Phytotoxic effects of Convolvulus arvensis weed on crops

To investigate the allelopathic effects of Convolvulus arvensis L. on many test plants and to evaluate the presence of allelochemicals in different organs of this weed, laboratory bioassays, greenhouse experiments and chemical analyses were done. The allelopathic potential depended on the plant part (shoots or roots), nature of plant material (water extracts or weed residues in soil), concentration of allelochemicals, selected test plant spp and the physiological process (seed germination or plant growth) studied. Aqueous extracts of C. arvensis roots at higher concentrations significantly reduced the germination of all test crops except cucumber and wheat. While aqueous extracts of shoots, reduced the germination of all test crops, except maize and wheat. The aqueous extracts greatly inhibited the length of primary radicle than seed germination. The lower concentrations were stimulatory in some cases, but the higher ones were most harmful. Incorporation of C. arvensis residues in soil decreased the germination and seedling growth of some test crops. Root residues reduced the germination of cucumber and fresh weight of oilseed rape, but stimulated the fresh weight of maize. While, shoot residues reduced the germination of tomato and wheat and fresh weight of wheat, maize, oilseed rape, sunflower and tomato, but the fresh weight of sugar beet was stimulated. Chemical analyses showed the presence of flavonoids, polyphenols and phenoloid compounds (chlorogenic acid, rutin) and their concentrations were higher in shoots than in roots of C. arvensis. These substances possibly contributes to the observed phytotoxic effects on crops.