Bioprospecting of Rhizobia as Plant Growth Promoting Rhizobacteria Potential from Root Nodules of Groundnut (Arachis hypogaea L.)

Abstract

Rhizobia are bacteria that symbiosis with host plant, as shown in the root nodules formation, and provide nitrogen that can be absorbed by plants in greater quantities than rhizobacteria. Available Nitrogen, which absorbed by plants, is the essential requirement for plant growth because its role in increasing yield and quality, hence it is needed in greater quantities than other nutrients. The study aimed to determine the macroscopic and microscopic diversity of rhizobia isolates from the groundnut nodules and their potential as PGPRs, and to identify 16S rRNA isolates with the best potential as PGPRs molecularly. The methods used were isolation from root nodules, screening of PGPR potential, molecular identification based on the 16S rRNA gene, and phylogenetic analysis to determine their kinship. Based on the isolation results, 17 Gram-negative isolates were obtained white to pink or orange color on AG media with various colony characteristics in terms of shape, margin, elevation, and texture. KT 20, which was selected as rhizobia isolate with the best potential as PGPR, has ammonium concentration of 23.12 ppm, synthesizes IAA with a concentration of 10.36 ppm, and phosphates solubilization activity, although its ability to synthesize proteases is low. The results of molecular identification of 16S rRNA showed that KT 20 belongs to the Rhizobium genus with a similarity of 99.48 % and bootstrap value of 96 %. HIGHLIGHTS Isolate KT 20 (identified rhizobia) has excellent ability in fixing nitrogen, which plants needs the most and legumes requires in large number Beside the ability of Isolate KT 20 to fix nitrogen, it also able to synthesize IAA, solubilize phosphate, and synthesize protease The ability of isolate KT 20 as PGPR was equal or better than other rhizobacteria that has been analyzed in other in vitro studies GRAPHICAL ABSTRACT