shake flask.The result showed that the optimum culture condition of strain CAB-1 in No.4 medium was at 31℃for culturing 48 h. The activity of the antifungal substance from strain CAB-1 maintained stable by heated at 60℃. The antifungal activity kept stable after ultrasonic for 20 min, and then decreased after 30min. The antifungal activity of strain CAB-1 was also stable under UV ray for 20, 30 and 40 min. The antifungal activity of strain CAB-1 decreased significantly after UV ray treatment for 50min. The result still convinced that the antifungal activity maintained the highest at pH 6, 10 and 11.