Alfalfa autotoxic fraction characterization and initial separation

Alfalfa (Medicago sativa L.) has been reported as having autotoxic or autoallelopathic characteristics, but the plant fraction containing the autotoxic material and the responsible compound have not been isolated or identified. Greenhonse and laboratory studies were conducted to: (i) determine if ‘Vangard’ alfalfa exhibits autotoxicity, (ii) determine which plant fraction contains the autotoxic material, and (iii) separate the autotoxic fraction using paper chromatography procedures. In greenhouse studies, alfalfa plant material reduced alfalfa emergence by an average of 87 and 62% in a Kokomo silty loam soil (fine, mixed mesic, Typic Argiaquoll) previously cropped with alfalfa and corn (Zea mays L.), respectively. Incubating the soil and plant material under two contrasting moisture regimes did not alter the inhibitory activity. However, autoclaving the soil and plant material negated the autotoxic response. Laboratory studies indicate that the autotoxic compound was contained within the water-extractable alfalfa fraction, and was not the direct result of microbial activity, although microbial activity may increase the dissipation of the compound. Ascending paper chromatographic separation indicated that the autotoxic compound had an Rf characterization similar to phenolic acid; however, phenolic-absorbent polyvinylpolypryrrolidone did not affect the autotoxic response. The results indicate that alfalfa contains a water-soluble autotoxic compound that has characteristics indicative of a phenolic compound.