Christiana dos Santos Azevedo

Universidade Estadual De Santa Cruz, Brazil

Abstract Title:Potential of trichoderma harzianum, bacillus pumilus and azospirillum brasiliense in the biocontrol of fusarium oxysporum: mycelial inhibition and effects of volatile and non-volatile compounds

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Fusarium wilt, caused by Fusarium oxysporum, is a destructive vascular disease that severely affects several crops and requires sustainable management strategies. This study evaluated the in vitro antagonistic activity of commercial products based on Trichoderma harzianum, Bacillus pumilus, and Azospirillum brasiliense against F. oxysporum f. sp. passiflorae (FOP) and F. oxysporum f. sp. cubense (FOC). Direct and indirect confrontation assays were performed, including the evaluation of soluble metabolites and volatile organic compounds. For non-volatile compounds, the microorganisms were grown in liquid medium under agitation, followed by centrifugation and filtration to obtain cell-free extracts, which were applied to culture medium containing a mycelial disk of Fusarium placed at the center of the plate. For volatile compounds, the sealed plate method was used, allowing only gaseous interaction between the antagonist and the pathogen. Data were subjected to ANOVA and Tukey’s test using R software and the ExpDes.pt package. The results showed significant inhibition of mycelial growth and marked morphological changes in the pathogen, including alterations in colony color, reduced mycelial density, irregular colony growth, and hyphal deformation. Volatile compounds such as 1-octen-3-ol, 3-octanol, furanones, aromatic aldehydes, and ethyl acetate, as well as lipopeptides such as fengycin, surfactin, and iturin, were directly associated with these effects. These modifications indicate both direct and indirect actions of metabolites and compounds on fungal structure, demonstrating an impact beyond simple mycelial inhibition.T. harzianum was the most effective antagonist, especially in direct confrontation, indicating strong mycoparasitic and competitive activity. B. pumilus and A. brasiliense also inhibited pathogen development, mainly through antibiosis associated with soluble metabolites and volatile compounds. Overall, the results indicate that these microorganisms affect Fusarium beyond simple growth suppression, causing structural alterations that reinforce their potential for sustainable biological control of Fusarium wilt.