Plant growth promoting rhizospheric bacteria associated with Oroxylum indicum (L.) Benth. ex Kurz

Oroxylum indicum (L.) Benth. ex Kurz is a threatened plant species, largely due to overexploitation for its valuable medicinal properties. This study focused on isolating and screening rhizospheric bacteria associated with O. indicum for their plant growth-promoting (PGP) traits, including ammonia production, hydrogen cyanide (HCN) production, indole-3-acetic acid (IAA) production, and phosphate solubilization. Out of 60 bacterial isolates, 35 exhibited one or more PGP activities. Morpho-molecular characterization of these 35 isolates identified seven bacterial species, with relative abundances of 2.86% Enterobacter roggenkampii, 2.86% Pseudomonas taiwanensis, 2.86% Staphylococcus arlettae, 5.71% Bacillus tropicus, 5.71% Bacillus velezensis, 20% Bacillus thuringiensis, and 60% Bacillus cereus. All isolates tested positive for ammonia production, while 51.43% demonstrated phosphate solubilization with varying solubility indices. Additionally, 11.43% of the isolates tested positive for HCN production, and 8.57% for IAA production. The highest IAA production was recorded in Enterobacter roggenkampii (Erog-1) at 5.75 μg/ml, followed by Bacillus tropicus (Btro-7) and Bacillus cereus (Bcer-13) at 0.125 μg/ml. The most effective phosphate solubilizer was Pseudomonas taiwanensis (Ptai-40), with a solubility index of 3.916 ± 0.144 mm, followed by Enterobacter roggenkampii (Erog-1) with an index of 3.076 ± 0.292 mm. Significant variations in PGP activities were observed at the strain level within species. These findings highlight the potential of certain rhizospheric bacteria associated with O. indicum as promising bioinoculants for enhancing plant growth and agricultural productivity.