Effect of Glyphosate on Nitrogen Fixing Rhizobium isolated from Root Nodules of Cowpea

摘要

This study was carried out to investigate the effect of glyphosate on Rhizobium spp. isolated from soil in farm land cultivated with cowpeas at Joseph Sarwuan Tarka University, Makurdi. Glyphosate was obtained from Wurukum Markets, Makurdi Metropolis. Standard Microbiological and biochemical laboratory tests were carried out to identify Rhizobium sp. The experimental setup was done by crushing the root nodules and mixing it with the soil sample. The mixture was further divided into 100g in five places in duplicate and labeled as A, B, C, D and E. Samples A, B, C, and D were treated with 10 ml each of 100%, 50 %, 25%, and 12.5% of glyphosate concentration respectively while sample E was used as positive control without treatment. The study results showed that glyphosate impacted the colonies of Rhizobium at different concentrations. Rhizobium sp. colony counts decreased with increased concentration of glyphosate in descending order of 1.53 x 10⁷ CFU/g, 2.12 x10⁶ CFU/g, 2.33 x10⁵ CFU/g, and 2.61 x10³ at 12.5%, 25%, 50% and 10% concentration of Glyphosate respectively. The higher the concentration of glyphosate, the significant reduction in the total colony count of Rhizobium as compared to the control. The colonies were very sensitive to 100% concentration of glyphosate with drastic cell reduction. This study indicates that the effects of Glyphosate on bacterial populations are dose-dependent and highly temporal and this could lead to the rapid enrichment of opportunistic bacteria that use the compound as a nutrient or as a source of Carbon. Glyphosate should be applied in moderate and diluted quantities on farmland.