ALLELOPATHIC ACTIVITY OF ROOT SAPONINS FROM ALFALFA (MEDICAGO-SATIVA L) ON WEEDS AND WHEAT

Bioassays were developed for allelopathic effects on dandelion (Taraxacum vulgare), coffeeweed (Sesbania exaltata L.), pigweed (Amaranthus retroflexus L.), barnyard grass (Echinochloa crus-galli L.) and cheat (Bromus secalinus L.) using pure alfalfa (Medicago sativa L., Cimarron cultivar) root saponins containing primarily medicagenic acid glycosides. Liquid secondary ion-mass spectrometry showed this cultivar contained 6 known saponins and several unknown saponins. The saponins were most effective allelopathically toward barnyard grass and cheat, less so for pigweed and coffeeweed, with little effect on dandelions. The alfalfa root saponins were allelopathic toward wheat (Triticum aestivum L.), which was used as the control along with distilled water. The effect of alfalfa root saponins would have in the alfalfa field on the weeds tested remains unclear.