Allelopathic effects of fresh and dried leaf extracts of Ageratina adenophora on rice varieties

Plant invasion poses a substantial risk to global biodiversity conservation and economic sustainability. Allelopathy is recognized as a key mechanism through which these invasive plants negatively impact the native flora and fauna. Hence, the present study was designed to investigate the effects of fresh and dry leaf aqueous extracts of Ageratina adenophora in bioassay against two rice varieties. Two rice varieties (namely, Arize 6444 and VNR 2245, hereafter, referred as RV I and RV II, respectively) were selected to study the impacts of A. adenophora on germination and early growth parameters. Mature and healthy fresh leaves of A. adenophora were collected and solutions of 50% and 100% concentrations were prepared, whereas, to prepare dry leaf solutions, leaves were air dried at room temperature and then similar solution concentrations were prepared as for fresh leaves. Ten sterilized and viable seeds per petri plate were randomly placed and prepared leaf solutions i.e. 50% and 100% were added to Petri plates and distilled water was used for the control treatment. Data was recorded for germination and early growth parameters. The Three-Way ANOVA results revealed significant variations in the seedling traits of rice, attributed to the rice variety, extract type, extract concentrations, and their interactive effects. Bioassay results indicated that aqueous extracts of fresh and dry A. adenophora leaves inhibited seed germination, early seedling growth (plumule and radicle emergence), and dry matter accumulation in the tested rice varieties. Significant reductions (p < 0.05) in seed germination, plumule growth, and radicle growth were observed with increasing extract concentrations. At 100% concentration, seed germination decreased by 65–85% for fresh leaf extracts and 74–88% for dry leaf extracts, with variety 6444 (RV I) being more sensitive than variety 2245 (RV II). Moreover, the concentration-dependent inhibition of seedling traits, particularly root length (up to 92% reduction) and plumule growth (up to 69% reduction), was more pronounced in dry leaf extracts. The dry leaf extract exhibited greater inhibition (100%) in all investigated parameters compared to the fresh leaf extract. These findings suggest that the inhibitory effects of A. adenophora leaf extracts are likely due to the allelopathic compounds present in the leaves, which may act independently or synergistically to inhibit plant growth. Rice variety 6444 displayed greater tolerance to the allelopathic effects of A. adenophora leaf extracts, demonstrating more resilience to allelopathic stress. Future research should focus on exploring the potential of A. adenophora leaf extracts in sustainable weed management strategies, while also evaluating their broader ecological impacts in field conditions.