Investigation of Effects of Ecological Factors on the Establishment of Azotobacter in the Rhizosphere of Thyme (Thymus vulgaris)

Abstract

Aim: The present study investigates the effect of phosphate-solubilizing bacteria (phosphobacteria (PB) and activity of soil bacteriostasis on the development of Azotobacter in Thymus vulgaris rhizosphere. Place and Duration of Study: The study was conducted at Kenule Beeson Polytechnic botanical garden and at the Science Laboratory Department of the institution for a period of 7months (from March 2018- September 2018).  Methods: The impact of phytohormones produced by phosphate-solubilizing bacteria in vitro and in the rhizosphere of T. vulgaris was used to assay for Azotobacter colonization. Bacteriostasis activity of the soil was determined by comparing the number of Azotobacter microcolonies on discs incubated over soil with respect to those on the controls. Results: Decisive stimulation of Azotobacter population and establishment was observed in Thymus vulgaris rhizosphere when inoculated with phosphobacteria than when inoculated alone as reflected in 5% (0.05) least significant difference. Azotobacter was susceptible to the bacteriostatic factors in potted soils inoculated with it and without (Azotobacter). The increase in susceptibility of this rhizospheric bacteria was time dependent and reached a maximum and thereafter remained almost constant. However, this was overcome by the addition of NPK fertilizer to the plant at some critical stage of the assay. Conclusion: The Presence of nitrogen fixing bacteria (NFB) in vegetation could play significant role in the sustainability and improvement of plant growth and yield. Soil bacteriostasis can also be an important factor that limits the survival and development of NFB.