Crop Science Journal of Natural Resources and Life Sciences Education
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Published in Crop Sci 12:851-856 (1972)
© 1972 Crop Science Society of America
677 S. Segoe Rd., Madison, WI 53711 USA
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Vegetative Growth Responses of Alfalfa Pathogens to Saponin and Other Extracts from Alfalfa (Medicago sativa L.)1

K. T. Leath, K. H. Davis, Jr., M. E. Wall and C. H. Hanson2,3

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.

Key Words: Fungal growth • Disease resistance • Forage quality

1 Contribution No. 247 of the U.S. Regional Pasture Research Laboratory, Plant Science Research Division, ARS, USDA, University Park, Pa., in cooperation with the 12 Northeastern States. This study was supported by ARS, USDA. Contract No. 12-14-100-8930 (34), administered by the Plant Science Research Division, Beltsville, Md.

2 Research Plant Pathologist, U.S. Regional Pasture Research Laboratory, University Park, Pa. 16802; Research Chemist, and Director, Research Triangle Institute, Research Triangle Park, N.C. 27709; and Research Agronomist, PSRD, ARS, USDA, Beltsville, Md. 20705, respectively.

3 The authors wish to thank Dr. M. W. Pedersen for providing the alfalfa meals used in this study, and Dr. R. R. Hill, Jr. for his assistance with the statistical analysis.

Received for publication May 26, 1972.




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