Johnsongrass [Sorghum halepense (L.) Pers.] is a dangerous weed causes great losses in agricultural crops. It is difficult to control due to its reproduction by rhizomes, and its resistance to herbicides. This study aims to evaluate the allelopathic performance of five species of cruciferous plants on germination and some growth indicators of Johnsongrass seeds and rhizomes. Cruciferous species are white cabbage, red cabbage, broccoli, turnip, and garden rocket. The aqueous extracts of all these plants were prepared in 2%, 5%, 10%, and 20% concentrations. Germination inhibition rate, shoot, and radicle length of the seedlings of Johnsongrass were calculated over control environment. The powders of whole cruciferous plants were also analyzed using GC-MS. The results showed that garden rocket had the highest effect on the germination inhibition of both seeds and rhizomes. Garden rocket extracts at 10% and 20% concentrations reduced seeds germination by 100%. On the other hand, rhizomes germination inhibition for 10% and 20% concentrations were found 85.3% and 92.7% respectively. The effects of aqueous extracts of cruciferous plants on shoots and radicals were similar to their effects on the germination of Johnsongrass. The allelopathic effect also increased with increasing concentration of the aqueous extract. The most effective cruciferous plant on the biomarkers of Johnsongrass was garden rocket, while red cabbage was the least. The cruciferous plants, especially garden rocket, have a strong allelopathic effect that can be used as an alternative to herbicides in the control of Johnsongrass.
Key words: allelopathy, cruciferous plants, isothiocyanate, Johnsongrass
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