Background: The stem of Syringa pinnatifolia is used as traditional Mongolian medicine for the treatment of cardiopulmonary diseases, in which sesquiterpenes are regarded as the primary medicinal compounds. However, only S. pinnatifolia from natural stands is able to produce medicinal-grade stems when compared with that from cultivated stands. Despite the need to develop an effective technique to promote sesquiterpene accumulation in cultivated stands to ensure sustainable resource production, studies on the potential use of fungal endophytes as fungal elicitors were limited. Objective: This study explored the potential of selected endophytic fungi isolated from the stems of wild and cultivated S. pinnatifolia and further examined their efficacy in promoting sesquiterpene production in S. pinnatifolia calli. Results: Among the 11 fungal groups, Valsa sp, isolated from wild S. pinnatifolia, emerged as a promising fungal elicitor for promoting sesquiterpene accumulation in S. pinnatifolia. This conclusion is drawn from the production of a humulane-type sesquiterpene, known to be one of the most prevalent subtypes of sesquiterpenes in S. pinnatifolia. In addition, it was demonstrated that methyl jasmonate and salicylic acid displayed little effect on sesquiterpene accumulation in S. pinnatifolia. Conclusions: The findings of this study lay a foundation for using fungal endophytes to promote sesquiterpene production in S. pinnatifolia. This contribution could subsequently advance the development of the local traditional medicine industry and aid in the protection of wild S. pinnatifolia.

Syringa oblata is a traditional Mongolian medicine mainly distributed in the Helan Mountains (the boundaries of Inner Mongolia and Ningxia, China) and the north of Yan Mountains (Aohan Qi, Inner Mongolia, China). It is clinically used to treat diseases caused by Heyi, such as heartache and heat pathogen in the heart. Phytochemical studies on S. oblata revealed the presence of iridoids, lignans, triterpenes, phenylpropanoids, phenylethanoids, and volatile components. Pharmacological investigations revealed a broad spectrum of bioactivities, such as antimicrobial, antioxidant, antiproliferative, and hepatoprotective effects. This article summarized the chemical components and pharmacological activities of S. oblata, providing a scientific rationale for its bioactive constituents, quality control, and utilization as an important medicine.