Characterization of Bacillus sp. DM16 Isolated from Durian Rhizosphere Soil Exhibiting Antifungal Activity against Colletotrichum sp. and Plant Growth-promoting Traits

Abstract

Background: Anthracnose caused by Colletotrichum spp. is a major fungal disease limiting durian production worldwide. This study aimed to isolate and characterize beneficial bacteria from the durian rhizosphere with both antifungal and plant growth-promoting properties. Methods: Antagonistic activity against Colletotrichum sp. was evaluated using dual-culture, cell-free culture filtrate and volatile organic compound (VOC) assays. Morphological changes in fungal hyphae were examined microscopically. The selected bacterial isolate was identified through morphological, physiological, biochemical and partial 16S rRNA gene sequence analyses. Plant growth-promoting traits, including indole-3-acetic acid (IAA) production, siderophore production, nitrogen fixation and zinc solubilization, were also assessed. Result: Among the isolates obtained, strain DM16 showed the strongest antagonistic activity, inhibiting mycelial growth of Colletotrichum sp. by 57.04±1.52% in dual culture. The strain induced hyphal abnormalities, including swelling, thinning, tip enlargement and reduced branching. Cell-free culture filtrates inhibited fungal growth by 21.62% and 28.83% at concentrations of 5% and 10% (v/v), respectively. VOCs produced by DM16 also significantly suppressed fungal growth, particularly when the bacterium was cultured on TSA medium. Based on phenotypic characteristics and 16S rRNA gene sequence analysis, DM16 was identified as Bacillus sp. In addition, the strain produced IAA (5.5 µg/mL), siderophores, fixed atmospheric nitrogen and solubilized zinc. These results indicate that Bacillus sp. DM16 possesses multifunctional traits associated with biological control and plant growth promotion, highlighting its potential as a sustainable microbial inoculant for integrated disease management and durian production.