Beauveria bassiana acts as a beneficial endophyte in tea crops, modulating microbial communities and metabolic pathways to enhance plant growth.

The entomopathogenic fungus Beauveria bassiana is renowned for its insecticidal characteristics; however, its capacity as a plant endophyte within tea plants remains incompletely elucidated. This study investigated the colonization of tea plant tissues by B. bassiana and its effects on tea plant growth. It was found that colonization via foliar as well as root application, particularly colonization that persisted in stems for more than 90 days, enhanced growth traits such as plant height, biomass accumulation, and root system development. The foliar spray method resulted in significant changes in the endophytic microbiome and plant metabolism. The colonization had a more significant effect on endophytic fungi than on endophytic bacteria, leading to an increase in the relative abundance of arbuscular mycorrhizal fungi (AMF) in root tissues and a decrease in the relative abundance of total plant pathogens in tea plant tissues. The colonization of tea plants by B. bassiana led to a dynamic reprogramming of secondary metabolism, with an early enhancement in brassinolide and flavonoids to promote growth and enhance antioxidant capacity. As colonization continued, higher levels of catechins and epicatechins supported long-term defense and functional quality. Moreover, the elevation in chorismate indicated enhanced metabolic flux toward defense-related compounds and growth-regulating pathways, contributing to improved plant growth and stress resistance. These results confirm B. bassiana’s ability to act as a versatile bioregulator, expanding our understanding of fungal-plant symbiosis and offering a sustainable method to improve tea cultivation through combined microbial-metabolic reprogramming.