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.
The American Midland Naturalist has been published for 90 years by the University of Notre Dame. The connotations of Midland and Naturalist have broadened and its geographic coverage now includes North America with occasional articles from other continents. The old image of naturalist has changed and the journal publishes what Charles Elton aptly termed "scientific natural history" including field and experimental biology. Its significance and breadth of coverage are evident in that the American Midland Naturalist is among the most frequently cited journals in publications on ecology, mammalogy, herpetology, ornithology, ichthyology, parasitology, aquatic and invertebrate biology and other biological disciplines.
Simultaneously an international center for Catholic thought, a teaching-focused liberal arts college, and a dynamic hub for research and scholarship, the College of Arts and Letters at the University of Notre Dame provides its students with an education that fuels their passion for learning while preparing them to make a difference in the world. The largest and oldest college in the university, Arts and Letters houses the divisions of the arts, humanities, and social sciences. It encompasses 21 departments, more than 40 undergraduate and graduate degree programs, and a variety of interdisciplinary centers. Approximately 2,500 undergraduates and 750 graduate students pursue degrees through Arts and Letters programs; students from throughout Notre Dame enroll in thought-provoking Arts and Letters courses.
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The American Midland Naturalist
© 1975 The University of Notre Dame