Allelopathy and autotoxicity studies and allelochemicals isolation and identification of alfalfa (Medicago sativa L.)

Greenhouse and laboratory studies were conducted to determine short-term and long-term autotoxicity, and allelopathy using alfalfa, grasses, vetch, and weeds. The allelopathic effects of exudates from alfalfa plant parts and the soil in which alfalfa had been grown on alfalfa germination and seedling growth was studied. Based on radicle length growth, the degree of toxicity of different alfalfa plant parts can be classified in order of decreasing inhibition as follows: leaf, seed, complete plant mixture, root, soil, flower, and stem. Alfalfa soil was the most inhibitory to alfalfa growth and these effects were greater for soil collected at the reproductive than the vegetative stage. Seven alfalfa cultivars extracts were screened for autotoxic tolerance on the same cultivar. Based on the concentration of 50% reduction (GI$\sb{50}$), the cultivars may be classified in order of decreasing inhibition. There are genetic differences among cultivars for resistance of alfalfa autotoxicity. In the studies conducted to determine the allelopathic potential of nine grasses to alfalfa germination and growth, tall fescue extracts caused the lowest germination (64%). Timothy extracts caused the lowest survival percent (59%). Dried tops and root extracts of seven different weed species, fresh top and root extracts, were used to study their allelopathic effects on alfalfa in the laboratory. Top growth extracts of weeds exhibited greater allelopathic effects than root extracts. Regression slopes of various top extracts showed significant variation with respect to germination percentage. Velvetleaf extracts were the most inhibitory, while large crabgrass extracts had the least allelopathic effect on alfalfa. Aqueous extracts of alfalfa and vetch exhibited an allelopathic effect on soybean and corn seed germination, seedling length and weight. Secondary root formation and branching were also inhibited as the extract concentration increased. Alfalfa and vetch residue significantly enhanced plant height, leaf area and dry weight of corn. Alfalfa residue exhibited potential natural herbicide when testing its effects on weed seed germination and growth. Giant foxtail was the most resistant species, and lambsquarter was the most susceptible weed species to alfalfa aqueous extracts. As the residue application rate increased, alfalfa dry residue caused significant inhibition and stimulation in the plant height, leaf area, and total dry weight. Alfalfa residue inhibited dicotyledonous more than monocotyledonous weeds. An experiment was conducted to isolate, purify and identify the allelopathic, autotoxic bioactive compounds. HPLC analysis produced peaks with retention times close to those of chlorogenic and salicyclic acid standards. Determination of phytotoxicity by seed germination and seedling growth bioassays suggests that chlorogenic acid may be, at least in part, involved in autotoxicity and allelopathy.U of I OnlyETDs are only available to UIUC Users without author permissio