Isolation, screening, and optimization of the fermentation conditions for endophytic bacteria CHR2-1 of Capparis...

Banana wilt disease, caused by F. oxysporum f. sp. cubense (Foc), poses a severe threat to global banana production. Plant growth-promoting rhizobacteria (PGPR) offer eco-friendly alternatives to chemical fungicides for disease management.

Surface-disinfected root, stem, and leaf tissues of Capparis hainanensis were used to isolate endophytic bacteria. Strain CHR2-1, exhibiting the strongest in vitro antagonistic activity against Foc, was selected. Antifungal mechanisms were evaluated using spore-germination inhibition assays and mycelial growth suppression assays. Greenhouse trials assessed the efficacy of disease control and growth promotion in banana seedlings. Optimal fermentation conditions were determined using response surface methodology. Phylogenetic analysis based on 16S ribosomal RNA (rRNA) gene sequencing identified the strain.

Channelrhodospin 1-2 (CHR2-1) suppressed 9/9 tested plant pathogens, with 88.4% inhibition against Foc. Spore germination inhibition exceeded 80%, while mycelial growth was reduced by 86.38%. In greenhouse trials, CHR2-1 reduced disease incidence by 65.62% (comparable to chemical fungicides) and increased banana-seedling biomass (height: +23.5%; root weight: +31.2%). Optimal fermentation parameters were 10.42 g/L peptone, 1.04 g/L sucrose, pH 7.5, 33 °C, and 180 rpm for 24 h. Phylogenetic analysis confirmed CHR2-1 as Bacillus subtilis.

This study identifies B. subtilis CHR2-1 as a dual-function biocontrol agent with significant potential for sustainable management of banana wilt.