Pheno-morphological and biochemical characterization of root nodules and associated Root nodulating bacteria from Pongamia pinnata (L.) Pierre in the arid regions of India

Vipula Vyas¹Sangeeta Singh^1*Sunil Choudhury²Dr. Tanmaya Kumar Bhoi¹Prithwiraj Dey³Anuj Saraswat^4*

• ¹Forest Protection Division, ICFRE-Arid Forest Research Institute, Jodhpur, Rajasthan, India
• ²S. B.R. M. Government college, Nagaur, Maharashtra, India
• ³Agricultural & Food Engineering Department, Indian Institute of Technology, Kharagpur, West Bengal, India
• ⁴Department of Biology, United Arab Emirates University, Al Ain, United Arab Emirates

Pongamia pinnata (L.) Pierre is a hardy leguminous tree valued for its biofuel potential and ability to thrive in marginal soils through symbiotic nitrogen fixation with root-nodulating bacteria (RNB). This study evaluated the pheno-morphological, soil physico-chemical, and biochemical attributes of twenty RNB isolates (PP-01 to PP-20) associated with P. pinnata in arid regions of western Rajasthan. Rhizospheric soils exhibited alkaline pH (8.2–9.1), moderate EC (1.18–1.89 dS m⁻¹), and variable nutrient contents, reflecting strong spatial heterogeneity. Nodules showed diverse morphology and active nitrogen fixation, while seedling growth varied significantly across isolates, with PP-18, PP-19, and PP-20 performing best. Biochemical profiling revealed wide variation in phenolics, tannins, FRAP, and total antioxidant capacity, with PP-08, PP-09, PP-14, and PP-20 showing superior antioxidant potential. Multiple regression analysis identified nitrogen, potassium, pH, organic carbon, tannin, and antioxidant content as positive contributors to growth, while phosphorus, phenol, and EC exerted negative effects (R² = 0.85). Stepwise regression confirmed nitrogen, pH, organic carbon, and tannin as major positive predictors (R² = 0.61). Principal Component Analysis (PCA) explained 98.8% of total variance, clearly separating isolates based on biochemical and growth attributes, while hierarchical clustering grouped twenty sites into three clusters corresponding to soil fertility gradients. Collectively, results indicate that soil nutrient status and nodule biochemical composition jointly regulate P. pinnata growth under arid conditions. The identified high-performing RNB isolates offer potential for developing site-specific bioinoculants to enhance P. pinnata productivity, soil fertility, and sustainable agroforestry in arid ecosystems.