Vegetative Growth Responses of Alfalfa Pathogens to Saponin and Other Extracts from Alfalfa (Medicago sativa L.)1

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Abstract
Various fractions extracted from ‘DuPuits’ and ‘Lahontan’ alfalfas (Medicago sativa L.) were assayed for biological activity on the vegetative growth of 15 alfalfa pathogens, Rhizobium meliloti Dangeard, and Trichoderma viride Pets. ex Ft. Alfalfa plant materials were defatted with hexane‐heptane, followed by extraction with alcohol. The alcohol extracts were further fractionated into chloroform, chloroform‐methanol, butanol, and water fractions. Saponin mixtures were obtained as precipitates from butanol. DuPuits contained more saponin than did Lahontan. Thin‐layer chromatographic analysis revealed the presence of highly complex saponin mixtures in each alfalfa cultivar. Growth responses of the test organisms varied with the organism, the fraction, the source cultivar, and the concentration of the fraction. All test concentrations were below those of saponins naturally occurring in alfalfa. In general, the effects of the four saponin mixtures were similar, with those from DuPuits exhibiting more activity than those from Lahontan. The test organisms varied greatly in their responses to all fractions, i.e., unaffected, stimulated, or inhibited (fungistatic and fungicidal). The nonsaponin fractions greatly affected the growth of the test organisms, but little effect of source variety was noted. The potential role of saponins in disease resistance was discussed.

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