Allelopathic properties of Peganum harmala L.

This doctoral study was conducted to evaluate the allelopathy potential of different plant parts of Peganum harmala L. (Peganum harmala L.) on germination and growth of Amaranthus retroflexus L., Avena fatua L. and Convolvulus arvensis L., as well as identification of the phytotoxic substances responsible for this activity. Results indicate that the water extract of fresh P. harmala plant material had an inhibitory effect on germination and seedling growth of three weed species. As different concentrations of PEG solutions did not show any significant effect on germination and growth of weed species, differences observed for P. harmala extracts were not attributed to osmotic potential of the extract. According to our results, the phytotoxic potential of P. harmala varied with tissues used to prepare the extracts. Among different plant parts used, leaves provoked a greater growth suppression. Total phenolic acids content was higher in leaf extracts when compared to that of stem or root extracts. Greenhouse studies indicate that P. harmala residues incorporated into the soil had potent herbicidal activity and that the activity differed depending on source and amount of residues as well as sensitivity of target species to phytotoxins. Our results also indicate that suppression by P. harmala residues of target weed species was inversely proportional to the time after plant material application, whereas degree of inhibition linked to concentration of phenolic compounds. Overall, results suggest that P. harmala might be used for biological weed control. However, additional work is required to check P. harmala herbicidal activity under different field conditions