To evaluate probable allelopathic effect of water extract originated from different parts of russian knapweed (Acroptilon repens L.) on growth of purslane (Portulaca oleracea L.), a factorial experiment was conducted based on randomized complete block design with three replications at greenhouse condition in 2011. Treatments were water extract concentrations (0, 5, 10, 15 and 20 percent) obtained from different part of russian knapweed (aerial part, flower and root). Results showed the significant effect of extract type on seedling length, and extract concentration on shoot length, root length and seedling length. Interaction effect between extract type and concentration on the ratio of root/shoot length, seedling fresh weight, seedling dry weight and germination percentage was significant, too. Means comparison indicated that the longest root (3.55 cm), shoot (4.65 cm) and seedling (8.20 cm) were obtained from control treatment, reducing with higher concentration of extract. The longest shoot (6.95 cm) belonged to extract originated from russian knapweed flowers. The highest ratio of root/shoot length (0.73), seedling fresh weight (0.61g) and seedling dry weight (0.044 g) belonged to control treatment. In general, increasing of extract concentration caused in reduction of germination and seedling traits. Meanwhile, extracts of aerial part had more sever reducing effect than root and flower extracts.

To evaluate probable allelopathic effect of different parts of Russian knapweed (Acroptilon repens L.) on the growth of redroot amaranth (Amaranthus retroflexus L.) seedling, a factorial experiment was conducted based on randomized complete block design with three replications at the Faculty of Agriculture, Urmia University in 2012 (Iran). In this experiment, treatments were different parts of Russian knapweed (aerial part, flower and root) in different amounts (1, 2, 3 and 4 g/pot). Pots included 300 g of soil. Results showed the significant effect of Russian knapweed plant parts on the seedling emergence percent, root length, ratio of root/shoot length, seedling length, seedling fresh weight, and the significant effect of plant material amounts on the seedling emergence percent, seedling fresh weight and seedling dry weight. Interaction effect between plant material type and amount on the shoot length, root length, ratio of root/shoot length, seedling length was significant, too. The longest shoot (3.51 cm), root (1.75 cm), the highest ratio of root/shoot length (0.49) and seedling length (5.26 cm) belonged to control treatment. The highest seedling emergence percent of Amaranthus retroflexus (34.73%) and seedling fresh weight (0.176 g) were occurred at pots treated by Russian knapweed aerial part. The lowest seedling emergence percent (21.94 %) and seedling fresh weight (0.111 g) were obtained from application of Acroptilon repens powdered root. The maximum seedling dry (0.0126 g) and fresh (0.177 g) weight of Amaranthus retroflexus were obtained from control treatment.