EFFECT OF PHOSPHATE-SOLUBILIZING BACTERIA AND VESICULAR-ARBUSCULAR MYCORRHIZAE ON TOMATO GROWTH AND SOIL MICROBIAL ACTIVITY

The interaction of vesicular-arbuscular mycorrhizae (VAM) and phosphat e-solubilizing bacteria (PSB) on plant growth, soil microbial activiti es, and the production of organic acids was studied in non-sterile soi l containing hydroxyapatite and glucose. Glomus etunicatum (VAM), a fu ngus, and Enterobacter agglomerans, a bacterium able to solubilize ins oluble phosphate, were used as inocula. Three treatments and a control were used: inoculation with E. agglomerans (treatment E), inoculation with G. etunicatum (treatment G), inoculation with E. agglomerans+G. etunicatum (treatment E+G) and the control (C). Inoculation with E, G, or E+G had increased plant growth by days 35, 55, and 75 compared wit h the control. Microbial biomass carbon (C) and alkaline phosphatase a ctivity in the rhizosphere generally increased with time. Alkaline pho sphatase activity was higher in treatments G and Et G compared with th e control at 35 and 55 days. The highest acid phosphatase activity was observed in treatment E at 35 days; however, this markedly decreased with time. A significantly higher soluble phosphorus (P) concentration was observed in treatments E and E+G on day 55 com pared with C. Howe ver, there was no significant difference in soluble P concentration in the rhizosphere between treatments with time. The P concentration was greatest in all treatments on day 55. The highest oxalic acid concen tration was observed in the rhizosphere of the non-sterile soil in E+G on day 35. Total N and P uptake in plants from treatments E and G wer e higher compared with the control. However the highest N and P uptake was observed in treatment E+G. This study suggests a synergistic inte raction between E. agglomerans and G. etunicatum.