Isolation and Identification of Bacteria Bacillus velezensis with Antagonistic Activity Against Major Pathogens of Coconut

Coconut (<i>Cocos nucifera</i> L.) cultivation is increasingly threatened by destructive fungal pathogens that reduce yield and compromise tree health, particularly in tropical regions in China. To address this challenge, the present study aimed to isolate and identify antagonistic bacteria with potential biocontrol activity against key pathogens of coconut, including <i>Ceratocystis paradoxa</i> (crown rot), <i>Pestalotiopsis menezesiana</i> (leaf blight), and <i>Curvularia oryzae</i> (leaf spot). A total of 65 bacterial strains were isolated from 58 soil samples collected from healthy coconut orchards. Among these, strain X1 exhibited the most vigorous antagonistic activity, with inhibition rates exceeding 70% against multiple pathogens in both plate confrontation and mycelial growth rate assays. Morphological, physiological, biochemical, and molecular (16S rDNA and <i>gyrB</i> gene sequencing) analyses confirmed the identity of strain X1 as <i>Bacillus velezensis</i>. Optimization of fermentation conditions for strain X1 revealed that maximum antimicrobial activity was achieved using a medium containing 2% glucose, 3% peptone, 0.3% NaH₂PO₄·2H₂O, and 0.4% Na₂HPO₄·2H₂O, at 28 °C and pH 7.0-7.5, 5% inoculum, 50-70 mL liquid volume in 250 mL flasks, 72 h fermentation, and agitation at 180-220 rpm. These findings highlight <i>B</i>. <i>velezensis</i> X1 as an up-and-coming biocontrol agent with dual functionalities: effective suppression of coconut fungal pathogens and potential plant growth promotion. Its application could significantly reduce the dependence on synthetic fungicides, offering an eco-friendly alternative for integrated disease management in coconut farming.