allelopathic effects of johnsongrass on germination and early seedling growth of basil, black cumin, cummin, fennel, isabgol and psyllium

the allelopathic effect of weeds frequently inhibited the germination and seedling growth of crops. johnsongrass (sorghum halepens) is known to contain water-soluble substances that are allelopathic. to identify the allelopathic effect of johnsongrass, the effect of different aqueous extracts (0, 5, 10, 20, 30, 40 and 50 g l-1) obtained from roots and leaves of johnsongrass on the seed germination and early seedling growth of some popular medicinal plants of iran [basil (ocimum basilicum), black cumin (nigella sativa), cumin (cuminum cyminum), fennel (foeniculum vulgare), isabgol (plantago ovate) and psyllium (plantago psyllium)] were studied by bioassay. both the root and leaf extracts of johnsongrass in most cases inhibited the seed germination and early seedling growth of isabgol, psyllium, fennel and basil, while the seed germination and the early seedling growth of black cumin and cummin 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 cumin. 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: psyllium, isabgol, fennel, basil, black cumin and cummin.