Inhibitory effects of Sorghum halepens root and leaf extracts on germination and early seedling growth of widely used medicinal plants.

To identify the allelopathic effect of Sorghum halepens, the effect of different aqueous extracts (0, 5, 10, 20, 30, 40 and 50 g L) obtained from roots and leaves of Sorghum halepens on the seed germination and early seedling growth of some popular medicinal plants of Iran (Ocimum basilicum, Nigella sativa, Cuminum cyminum, Foeniculum vulgare, Plantago ovata and Plantago psyllium) were studied by bioassay. Both the root and leaf extracts of Sorghum halepens in most cases inhibited the seed germination and early seedling growth of Plantago ovata, Plantago psyllium, Foeniculum vulgare and Ocimum basilicum, while the seed germination and the early seedling growth of Nigella sativa and Cuminum cyminum was simulated by both extracts at lower concentrations. However, this advantage was not found in higher concentrations, at which the extracts mostly had a negative effect on Nigella sativa and Cuminum cyminum. Leaf extracts was more effective to germination and early seedling growth than the root extract. The effectiveness of these extracts on the root growth was greater than that of the shoot growth of the test plants. The degree of sensitivity can be classified averaged across all extract concentrations in order of decreasing inhibition as follow: Plantago psyllium, Plantago ovata, Foeniculum vulgare, Ocimum basilicum, Nigella sativa and Cuminum cyminum. Growth studies conducted in soil amended with different amounts of Sorghum halepens residues also reveled phytotoxic effects of residues on seed germination and seedling development of Plantago ovata and Nigella sativa.