A fungal solution to a fungal problem: Chaetomium globosum and Minimedusa polyspora potential in the biocontrol of plant pathogenic fungi

Plant diseases, resulting in an annual estimated loss of 10–15% of world's major crops, represent a major threat to global crops production and social and political stability of nations [1]. About 70–80% of these diseases are caused by pathogenic fungi, numbers that are expected to increase in future years due to the effect of climate change on plant-pathogens interactions [2,3]. In the effort to transition to a more sustainable and resilient agriculture, the application of biological control agents and their secondary metabolites represent a promising option to support the achievement of food security, without further compromise ecosystems’ health [4,5]. Therefore, it is important deepening the potential of known fungal biocontrol agents against the existing fungal pathogens, shedding further light on their action mechanisms and discovering new efficient fungal strains suitable for biotechnological applications. In vitro screenings, despite presenting several limitations, constitute valuable methods for the identification of potential biocontrol agents [6]. Therefore, this study, through an array of in vitro plate assays, aimed at evaluating Minimedusa polyspora (Hotson) Weresub & P. M. LeClair and Chaetomium globosum Kunze ability to inhibit the growth of Alternaria alternata (Fr.) Keissl., Berkeleyomyces basicola (Berk. & Broome) W.J. Nel, Z.W. de Beer, and Botrytis cinerea Pers.. Furthermore, this study aimed also at gaining insights on possible antimicrobial mechanism/s involved in their biological control action. More specifically, a dual culture assay, a dual culture for volatile antimicrobial compounds (performed in two different conditions), and a culture filtrate antifungal activity assay were designed to try to discriminate the impact of direct and indirect biological control mechanisms. This study’s results show that both M. polyspora and C. globosum were able to inhibit, to a different extent, all the pathogens’ growth in the dual culture assay, suggesting a mechanism of biocontrol involving competition for nutrients and space. M. polyspora, based on the culture filtrate antifungal activity assay, was found to exert its inhibition on all the pathogens thanks also to an antibiosis mechanism through the release of diffusible compounds. Moreover, M. polyspora culture filtrate resulted to be particularly effective especially against B. basicola whose growth was completely inhibited; furthermore, its high inhibition effect against this species was also observed in the dual culture for volatile antimicrobial compounds assay, suggesting that M. polyspora antagonism against B. basicola occurs through multiple or mixed mechanisms. Therefore, based on this preliminary study’s results M. polyspora and C. globosum are promising biocontrol agents of three fungal phytopathogens of economical and agronomical relevance, and consequently species of interest for further studies in this area aimed at validating their potential as antagonists in in vivo conditions. 1) J.B. Ristaino, P.K. Anderson, D.P. Bebber, K.A. Brauman, N.J.Cunniffe, N.V. Fedoroff, C. Finegold, K.A. Garrett, C.A. Gilligan, C.M. Jones, et al. (2021). PNAS 118, 23 e2022239118. 2) A.C. Velásquez, C.D.M. Castroverde, S.Y. He (2018) Current Biology 28, 619–634. 3) S. Sarrocco, G. Vannacci (2018) Crop Protection 110, 160–170. 4) R.A.A. Khan, S. Najeeb, S. Hussain, B. Xie, Y. Li (2020) Microorganisms 8, 817. 5) Y. Peng, S.J. Li, J. Yan, Y. Tang, J.P. Cheng, A.J. Gao, X. Yao, J.J. Ruan, B.L. Xu (2021) Frontiers in Microbiology 12, 670135. 6) K. Raymaekers, L. Ponet, D. Holtappels, B. Berckmans, B.P.A. Cammue (2020) Biological Control 144, 104240.