Investigating the Allelopathic Potential of Selected Invasive Plant Species on Native Savanna Plant Germination and Establishment in Kwara State

Allelopathy by invasive plant species is a proposed mechanism for their competitive superiority over native plants, but its empirical characterisation for invasive species affecting Nigerian savanna ecosystems in Kwara State, North Central Nigeria, remains limited. This study investigated the allelopathic potential of three invasive species (Chromolaena odorata, Tithonia diversifolia, and Lantana camara) on the germination and early establishment of five native savanna species (Andropogon gayanus, Daniellia oliveri seedlings, Terminalia laxiflora seedlings, Parkia biglobosa seeds, and Sorghastrum nutans) using aqueous leaf extract bioassays and soil leachate experiments. Aqueous leaf extracts at concentrations of 0, 10, 20, 40, and 80 g/L were applied to seeds and seedlings in Petri dish and pot bioassays. Germination percentage, germination rate, radical length, shoot length, and seedling biomass were recorded at 7 and 21 days. One-way ANOVA and dose-response modelling were applied. Results showed that all three invasive species produced significant allelopathic inhibition of native species germination at concentrations above 20 g/L. Chromolaena odorata extracts produced the strongest inhibition, reducing Andropogon gayanus germination by 78% at 80 g/L. Daniellia oliveri seed germination was the most sensitive of the native targets (IC50 = 12.4 g/L for Chromolaena extracts). Allelopathic effects on shoot elongation were stronger than on germination in three of five native target species. The study provides empirical evidence that allelopathy contributes to the competitive success of invasive plants over native savanna species in Kwara State, and recommends allelopathic impact assessment as part of invasive plant risk screening.

Keywords: allelopathy, invasive plants, Chromolaena odorata, native savanna, Kwara State