Exploring Multifunctional PGPR from Rhizosphere, Rhizoplane and Root Nodules of Shankapushpi (Clitoria ternatea L.)

Abstract

Plant Growth-Promoting Rhizobacteria (PGPR) boost nutrient availability, root development, and plant health, rendering them environmentally suitable substitutes for chemical-based fertilizers. This study assessed the production of nitrogen fixation, phosphate and potassium solubilization, ammonia and indole-3-acetic acid (IAA) production, siderophore release, and hydrogen cyanide (HCN) production by bacterial isolates previously isolated from the rhizosphere, rhizoplane, and root nodules of Shankapushpi (Clitoria ternatea L.). With greater concentrations of ammonia (183.88 µg/mL), IAA (77.62 µg/mL), siderophore (96.62%), HCN (0.89 µg/mL), and potassium solubilization, RSB20 displayed the highest phosphate solubilization (280 mg/L) among the isolates. The most effective potassium solubilizer was RPB8 (38.23 mg/L; SI 4.07), which also had moderate IAA and high ammonia (175.72 µg/mL). In addition to forming efficient root nodules in Shankapushpi (Clitoria ternatea L.) under Leonard jar experiment, SNB11 showed multifunctionality with high IAA (50.03 µg/mL), robust siderophore production (67.16%), considerable HCN (0.44 µg/mL), and powerful phosphate (SI 4.6) and potassium (SI 2.9) solubilization. Following molecular characterization using 16S rRNA sequencing and phylogenetic analysis, these effective isolates were identified as Bradyrhizobium japonicum (SNB11), Bacillus subtilis (RPB8), and Stenotrophomonas rhizophila (RSB20), all of which are known PGPR strains with established functions in promoting plant growth and nutrient mobilisation. In general, RSB20, RPB8, and SNB11 are viable bioinoculant options for the sustainable cultivation of Shankapushpi (Clitoria ternatea L.).