Exploring bacterial cell-free supernatants, unfiltered ferments and crude bacteria uses of Xenorhabdus and Photorhabdus (Morganellaceae) for controlling Botrytis cinerea (Helotiales: Sclerotiniaceae)

Abstract

The pathogen Botrytis cinerea (Helotiales: Sclerotiniaceae) is a wound necrotrophic fungus that causes significant losses in fruits and vegetables worldwide. The entomopathogenic nematode (EPN) symbiotic bacteria, Xenorhabdus spp. and Photorhabdus spp., are well-known associated biological control agents that produce a diverse range of natural antifungal compounds. This study aimed to evaluate the efficacy of different control strategies against B. cinerea using: (i) EPN symbiotic bacterial cell-free supernatants, (ii) unfiltered ferments and (iii) crude bacteria isolates. The antifungal efficacy of X. bovienii, X. nematophila, X. kozodoii and P. laumondii subsp. laumondii cell-free supernatants obtained after the bacterial fermentations were tested in vitro at two different concentrations (10% and 20%). Furthermore, the antifungal effect of X. nematophila and P. laumondii unfiltered ferments were tested in vitro, and their dissuasive effect was also tested over tomato leaves. Finally, the antifungal capacity of the crude X. nematophila and P. laumondii isolate was tested comparing their effect with the fungicide effect of the commercial Bacillus amyloliquefaciens (Serenade® ASO fungicide). The results showed that employing the bacterial cell-free supernatants or the unfiltered ferments could have different antifungal efficacy against this pathogen. Applying X. nematophila cell-free supernatant and unfiltered ferments at 20% concentration resulted in the highest inhibition effect compared with the control (distilled water), 82% and 100%, respectively. Furthermore, P. laumondii-isolate can control the growth of Botrytis in in vitro conditions, showing no significant differences with the efficacy of Bacillus amyloliquefaciens in a four-day experiment. Overall, this study builds on a better understanding of the effects of these novel biocontrol agents against B. cinerea and helps to develop an innovative formulation of these bacterial products as an efficient biocontrol tool.