Diverse abietane diterpenoids as multifunctional antimicrobial effects from Salvia castanea.

Background: Phytopathogenic fungal diseases significantly impact the quality of vegetables and fruits in agriculture. Salvia castanea, a Tibetan medicinal plant, possessed anti-inflammatory, antitumor, and antimicrobial activities. Therefore, we investigated the antimicrobial ingredients from this plant and clarified their protective and curative in plants in detail.

Results: Bio-guided isolation of Salvia castanea was conducted to obtain 23 abietane diterpenoids, including three new ones (Castanoids A-C). Most compounds exhibited significant antifungal activity against four fungi. Castanoid C (7) showed remarkable inhibition against Sclerotinia sclerotiorum, Valsa mali, and Botrytis cinerea, with median effective concentration (EC) values of 1.30, 0.84, and 2.40 μg/mL, respectively, outperforming the commercial antifungal agent trifloxystrobin. In vivo, compound 7 demonstrated 100% protective and 82.26 ± 1.07% curative efficiency against Sclerotinia sclerotiorum on rape leaves at 200 μg/mL. At 300 μg/ mL, it effectively controlled tomato rot with 92.65 ± 2.55% protective activity. The observation by transmission electron microscopy disclosed that compound 7 inhibited the growth of fungi by destroying the cell membrane permeability and caused the leakage of cellular components. Additionally, compound 11 exerted potent inhibitory effects against Staphylococcus aureus and Pseudomonas syringae pv. actinidae (Psa) with minimum inhibitory concentration (MIC) value of 6.25 μm, surpassing gentamicin. Its mechanism against Staphylococcus aureus and Psa may also involve membrane damage.

Conclusion: The result highlights the significant antifungal and antibacterial potential of abietane diterpenoids from Salvia castanea, particularly Castanoid C. These findings suggest their broad applicability in agriculture, especially for controlling diseases in rape, apple, and tomato crops. This research provides a foundation for developing natural, effective antimicrobial agents, advancing the field of plant disease management. © 2025 Society of Chemical Industry.