Bioassay-guided isolation of antifungal amides against Sclerotinia sclerotiorum from the seeds of Clausena lansium

Clausena lansium (Lour.) Skeels is an attractive shrub or small tree, a member of the Rutaceae family. The seeds, leaves and roots of this plant have been used as herbal medicines for a long time. In this study, seven amides were isolated from the seeds of Clausena lansium. The antifungal assay indicated that lansiumamide B (4) and lansiumamide C (2) displayed the highest antifungal activity against Sclerotinia sclerotiorum with EC50 values of 4.95 and 13.24 μg/mL, which were both lower than that of carbendazim (EC50 = 0.64 μg/mL). The structure-activity relationships of these amides were investigated using assays to measure their in vitro antifungal activities against Sclerotinia sclerotiorum. The effect of the most potent compound lansiumamide B on morphology and physiology of S. sclerotiorum were also evaluated. Lansiumamide B caused cell rupture and mycelial abnormalities of S. sclerotiorum, and its curative efficacy (75.17%) against S. sclerotiorum infection was better than that of carbendazim (56.57%). This study demonstrated that amides isolated from C. lansium possessed the potential to be exploited as botanical fungicides for commercial application or can be used as templates for designing new fungicides with novel action modes.