ALLELOPATHIC EFFECTS OF AQUEOUS LEAF AND ROOT EXTRACTS OF Eucalyptus camaldulensis Dehnh. ON COWPEA GERMINATION AND EARLY SEEDLING GROWTH IN BAUCHI, NIGERIA
Abstract
Eucalyptus camaldulensis Dehnh. is widely cultivated across semi-arid regions of Nigeria due to its rapid biomass accumulation and ecological adaptability. However, its residues may release allelochemicals that impede the performance of adjacent crops. This study evaluated the allelopathic influence of aqueous leaf and root extracts of E. camaldulensis on seed germination and early seedling development of cowpea (Vigna unguiculata [L.] Walp.) under laboratory conditions in Bauchi, Nigeria. The experiment was arranged in a completely randomized design (CRD) with seven treatments replicated four times. The treatments evaluated were: distilled water control (0 g L⁻¹); aqueous leaf extracts at 100 g L⁻¹ (10% w/v), 200 g L⁻¹ (20% w/v), and 300 g L⁻¹ (30% w/v); and aqueous root extracts at 100 g L⁻¹ (10% w/v), 200 g L⁻¹ (20% w/v), and 300 g L⁻¹ (30% w/v). Ten cowpea seeds per replicate were treated daily with the respective preparations. Germination percentage, plumule length, radicle length, and leaf number were recorded. The control treatment recorded the highest germination (90.0%), whereas exposure to 300 g L⁻¹ root extract suppressed germination to its lowest level (45.0%). The 300 g L⁻¹ leaf extract caused the maximum suppression of seedling elongation, yielding the shortest plumule (4.03 cm) and radicle (2.25 cm), compared to 7.45 cm and 4.28 cm in the control, respectively. Treatment effects were statistically significant (P ≤ 0.05) for germination percentage, plumule length, and radicle length, but non-significant for leaf number. These findings confirm that aqueous leaf and root extracts of E. camaldulensis exhibit dose-dependent phytotoxicity against cowpea during early establishment. Field-based evaluations incorporating soil matrices and abiotic profiling are recommended to confirm these laboratory observations under natural environmental conditions.