Inhibition of Legume Seedling Growth by Residues and Extracts of Quackgrass (Agropyron repens)

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Abstract
Aqueous extracts of quackgrass [Agropyron repens(L.) Beauv. # AGRRE] shoots and rhizomes inhibited seed germination and root growth of alfalfa (Medicago sativaL. ‘Vernal’), soybean (Glycine max(L.) Merr. ‘Corsoy 79’], navybean (Phaseolus vulgarisL. ‘Seafarer’), and curly cress (Lepidium sativumL.) at concentrations of less than 2.5 mg dried extract/ml. Extracts of quackgrass shoots were generally more inhibitory than extracts of rhizomes. Root and shoot dry weights of snapbeans (Phaseolus vulgarisL. ‘Bush Blue Lake’) grown under sterile conditions were reduced by aqueous extracts of shoots. Root systems were stunted and necrotic and lacked root hairs. The growth ofRhizobiumspecies was not influenced by the presence of 40 or 80 mg/ml concentrations of extracts of shoots or rhizomes. Quackgrass may inhibit indirectly the legume-Rhizobiumsymbiosis by inhibiting root hair formation rather than directly inhibitingRhizobiumgrowth. The presence of soil microorganisms was not necessary for the development of quackgrass toxicity in soil or agar. Soil microorganisms reduced toxicity of quackgrass residues in soil.