Exploring the Phosphate Solubilising Rhizobacteria isolated from Wild Musa Rhizosphere and their Efficacy on Growth Promotion of Phaseolus vulgaris

Plant growth-promoting rhizobacteria (PGPR) are recognized for enhancing plant growth, protecting against pathogens, and boosting productivity. The present study focused on isolating PGPR from the rhizosphere of wild Musa, screening for growth-promoting traits, and assessing their effects on the growth of Phaseolus vulgaris L. A total of 20 strains were isolated and evaluated for their capacity to solubilize phosphate, produce indole-3-acetic acid (IAA), synthesize siderophores, and their tolerance to salt and heavy metals. Among 20 isolates, four most effective isolates were selected and based on 16S rRNA sequencing these isolates were identified as: Burkholderia cepacia (RZ27), Agrobacterium larrymoorei (RZ23), Pseudomonas taiwanensis (RZ5), and Pseudomonas orientalis (RZ3). P. orientalis exhibited the highest phosphate solubilization ability (222.17 µg/ml), followed closely by B. cepacia (222.80 µg/ml), A. larrymoorei (71.57 µg/ml), and P. taiwanensis (19.20 µg/ml). Isolate RZ27 demonstrated the greatest salt tolerance at 14%, followed by RZ5 and RZ23 (10% each) and RZ3 (6%). Notably, only isolate RZ23 produced IAA, while all isolates except RZ27 could produce siderophores. The highest siderophore production was recorded with RZ23 (33.34% siderophore production unit, SPU), followed by RZ3 (29.07 SPU) and RZ5 (27.20 SPU). A. larrymoorei and P. orientalis showed the highest chromium tolerance (1840 µg/ml), followed by B. cepacia (1810 µg/ml) and P. taiwanensis (1300 µg/ml). There was a noticeable enhancement in plant growth when P. vulgaris was inoculated with the PGPR strains. Among the four isolates, RZ3 significantly increased both shoot and root lengths and biomass compared to the control; meanwhile, isolate RZ23 improved shoot fresh weight. These findings suggest that these isolates have the potential to be used as bioinoculants to improve plant development.