Diverse plant growth-promoting bacteria as microsymbionts in nodules of Leucaena leucocephala.

This study characterized 18 endophytic bacterial isolates in association with the root nodules of Leucaena leucocephala through phenotypic and genotypic analyses. The endophytes were associated with the plants and exhibited diverse plant growth-promoting (PGP) traits. Phosphate solubilization was observed in 39% of isolates at high levels and 33.3% at moderate levels. Siderophore production was prevalent, with 38.9% displaying high and 33.3% moderate production, aiding iron uptake. Indole-3-acetic acid (IAA) production varied (32.15 to 86.28 µg/ml) among the isolates. Notably, 94.4% of isolates showed positive hydrogen cyanide (HCN) production. Genetic diversity was assessed using the ARDRA clustered the isolates into eight morphotypes, whereas the phylogenetic analysis of the 16S rDNA sequences showed the presence of different genera including Rhizobium, Paenibacillus, Bacillus, Agrobacterium, Brucella, and Arthrobacter. On the other hand, these symbiotic endophytes are widely recognized for their mechanisms of plant growth promotion. Therefore, net house studies with rhizobial inoculation on L. leucocephala showed significant improvements in growth parameters such as shoot and root lengths, biomass, and nodulation, particularly with the strain Rhizobium sp. SoL9 (T3). Inoculation also enhanced soil properties, increasing nutrient availability and microbial populations. These endophytic bacterial isolates from L. leucocephala root nodules display genetic diversity and beneficial PGP traits, highlighting the potential for rhizobial biofertilization in enhancing plant development and soil fertility in legumes.