Inhibition of pitted morning glory (Ipomoea lacunosa L.) and certain other weed species by phytotoxic components of wheat (Triticum aestivum L.) straw.

This study was conducted to determine if well-known phytotoxic effects of plant residues on crop growth could also be responsible for observed reductions of certain weed species in no-till cropping systems. An aqueous extract of field-grown wheat (Triticum aestivum L.) reduced the germination and root length of pitted morning glory (Ipomoea lacunosa L.) and common ragweed (Ambrosia artemisiifolia L.). Phytotoxicity was increased by about 70% when bioassays with the wheat extract on morning glory and ragweed were conducted in the presence of light. Phytotoxic substances were extracted from wheat with 2 N NaOH. The hydrolyzed extract was fractionated by thin-layer chromatography (TLC). The compound isolated by TLC having the greatest inhibitory effects on morning glory germination was identified using mass spectrometry and determined to be ferulic acid (4-hydroxy-3-methoxycinnamic acid). Ferulic acid at 5 × 10(3) M inhibited the germination and root length of morning glory 23 and 82%, respectively, and prickly sida (Sida spinosa L.) with carpels 85 and 82%, respectively. Crabgrass (Digitaria sanguinalis L.) germination was inhibited 100%. Ferulic acid had no effect on ragweed or prickly sida without carpels. Morning glory root and shoot biomass were reduced 52 and 26%, respectively, when morning glory was grown in sand and watered with a 5 × 10(3) M solution of ferulic acid. Ferulic acid in the presence of prickly sida seed carpels was found to undergo decarboxylation, forming a styrene derivative, 2-methoxy-4-ethenylphenol. The more phytotoxic styrene compound was produced by a bacterium isolated from the carpels of prickly sida seed. The study showed that ferulic acid and other compounds may indeed play a role in reducing the growth of certain weeds in no-tillage cropping systems.