INFLUENCE OF PRIMEXTRA (METOLACHOR AND ATRAZINE) AND GLYPHOSATE ON NODULATION OF BEANS BY RHIZOBIUM SPECIES AND THEIR ABILITY TO SOLUBILIZE PHOSPHATE

Abstract

Cowpea (Vigna uniguiculata), Soybean (Glycine max) and Common bean (Phaseolus vulgaris) belonging to Fabaceae family and some of the dominant crops and pasture legumes grown for human and animal consumption. They are also known for their ability to form a symbiotic association with Rhizobium spp. Cowpea, soybean and common bean were grown on soil with and without herbicides (glyphosate and primextra) at different concentrations ranging from 0.00ml (control) to 1.00ml and 0.00ml (control) to 0.70ml respectively for 30 days. Attempt was made to isolate Rhizobium from the roots of the above stated legumes using standard microbiological technique. The ability of different Rhizobia isolates to solubilize phosphate was carried out using standard technique. Inhibitory activities of Rhizobia isolates on growth of Fusarium oxysporum was carried out in vitro. Influence of primextra and glyphosate on nodulation of roots of cowpea, soybean and common bean was observed after harvesting with hand trowel. The isolate were Rhizobium leguminosarum, Bradyrhizobium japonicum and Rhizobium phaseoli isolated from cowpea, soybean and common bean respectively. Soybean and cowpea showed chlorosis, stunted growth, reduced root length, dry weight and nodules when primextra was applied at highest concentration while common bean seedling remain greenish and healthy. Shoot length, dry weight of shoot and number of nodules in common bean and soybean were lower compared with seedlings grown on soil without glyphosate as concentration increased. Cowpea seedlings appeared greenish at high concentration of glyphosate but there was chlorosis, reduction in root length, dry weight and number of nodules at low and moderate concentrations. Rhizobium leguminosarum CSG3 showed significantly higher concentration of phosphate solubilization of 407.11ug-1 at high concentration of glyphosate. Bradyrhizobium japonicum was also found to showed low concentration of tricalcium in pikovskaya broth when compared to isolate from untreated soil in solubilization of phosphate while Rhizobium leguminosarum CSG3 show superiority in acid phosphatase activity of 34.02Mm/min. This experiment showed that Rhizobium leguminosarum CSP2, Bradyrhizobium japonicum SSP3, Rhizobium leguminosarum CSG2, Bradyrhizobium japonicum SSG1, Rhizobium phaseolus PSG2 exhibited antifungal activity against soil borne pathogen Fusarium oxysporum.There was no nodule formation in soybean seedling and death occurred at high concentration of both herbicides and low solubilization of tricalcium by Bradyrhizobium japonicum recorded in this study showed that glyphosate and primextra at higher concentration should not be used to control weeds in soybean farm. Rhizobium species can be used in bio-control of disease cause by Fusarium spp in plant, also as alternative source of fertilizer for the growth of legumes.