Allelopathic Effects of Chromolaena odorata Leaf Extracts on the Germination of Cowpea and Maize Seeds

Chromolaena odorata is an invasive weed that is widespread across the Nigerian landscape and is suspected of suppressing crop seed germination through allelopathic chemical release, yet its effects on key staple crops under controlled conditions have not been systematically quantified in Nigerian studies. This study investigated the allelopathic effects of aqueous Chromolaena odorata leaf extracts at concentrations of 0 (control), 25, 50, 75, and 100 g/L on the germination of cowpea (Vigna unguiculata) and maize (Zea mays) seeds. Seeds were placed on filter paper moistened with the respective extract concentrations in Petri dishes and incubated at 27 degrees Celsius for 7 days. Germination percentage, germination rate, radical length, plumule length, and seedling vigour index were recorded. Data were analysed using one-way ANOVA and Tukey's post-hoc test. Results showed that germination percentage of both crops declined significantly with increasing extract concentration. At 100 g/L, cowpea germination declined to 32% and maize to 21%, compared to 96% and 94% in controls. Radical elongation was more sensitive than plumule elongation to allelopathic suppression. Cowpea showed marginally greater tolerance than maize at 25 and 50 g/L concentrations. Seedling vigour index was significantly reduced at all extract concentrations in both crops. The study concludes that Chromolaena odorata exhibits strong allelopathic potential against cowpea and maize germination, emphasising the importance of timely weed management in infested cropping fields across Southern Nigeria.

Keywords: allelopathy, Chromolaena odorata, seed germination, cowpea, maize