Phytotoxic Interference of Ageratum conyzoides with Wheat (Triticum aestivum)

Abstract A study was conducted to assess the phytotoxicity of Ageratum conyzoides, a weed of cultivated areas, to the growth and establishment of wheat (Triticum aestivum). The lengths of the radicle and coleoptile and the seedling dry weight of wheat were significantly reduced when wheat was grown in field soil previously infested with A. conyzoides, compared to control soil collected from an area devoid of this weed. Even extracts prepared from A. conyzoides soil were inhibitory, indicating the presence of some water‐soluble phytotoxins in the soil. To determine the possible contribution of the weed in releasing these phytotoxins, growth studies involving leaf residues and their extracts and amended soils (prepared by incorporating leaf residues and residue extracts) were also performed on wheat. With all treatments, an inhibitory effect of A. conyzoides was found, compared to respective controls. A significant amount of water‐soluble phytotoxins (the phenolics) was found to be present in the soil infested with A. conyzoides, leaf residues and the amended soils. The amount of phenolics correlated well with growth performance in the respective treatments. This study establishes the phytotoxicity of leaf residues of A. conyzoides to wheat through the release of phenolics into the soil, which may serve as possible tools in establishing its allelopathy.