Chitosan coacervates with the biocontrol fungus Pochonia chlamydosporia stimulate Musa acuminata growth and inhibit banana Fusarium wilt fungus

Chitosan coacervates were developed using NaOH and evaluated as carriers for the biocontrol fungus Pochonia chlamydosporia (Pc), with the aim of suppressing Fusarium oxysporum f. sp. cubense Tropical Race 4 (FocTR4), the causal agent of banana wilt. Coacervates formed with ≥2% NaOH displayed structural stability, and X-ray diffraction revealed increasing crystallinity with higher NaOH concentrations. When formulated with Pc, coacervates lost part of their crystalline structure and showed unique FTIR peaks, allowing non-destructive detection of the fungus. Nuclear magnetic resonance (NMR) analyses showed progressive release of chitosan monomers over time, which decreased in Pc-loaded coacervates, indicating fungal degradation of the biopolymer. Chitosan coacervates significantly inhibited FocTR4 conidial germination and mycelial growth, while Pc germination remained unaffected. However, high NaOH concentrations compromise Pc mycelial development. Pc development and conidiation were confirmed from 2% NaOH coacervates using a GFP-tagged strain. In planta assays showed that coacervates, unlike chitosan solutions, promoted growth of Musa acuminata and enhanced endophytic root colonization by Pc. These results highlight chitosan coacervates as promising biodegradable delivery systems for microbial biocontrol agents and plant growth promotion in sustainable banana cultivation.