Evaluation of alternative culture media for on-farm multiplication of Bacillus thuringiensis-based bioinputs for use in agriculture

Abstract

The number of bio-input registrations in Brazil has been growing, as these inputs have a lower environmental impact and lower costs, as well as being a sustainable alternative to the application of synthetic products. Among bio-inputs of microbial origin, bacteria of the Bacillus genus are widely applied in agriculture, with Bacillus thuringiensis (Bt) being the most widely used bacterium globally in pest control. However, in the production of bio-inputs of microbiological origin, the culture media are responsible for a large part of the production cost. This work therefore aimed to evaluate alternative culture media for Bt cultivars. Bacterial sporulation was quantified in seven liquid culture media, with sugarcane molasses, glucose, sucrose or starch as the main carbon source and soybean meal and yeast extract as the nitrogen source. Cultivation in a solid medium composed of rice and water was also evaluated. Finally, the medium containing sugar cane molasses and yeast extract was evaluated for its preparation in the presence of active chlorine. At the end of the tests, it was concluded that all the media tested were effective for the growth of Bt, with spore counts in the order of 10⁶ UFC mL^-1 to 10⁹ UFC mL^-1, without contamination by Gram-negative bacteria, making them viable options for the on-farm multiplication of microorganisms for agriculture as they use low-cost and easily accessible inputs.

Key words: biological control; biopesticide; submerged fermentation.