Antifungal Activity of Beauveria bassiana Endophyte against Boxwood Blight Pathogen (Calonectria pseudonaviculata)

Caspian boxwood is one of the most valuable broadleaf evergreen trees in Hyrcanian forests and unfortunately, in the last decade, it has been affected by blight disease caused by the fungus Cylindrocladium buxicola, which is a serious threat to the survival and production of boxwood. Due to the presence of boxwood trees in the forest ecosystems and green spaces of urban areas, safe and environmentally friendly compounds should be used to control the disease. Beauveria bassiana is a plant endophytic fungus with pathogenic ability in insects, whose properties have been proven to increase plant growth, biocontrol pests and limit the activity of phytopathogenic fungi in several host plants. The aim of this study was to investigate the potential of some B. bassiana isolates obtained from the Cydalima perspectalis in controlling the fungus C. buxicola. Antagonistic activity of four isolates of B. bassiana was evaluated using double culture in laboratory conditions and also in the plants by inoculation of endophyte fungus in seeds of plants and inoculation of pathogen fungus in leaves. All four isolates were able to establish endophytic relationship on boxwood seedlings. All isolates showed significant antifungal activity against C. buxicola (53–88%) in vitro. As a result of inoculating the plant with endophytic fungi, a high protective effect against blight fungus was observed and the percentage of leaf damage in boxwood plants inoculated with endophytic fungi was significantly lower than the plants that were inoculated only by the pathogen. The results of this research pave the way for a more effective use of B. bassiana in the integrated and simultaneous management of the leaf–eating pest of Caspian boxwood and the blight fungus of these plants, as well as increasing the growth of the host plant..