Chitosan Biosynthesis and Degradation: A Way to Modulate Plant Defenses in Endophytic Biocontrol Agents?

Nematophagous fungi have been employed in biological control to protect crops of interest because of their ability to manage nematodes sustainably. They are an alternative to the use of synthetic chemical nematicides/fumigants which have negative environmental impact and therefore compromise food security. Depending on their mode of attacking nematodes, the nematophagous fungi are divided into: nematode-trapping, endoparasites, egg- and female-parasites and toxin-producing fungi. Pochonia chlamydosporia (teleomorph Metacordyceps chlamydosporia) has been the most studied fungal parasite of nematode eggs. It is present worldwide, and responsible for natural suppression to plant parasitic nematodes of food security crops. Microbial products of P. chlamydosporia are used for bio-management of plant parasitic nematodes in agroecosystems. Chitosan is a highly deacetylated form of chitin produced after deacetylation. This polymer displays an antimicrobial activity. Entomopathogenic and nematophagous fungi (P. chlamydosporia in particular) are resistant to chitosan, which also increases their conidiation. Chitosan enhances nematode egg-parasitism in vitro by P. chlamydosporia, increasing proteolytic activity and appressoria formation.