Molecular Characteristics of Rhizobia Isolated from Arachis hypogaea Grown under Stress Environment

Rabia Khalid,Rifat Hayat,Mukhtar Ahmed,Xiao Xia Zhang

doi:10.3390/su12156259

Abstract

The phenotypic and genotypic characterization of eight rhizobial isolates obtained from Arachis hypogaea nodules grown under stress environment was performed. Isolates were screened for their ability to tolerate different abiotic stresses (high temperature (60° C), salinity (1–5% (w/v) NaCl), and pH (1–12). The genomic analysis of 16S rRNA and housekeeping genes (atpD, recA, and glnII) demonstrated that native groundnut rhizobia from these stress soils are representatives of fast growers and phylogenetically related to Rhizobium sp. The phenotypic characterization (generation time, carbon source utilization) also revealed the isolates as fast-growing rhizobia. All the isolates can tolerate NaCl up to 3% and were able to grow between 20 and 37 °C with a pH between 5 to 10, indicating that the isolates were alkali and salt-tolerant. The tested isolates effectively utilize mono and disaccharides as carbon source. Out of eight, three rhizobial isolates (BN-20, BN-23, and BN-50) were able to nodulate their host plant, exhibiting their potential to be used as native groundnut rhizobial inoculum. The plant growth promoting characterization of all isolates revealed their effectiveness to solubilize inorganic phosphate (56–290 µg mL−1), synthesize indole acetic acid (IAA) (24–71 µg mL−1), and amplification of nitrogen fixing nifH gene, exploring their ability to be used as groundnut biofertilizer to enhance yield and N2-fixation for the resource poor farmers of rainfed Pothwar region.

Highlights

Salinity is one of the most brutal among abiotic stresses limiting groundnut (Arachis hypogaea L.) productivity
Symbiotic bacteria belonged to genus Allorhizobium [1,2], Azorhizobium [3], Bradyrhizobium [4], Mesorhizobium [5], Rhizobium [6], and Sinorhizobium [7], having the ability to establish a symbiotic relationship with legumes by forming root nodules [8]
Our results have revealed that isolated rhizobial strains have 16S rRNA and housekeeping genes similarity with the members of fast-growing genus Rhizobium

Summary

Introduction

Salinity is one of the most brutal among abiotic stresses limiting groundnut (Arachis hypogaea L.) productivity. The nitrogen fixing bacteria played a vital role in crop production and soil health owing to their ability to fix atmospheric nitrogen, and proved to be environmentally friendly by minimizing pollution problems concerned with the application of chemical fertilizers even under stress conditions. Since more than half of the global N2O emissions originate from agricultural soils because of nitrogen (N) fertilizer use in crop production, it is imperative to minimize these losses by replacing chemical fertilizers with microbial fertilizers. This will help to reduce the carbon footprint [1]. Inoculation of legumes with efficient rhizobia can enhance their ability to fix atmospheric nitrogen, especially when indigenous rhizobial strains are lacking in the soil or they are inefficient [10]

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Discussion

Conclusion