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Isolation and Biochemical Characterization of Diazotrophs from Wetland Rice

Umme Aminun Naher
Senior Scientific Officer
Soil Science Division, BRRI Gazipur

S. M. Mofizul Islam
Scientific Officer
Soil Science Division, BRRI Gazipur

Abstract/ Executive Summary:

Diazotrophs population ranged from 102 to 107 cfug-1 soil and root of Missing Element trial experiment. Rhizosphere population significantly higher than soil and root endophyte. Isolated diazotroph (strain 17) can fix 37 kgha-1 biological nitrogen and produce 6 mgl-1 of IAA.

Keywords: Diazotrophs, PSB, IAA, Nitrogen managemen.

Location: BRRI experimental farm, Gazipur

Start Date: 01-07-2009

End Date: 30-06-2010

Program Area: Crop-Soil-Water Management

Commodity: Bio fertilizer

Objectives:

To characterize the biochemical predisposition of rice associated diazotrophs and nitrogen fixation capability which will help in efficient nitrogen management for rice production.

Methodology:

Diazotrophs were isolated from three treatments (T₁= Complete fertilizers, NPKSZn @ 138-7-80-3-5 kg/ha, T₄ = Without N and T₁₂ = Fertilizer control) of long-term missing element trial experiment during period of Boro2009. The invitro studies were conducted at the BRRI soil microbiology laboratory, Gazipur. To isolate and estimate the diazotroph populations from soil and rice rhizosphere, a series of 10 fold dilution were prepared up to 10-8. One loop of each dilution was stabbed into 10 ml of semisolid test tube. Diazotrophs populations were determined using most probable number (MPN) method in nitrogen free (Nfb) semi-solid medium. For endophytic diazotrophs, rice root (2-5 g) were washed and surface sterilized with 70% ethanol for 5 minute and then with 3% Clorox for 30 second. The root and stem sample were checked for the efficacy of surface sterilization by rolling them on 0.1% trypic soy agar (TSA) plates. The roots and stem were meshed by using a sterilized mortar and pestle. A 10 fold series of dilution was prepared up to 10-7 and the diazotrophic populations were determined using MPN method in Nfb semisolid medium. The nitrogen fixation capability of the diazotrophs was determined from broth culture by micro Kjeldahl method. Concentration of indoleacetic acid was determined according to Gordon and Weber (1951).

Source of Information: Proceedings of BRRI Annual Internal Review for 2009- 2010

Article Link (Online Journal):

Funding Source:

1. Government

Budget:

Total Budget (Tk.) :

Achievement/Findings:

A number of 45 diazotrophic strains were isolated and enumerated from three different treatments. Irrespective of treatments, the population of diazotrophs found higher in the rhizosphere compared to soil and root. Within three treatments, the higher rhizosphere, soil and endophytic populations were found in complete fertilizer and without N treatments. Comparatively low population found in fertilizer control treatment which proved the nutrient requirement (other than nitrogen) of diazotrophs like other living prokaryotes. The higher diazotrophs population also found in without nitrogen fertilizer applied treatments. This may be due to the capability of nitrogen fixation of these bacteria without nitrogen nutrient which did not hamper their metabolic activity and life process as other required nutrients were available. A number of 17 fast growing diazotrophic strains were selected and tested. Result showed diazotrophs fixed 10 to 37 kgha^-1 nitrogen through BNF. Root endophyte (strain 17) fixed the highest concentration of biological nitrogen. Besides consequences of nitrogen fixation, diazotrophs exhibits plant growth enhancement activities with production of phytohormones such as indoleacetic acid. Isolated diazotrophs were able to produce 4-6 mgl^-1 of IAA. Diazotrophs are capable of producing indoleacetic acid (IAA) that has pronounced effects on plant growth and development. IAA improved amylase activity during rice seed germination, enhanced seedling vigor, speed of germination, and increased seedling length and dry weight. The extensive root growth influences crop growth and development by increasing the plant’s ability to absorb mineral nutrients from large volume of soil.

Knowledge Management: Report/Proceedings