Genetic Diversity and Plant Growth-Promoting Activities of Root-Nodulating Bacteria in Guar Plants Across Jazan Province

Guar (Cyamopsis tetragonoloba L. Taub.) is a significant summer legume used as food for both humans and livestock. In Saudi Arabia, the root nodule bacteria of guar have not been studied. The present work investigated the phenotypic and genetic diversity of guar microsymbionts. Eighty-eight bacterial strains were isolated from the root nodules of guar grown in different locations of Jazan region of Saudi Arabia. The strains were analyzed based on their phenotypic characteristics and variations in their 16S rRNA gene sequences. A significant proportion of the isolates (90%) were fast-growing rhizobia, with 77% showing tolerance to 3–4% NaCl and 91% capable of thriving at temperatures reaching 40 °C. Several isolates exhibited strong plant growth-promoting traits, particularly in IAA production and phosphate solubilization. Genetic analysis indicated considerable diversity, with isolates classified under the genera Rhizobium, Ensifer, Mesorhizobium, Bradyrhizobium, and Agrobacterium. To the best of our knowledge, this study is the first to report on the phenotypic and genetic diversity of guar microsymbionts in Saudi Arabia.