Short-term phyto-toxicity consequences of a nonselective herbicide glyphosate (Roundup™) on the growth of onions (Allium cepa Linn.)

This study examined the phyto-toxic effects of a commonly named non-selective herbicide glyphosate (Roundup™) on onions (Allium cepa Linn.). The study was necessitated due to the indiscriminate use and release of Roundup™ for weed control in the Niger Delta soils of Nigeria. The Organisation for Economic Co-operation and Development (OECD) standard protocol # 208 was adopted. The short-term phyto-toxic consequence on onion (A. cepa L.) was determined after a 4-day exposure to varying concentrations of the test chemical at 0.625, 1.25, 2.5, 5 and 10 mg/L, respectively. The percentage growth rate decreased as percentage growth rate inhibition efficiency increased, which implies that the effect of the herbicide was concentration dependent. The mean percentage growth rate inhibition efficiency relative to the control was 28, 47, 61, 73 and 96%, respectively. The effective concentration (EC50) for % Inhibition efficiency was 1.550 mg/L with a 95% confidence interval of 1.269 to 1.848 mg/L. The biological alterations on the onions in the test solutions varied in order of increasing concentrations. Some observations made include decolouration of the test solutions and stunted growth especially at the highest concentration of 10 mg/L. Other effects include: bulb deformation, tissue and root damage. There was significant difference between the exposed species and the control at P < 0.05. The use of the herbicide Roundup™ with such hazardous effects can harm plants especially onion which is a very viable food product of man. This could lead to likely distortion on the ecosystem balance of onions (A. cepa) and similar plants and subsequent effect on human, the major end user.Key words: Herbicide, glyphosate (roundup), onion (Allium cepa Linn.), phytotoxicity