The Antagonistic Activity of Beneficial Fungi and Mechanisms Underlying Their Protective Effects on Plants Against Phytopathogens

Among the different strategies of plant protection from phytopathogens, the use of beneficial fungi has been described as a sustainable, eco-friendly approach. The aim of the present work was to evaluate the antagonistic activity of beneficial fungal strains in vitro and in vivo. The studied strains (Beauveria bassiana T7, Beauveria bassiana T15, Metarhizium robertsii An1, Talaromyces pinophilus T14) had pronounced antagonistic activity against three phytopathogens (the growth inhibition was 18.2–51%). In pot experiments, the studied strains significantly reduced the level of stress in barley plants caused by phytopathogenic load. The beneficial effect of the strains consisted of an increase in the morphometric parameters of plants and a positive effect on photosynthetic pigments and proline levels. The 1-aminocyclopropane-1-carboxylate deaminase level of the strains varied from 0.95 to 2.73 µM α-KB mg protein−1 h−1. The most significant mechanisms of antagonistic action of the M. robertsii An1 strain were the following: the production of hydrolytic enzymes (chitinase and glucanase activity amounted to 0.23 U mL−1 and 3.42 U mL−1, respectively) and the synthesis of soluble volatile and non-volatile compounds with antifungal properties, including destruxin E, destruxin A, and hydroxyanthraquinones. The results obtained revealed the potential of the studied strains for their integration into a sustainable agricultural system.