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

## TL;DR

Researchers isolated and optimized a beneficial bacteria from Capparis hainanensis that effectively controls banana wilt disease and promotes plant growth.

## Contribution

A novel Bacillus subtilis strain (CHR2-1) with strong antifungal activity and plant growth promotion was isolated and optimized for fermentation.

## Key findings

- CHR2-1 inhibited spore germination by over 80% and mycelial growth by 86.38% against Foc.
- Greenhouse trials showed a 65.62% reduction in banana wilt disease and increased seedling biomass.
- Optimal fermentation conditions were determined using response surface methodology.

## Abstract

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.