Noncompetitive Effects of Common Milkweed, Asclepias syriaca L., on Germination and Growth of Grain Sorghum


Common milkweed, Asclepias syriaca L., is a wideranging perennial plant native to North America which is a major weed problem of N-central and northeastern United States and Canada. Previous studies in Nebraska have shown a significant reduction in grain sorghum yield and the number of sorghum plants per hectare caused by milkweed infestations (Evetts, 1971; Evetts and Burnside, 1973). Since these reductions were attributed to competitive mechanisms, we were interested in learning if the yield losses could be, at least in part, due to phytotoxins produced by A. syriaca. Aqueous extracts from fresh fieldcollected milkweed leaves inhibited growth of grain sorghum seedlings. Duplicate experiments with three dilutions of milkweed extract showed the reduction in sorghum dry weight to be proportional to the concentration of milkweed extract. Paper chromatograms prepared with aqueous leaf extracts of milkweed and developed in appropriate solvents showed several compounds which were characterized as phenolics. To determine biological activity, two of these unidentified phenolic compounds were tested with germination bioassays using sorghum and radish seeds. Each compound reduced the germination of the test seeds, with the effects varying according to concentration.


Academic Affairs

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sorghum, seed germination, corn, seedlings, paper chromatography, acid soils, radishes, plant growth, nutrient solutions

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Journal Title

American Midland Naturalist