Biological activity and chemical isolation of root saponins of six cultivars of alfalfa (Medicago sativa L.)

Wheat, cheat and Trichoderma viride bioassays were used to establish the relationship between the content of biologically active saponins in the roots and the degree of winter dormancy and/or time of six cultivars of alfalfa over the period January to August, 1988. Wheat and cheat bioassay results indicated no significant difforences among cultivars, whereas T. viride was inhibited most by extracts of roots collected during months with high rainfall and rapid growth. Cheast seedling roots were inhibited 8–10% more than those of wheat seedling roots indicating that alfalfa root saponins were more effective as allelopathic compounds in preventing growth of cheat than that of wheat alone. An average of 14 different saponins per cultivar were separated by thin-layer chromatograms. Saponins, and the aglycones produced by acid hydrolysis of the May samples, were separated by thin-layer chromatography. The conclusion is that the amount, structure, and type of saponins present in alfalfa roots vary with time.