Antioxidant, antifungal, and aphicidal activity of the triterpenoids spinasterol and 22,23-dihydrospinasterol from leaves of Citrullus colocynthis L

Abstract

Terpenoids from natural plant sources are valuable for their diverse biological activities that have important roles in the medical and agrochemical industries. In this study, we assessed the antioxidant, antifungal, and aphicidal activities of a mixture of spinasterol and 22,23-dihydrospinasterol from the leaves of Citrullus colocynthis. We used 1,1-diphenyl-2-picrylhydrazyl (DPPH) to assess antioxidant activity, and we measured antifungal activity using mycelium growth inhibition assays with three pathogenic fungi, Magnaporthe grisea, Rhizoctonia solani, and Phytophthora infestans. Aphicidal activity against adults of Myzus persicae was determined using in vitro and in vivo assays. Spinasterol and 22,23-dihydrospinasterol exhibited moderate antioxidant activity, even at lower concentrations: 19.98% at 0.78 µg mL^-1, 31.52% at 3.0 µg mL^-1, 36.61% at 12.5 µg mL^-1, and 49.76% at 50 µg mL^-1. Spinasterol and 22,23-dihydrospinasterol showed reasonable levels of fungicidal activity toward R. solani and M. grisea, with EC₅₀ values of 129.5 and 206.1 µg mL^-1, respectively. The positive controls boscalid and carbendazim were highly effective against all fungi except boscalid for M. grisea (EC₅₀ = 868 µg mL^-1) and carbendazim for P. infestans (EC₅₀ = 8721 µg mL^-1). Significant insecticidal activity was observed in both residual and greenhouse assays, with LC₅₀ values of 42.46, 54.86, and 180.9 µg mL^-1 and 32.71, 42.46, and 173.8 µg mL^-1 at 72, 48, and 24 h, respectively. The antioxidant activity of spinasterol and 22,23-dihydrospinasterol was strongly positively correlated with their antifungal and insecticidal activity. Spinasterol and 22,23-dihydrospinasterol therefore show good antioxidant and aphicidal activity with moderate fungicidal activity, making them suitable candidates for an alternative to synthetic agents.