Abstract

This study was carried out to evaluate the effects of different levels of Bonny light crude oil contamination on the germination, shoot growth and rhizobacterial flora ofVigna unguiculata (cowpea) and Arachis hypogea (groundnut) grown in potted sandy loam soil samples in Nsukka, Nigeria. Crude oil at a level of 2.5% increased germination time in cowpea by 24 h but at higher doses (5 to 20%) germination of cowpea seeds was totally inhibited. On the contrary, germination of groundnut seeds occurred at all levels of crude oil pollution although at different rates. The germination time was 7 days in soils with 0.5 to 2.5% oil concentration and an average of 9 days in those with 5 to 20% levels of the pollutant. Even though groundnut germinated and grow in all concentrations of crude oil tested, significant (p<0.05) shoot growth retardation still occurred in both legumes consequent on crude oil toxicity. Rhizobacterial population also diminished with increase in crude oil concentration. The study reveals both the vulnerability of cowpea and the resistance of groundnut to crude oil, marking groundnut out as a promising phytoremediation candidate.

Key words: Crude oil, pollution, rhizobacteria, legume, phytoremediation, rhizosphere.