Comparative Phytotoxicity of Aqueous Extracts of Centaurea maculosa and Melilotus officinalis on Germinability and Growth of Wheat

Weed incursion in cultivated fields is a serious biological problem, which causes considerable yield losses of economically important field crops through allelopathy and competitive interactions. Spotted knapweed (Centaurea maculosa) and yellow melilot (Melilotus officinalis) are among the most prevalent weeds in cultivated fields of Pakistan, particularly in wheat fields. Like many other weeds, they may pose allelopathic and competitive challenges to field crops. The objective of this study was to evaluate allelopathic potentials of the two weeds on germination and seedling growth of wheat under laboratory conditions. Amounts of 15, 20, 25 and 30% concentrated leaf aqueous extracts of C. maculosa and M. officinalis were prepared and tested for their effects on germination percentage, radicle and coleoptile lengths of wheat. Germination, radicle and coleoptile lengths of test crop declined significantly at higher concentration (25-30%) of the extracts of two weeds. However, concentration of M. officinalis up to 20% had either no effect or stimulatory effects on the studied growth characteristics of wheat. Highest germination inhibition and decreased seedling growth were caused by leaf extracts of C. maculosa at 30% extract concentration. Growth inhibition was generally dependent on the extract concentration. The study indicated that both plant exhibited allelopathic activity and growth inhibitory effects on wheat at higher concentration; however, extracts of C. maculosa were more phytoinhibitory than M. officinalis. The weeds could serve as potent allelopathic plants for management of other weeds.