Optimization of the Culture Medium, Fermentation Process, and Effectiveness of a Biopesticide from an Iranian Bacillus thuringiensis var. tenebrionis (BN۲)

The local strain of B. thuringiensis var. tenebrionis-BN۲ (Btt-BN۲) was used to control the alfalfa weevil. Experimental design using Response Surface Methodology (RSM) was applied for the optimization of the culture medium and fermentation parameters in order to achieve a high level of Colony-Forming Unit (CFU) (spore mL−۱). The parameters including the amount of carbon and nitrogen sources at three levels were investigated with CFU (spore mL−۱) response for two sets of experiments. The obtained results showed that the maximum CFU (spore mL−۱) for the minimum concentration of oat (۲ g L-۱), the minimum concentration of corn steep liquor (۱۰ g L-۱), and the maximum concentration of sugarcane molasses (۱۰ g L-۱) were equivalent to ۱.۴×۱۰۱۳ spore mL-۱. Optimum fermentation parameters to obtain the highest value of CFU (spore mL−۱) were determined as a maximum level of pH of eight and a medium level of temperature (۲۸۰C). Amazingly, optimum conditions enhanced the CFU value to ۸.۰۶× ۱۰۱۳ spore mL-۱, which is very significant in the Btt research. Finally, the bioassay analysis of Btt in a single system and binary system (combination of two insecticides; Matrine® and Abamectin®) at different concentrations illustrated ۸۳% of mortality efficiency (۳ ppm of Btt and ۰.۵ ppm Matrine) on the ۳rd day of treatment and ۱۰۰% efficiency almost for all combination of Btt with Matrine and/or Abamectin after the ۷th day. The bioassay results showed promising environmentally friendly mortality efficiency compared to the current chemical treatments.

کلیدواژه ها:

Alfalfa weevil ، Biological control ، Fermentation parameters ، Integrated Pest Management ، Mortality.