Enhancement of Ex Vitro Acclimatization in Strawberry Plantlets through Endophytic Сolonization by Beauveria bassiana

Endophytic entomopathogenic fungi such as Beauveria bassiana can serve as effective biostimulants and sustainable alternatives to chemical fertilizers. The interaction between endophytic microorganisms and garden strawberry plants is of particular interest due to the crop’s high sensitivity to abiotic and biotic stresses. This study evaluated the effects of endophytic colonization by B. bassiana on the growth, development, and acclimatization of strawberry plantlets under controlled ex vitro conditions. Inoculation was performed either by pre-soaking plantlet roots or by a single root watering with a B. bassiana conidial suspension (1 × 108 conidia/mL). Colonization rates ranged from 11.3 to 77.5%, depending on the treatment method. B. bassiana treatment enhanced several morphometric parameters, including leaf blade area, root number per plant, shoot height, and shoot and root dry weight, with root watering proving to be the most effective application method. Adaptive responses included higher trichome density on the abaxial leaf surface, increased stomatal number, stomatal size, and stomatal index. In addition, the fungal treatments reduced hydrogen peroxide accumulation. Elemental concentrations were determined by synchrotron radiation X-ray fluorescence analysis using the VEPP-3 storage ring. B. bassiana treatment was associated with increased Mn accumulation in both roots and shoots and higher K and Rb concentrations in roots, whereas Ni, As, Br, and Sr concentrations remained relatively stable between treatments; Ca exhibited a distinct organ-specific distribution pattern, and increased K and Mn levels may be associated with improved osmotic regulation, stomatal functioning, and antioxidant metabolism. Treatment with B. bassiana improved the adaptive potential of strawberry plantlets under ex vitro conditions and may represent a promising biotechnological approach for the production of high-quality planting material.