# Evaluation of the Antifungal Potential of Different Photorhabdus Species Against Monilinia laxa and Colletotrichum fioriniae

## TL;DR

This study tests how well different Photorhabdus bacteria can fight two harmful fungi that damage fruit crops, offering a natural alternative to chemical fungicides.

## Contribution

The study identifies specific Photorhabdus strains with strong antifungal activity against Monilinia laxa and Colletotrichum fioriniae.

## Key findings

- P. thracensis 3210 showed the highest antifungal activity against both M. laxa and C. fioriniae.
- Fermentation time and preparation method significantly influenced antifungal effectiveness.
- Higher concentrations of Photorhabdus cultures generally increased inhibition of fungal growth.

## Abstract

Monilinia laxa and Colletotrichum fioriniae are major fungal pathogens causing brown rot and anthracnose in stone fruits and shell fruits, leading to significant economic losses. Chemical fungicides are widely applied but can result in resistance development, environmental contamination, and food safety concerns. Biological control using entomopathogenic bacteria (EPB) of the genus Photorhabdus has emerged as an eco-friendly alternative. This study evaluated the in vitro antifungal activity of selected Photorhabdus species (P. kayaii 1723B, P. temperata 3017, P. cinerea 3086, P. laumondii 3196, and P. thracensis 3210) against M. laxa (M3) and C. fioriniae (VV081) using drop-to-drop confrontation and poisoned agar assays. Effects of fermentation time, preparation mode (original vs. centrifuged and filtered), and concentration (5, 10, 20%) were examined. Species-specific inhibition was observed, with Median Inhibition Index values indicated relatively higher antifungal activity for P. thracensis 3210 against M. laxa (0.718) and C. fioriniae (0.552), followed by P. cinerea 3086 (0.643 and 0.552) and P. kayaii 1723B (0.629 and 0.541). Fermentation time and preparation mode influenced antifungal activity in a strain-dependent manner, with longer fermentation periods and original culture preparations generally showing stronger inhibitory trends. Higher concentrations, especially 20%, were often associated with increased inhibition, although the magnitude of these effects varied among strain–pathogen combinations. Overall, these findings demonstrate that the strain- and pathogen-specific nature of antifungal responses in Photorhabdus, supporting their potential as components of targeted biological control strategies rather than uniform broad-spectrum agents.