Allelopathic activity of the Oxalis europea L. extracts on the growth of eight test plant species

Oxalis europea (Oxalidaceae) is an annual weed widely distributed in tropical and sub-tropical regions. A common wheat field weed, O. europea was studied to evaluate its allelopathic potential. Aqueous methanol extracts of O. europea were applied to cress, rapeseed, alfalfa, lettuce, Italian ryegrass, barnyard grass, foxtail fescue and timothy at six different concentrations to assess their effect on seedling growth. At a concentration ≥ 0.003 g dry weight equivalent extract/ml, the O. europea extracts significantly inhibited the shoot and root growth of all the test plant species with the exception of the root growth in cress. There was a significant negative correlation coefficient (R) between the concentration of the O. europea extracts and seedling length. The concentration needed to produce a growth inhibition of 50% of the all test plant species was in the range of 0.002 to 0.026 g dry weight equivalent extract/ml for shoot growth and 0.002 to 0.018 g dry weight equivalent extract/ml for root growth. The lettuce shoots and roots were more sensitive to the extracts, whereas the barnyard grass shoots and cress roots were less sensitive to the extracts of O. europea. These findings indicate that O. europea may have allelopathic activity and may contain growth inhibitory substances. Thus, O. europea is a potential candidate for isolating and identifying allelochemicals to develop environment-friendly bio-herbicides to control weeds.