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Evaluation of the biocontrol capacity of Bacillus thuringiensis isolated from Capsicum sp., crops against Fusarium oxysporum
Introduction. The production of chili peppers in Colombia exceeds 100,000 tons per year; however, the yield of Capsicum spp. has decreased due to the influence of pests and di seases caused by phytopathogenic fungi, leading to losses of over 40%. Chemical control, although widely used, poses significant risks to both the environment and human health, in addition to generating resistance in microorganisms. The use of Bacillus thuringiensis (Bt) emerges as an effective biological alternative. Objective. To evaluate the biocontrol capacity of Bacillus thuringiensis isolated from soils cultivated with Capsicum sp. plants in the municipality of San Diego, Cesar, against the phytopathogenic fungus Fusarium oxysporum.
Methodology. This project was carried out in three phases. In Phase I, soil samples from chili crops were collected and processed to isolate Bacillus thuringiensis co lonies. In Phase II, the isolates were characterized through macroscopic, microscopic, and biochemical analyses, as well as molecular identification using mass spectrometry (MAL DI-TOF). In Phase III, the antagonistic activity of Bacillus thuringiensis isolates against Fusarium oxysporum was evaluated by measuring the inhibition halos of fungal growth. Statistical analyses were applied to assess significant differences between isolates.
Results. Bacillus thuringiensis isolates were successfully selected from soil samples cultivated with Capsicum sp., using effective enrichment isolation techniques, which outperformed the use of sodium acetate. The isolates exhibited typical Bt characteristics, such as Gram-positive bacilli with subterminal spores and Cry protein crystals, confirmed through scanning elec tron microscopy (SEM) observations. Biochemical tests verified their ability to ferment glucose and sucrose, as well as their production of proteases and amylases. Antagonism tests revealed a variable capacity to inhibit Fusarium oxysporum, with isolates SAN 001 and SAN 004 standing out.
