Allelopathy is one of the most important interactions between plants. Weeds are famous plants from this viewpoint, which can decrease crop production in farms by their allelopathic effects. Research has shown that different plant organs have different allelopathic effects. Redroot pigweed (Amaranthus retroflexus L.) is one of the most common weeds with well-known allelopathic potential. This experiment aimed to study the allelopathic effects of different organs' leachate of redroot pigweed on

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... rmination and growth of cucumber (Cucumis sativus L.) and wheat (Triticum aestivum L.) as two important crop species. The effect of different organs' leachate on seed germination and seedlings growth parameters of tested plants was significantly different. In addition, the effects on cucumber were not the same as wheat. According to the results, wheat plant was more resistant at both seed germination and seedling growth stages in comparison to cucumber. Cucumber only showed normal growth potential when treated with the stem leachate, while wheat showed measurable growth potential in all treatments and leaf leachate showed the highest negative effect on wheat. Accordingly, allelopathic effects of redroot pigweed are dependent not only on leachate concentration and plant species, but also on plant organ from which the leachate was released. Therefore, understanding the allelochemical source (organ) of a donor plant is essential for accurate evaluation of allelopathic interactions between plants.