Inoculation of the Morchella importuna mycosphere with Pseudomonas chlororaphis alleviated a soil-borne disease caused by Paecilomyces penicillatus

Utilising the rhizosphere microbiota as a biological control agent is a promising strategy to protect plants against pathogens, although its efficacy in fungal hosts is uncertain. This study investigated the efficacy of Pseudomonas chlororaphis, a bacterial strain, in mitigating Paecilomyces penicillatus, a soil-borne pathogenic fungus responsible for white mould disease (WMD) in cultivated morels, such as Morchella importuna. Soils with chronic WMD, inoculated with or without P. chlororaphis, were utilised for M. importuna cultivation. In P. chlororaphis-inoculated morel soil beds, P. chlororaphis colonised both the mycelial surface and ascocarp matrix of M. importuna, increasing the abundance of Morchella in soil and the α-diversity of the soil fungal community. Additionally, P. chlororaphis inoculation decreased the abundance of detrimental P. penicillatus and mitigated the WMD incidence, which correspondingly increased the morel yield. Metagenomics revealed that increasing the pseudomonads in the M. importuna mycosphere altered the functionalities of the M. importuna soil microbiota, enhancing the abundances of genes encoding chitinase and alkaline protease and reducing the abundances of genes encoding glucanase and laccase. Under P. chlororaphis inoculation, pathways associated with pathogenic invasion were under-represented in the soil microbiota. These results enhance our understanding of bacterial–fungal interactions within soil ecosystems and demonstrate the potential for disease suppression through microbiota manipulation within the fungal mycosphere. These insights may lead to innovative approaches to combat fungal pathogens and enhance the health and productivity of valuable fungal crops such as morels.