Antagonistic evaluation of Bacillus subtilis isolated from arid zones of Sonora against Fusarium oxysporum in watermelon
Keywords:
Bacillus subtilis, Fusarium spp., Biological control, In vitro antagonism, Watermelon; Sonora.Abstract
The growing demand for organic products is driving the search for sustainable alternatives that reduce the use of agrochemicals and protect environmental health. In this context, biocontrol using rhizospheric microorganisms is emerging as a key solution, with the genus Bacillus standing out for its abundance and metabolic versatility. In particular, Bacillus subtilis has the ability to produce antimicrobial metabolites that effectively inhibit various phytopathogens, in addition to acting as a potent promoter of plant growth. However, it is essential to evaluate these interactions beyond the laboratory, as the mechanisms of action can vary when faced with the complexity of real-world agricultural ecosystems. The aim of this study was to evaluate the in vitro antagonistic effect of native and commercial Bacillus subtilis strains against Fusarium oxysporum, the causal agent of vascular wilt in watermelon. Four native Bacillus subtilis strains were isolated from rhizospheric soils associated with palo verde trees in different locations of Sonora, Mexico. Likewise, Fusarium oxysporum was isolated from symptomatic watermelon plants and morphologically characterized. The antagonism assay was conducted through dual culture on PDA, assessing mycelial growth as an indicator of inhibition. Results showed that all native strains significantly reduced Fusarium oxysporum mycelial growth, with values ranging from 2.5 to 3.3 cm compared to the control (5.8 cm). Bacillus subtilis strain 02 exhibited the highest antagonistic capacity, even outperforming the commercial biocontrol strain BsUV. Images from the assay revealed clear inhibition halos, mycelial deformation, and reduced fungal density, visually confirming the antagonistic effect. These findings demonstrate the potential of native Bacillus subtilis strains as biological control agents for managing Fusarium oxysporum in watermelon production. Further studies under greenhouse and field conditions are recommended to validate their efficacy in real-world production environments. Overall, this work contributes to the development of sustainable strategies for plant disease management in agricultural systems of northwestern Mexico.
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