Role of Rhizobium and Non-Symbiotic Plant Growth Promoting Rhizobacteria in Nitrogen Fixation and Growth of Arachis hypogea: A Review

Abstract

This review aims to synthesize current knowledge on the role of Rhizobium and plant growth-promoting rhizobacteria (PGPR) in enhancing nitrogen fixation and growth in Arachis hypogaea. The environmental and agronomic factors influencing microbial effectiveness, highlights recent advances in biotechnological tools and strain improvement, and discusses challenges related to inoculant application and adoption. By integrating data from laboratory, greenhouse, and field studies, this work aims to provide a comprehensive perspective on leveraging microbial solutions for sustainable peanut production. Rhizobium and PGPR play a vital role in enhancing nitrogen fixation and improving the growth and productivity of Arachis hypogaea (peanut), a globally important legume crop. As an alternative to synthetic nitrogen fertilizers, these soil microorganisms contribute to sustainable agriculture by promoting plant nutrition, improving soil fertility, and supporting environmental health. Rhizobium, particularly Bradyrhizobium spp., forms symbiotic relationships with peanut roots, resulting in the formation of root nodules that fix atmospheric nitrogen. PGPR, including strains of Azospirillum, Pseudomonas, and Bacillus, support plant growth through various mechanisms such as phosphate solubilization, phytohormone production, siderophore secretion, and induction of systemic resistance. Co-inoculation of Rhizobium with PGPR has demonstrated synergistic effects, leading to improved root development, higher nodulation efficiency, increased nitrogen uptake, and enhanced yields under diverse agro-climatic conditions. Despite promising results, several factors limit the consistency and effectiveness of these microbial inoculants, including soil pH, nutrient status, temperature, microbial competition, and host genotype interactions. Issues related to inoculant viability, formulation, delivery, and farmer adoption remain significant constraints. Recent advances in biotechnology, such as genetic manipulation, marker-assisted selection, and omics-based tools, offer new opportunities for strain improvement and a better understanding of plant-microbe interactions. Developing region-specific microbial consortia, improving formulation technologies, and strengthening regulatory frameworks are critical to expanding the use of bioinoculants in legume farming.