Allelopathy uses, as target plants, the cultivated species that are sometimes considered useful for comparative analysis, but do not naturally co-exist with the donor species (Reigosa et al., 2013) . Therefore, the weed common purslane (portulaca ole
racea) (Portulacaceae) was selected as a target in addition to alfalfa (Medicago sativa) (Fabaceae) to compare with it. Two worldwide distribution weeds: sterile oat (Avena sterilis), and Aleppo grass (Sorghum halepense) (Poaceae) were chosen as donor plants, Water extracts of donor plants were prepared, 2%,4%,8% concentrations were used and distilled water was used for control. Seed germination and early seedling growth of target plants were studied in petri dishes. Lengths of seedlings were measured, after that, following indicators were calculated: Relative seed germination (RSG), relative elongation ratio of Shoot (RERs) and root (RERr), Inhibition percentage of germination, shoot and root length (I), and root/shoot ratio. Means and standard deviation were calculated and means were statically analyzed with one – way ANOVA, LSD test was chosen to compare differences between treatment means at a probability levels (0.01, 0.05). The result showed that extracts had greater effects on seedling growth rather than on germination and all measurements were affected, extracts had inhibition effects on root length of the two tested species, shoot length of alfalfa, but a stimulation effect on shoot length of common purslane. All root / shoot ratios were significant in all treatments of common purslane, and alfalfa treated with Aleppo grass only, while the seed germination differences were generally non – significant, Aleppo grass extracts were more effective than that of sterile oat, and the effect generally increased by increasing concentration.
