Synergistic effects of rhizospheric and nodule associated zinc solubilising consortia to enhance productivity and biofortification in lentil (Lens culinaris L.)

Abstract

The present study was undertaken to isolate, screen and evaluate zinc-solubilising bacteria (ZnSB) from lentil rhizosphere and root nodules and to assess their individual and consortium effects on plant growth, yield, micronutrient biofortification and soil nutrient status. A total of 120 rhizospheric soil and 62 root samples were collected from RPCAU research farms at Pusa and Dholi, yielding 157 bacterial isolates. Among these, 127 rhizospheric and 30 nodule isolates were screened for zinc solubilisation using zinc oxide (ZnO) and zinc carbonate (ZnCO₃) as zinc sources. The ZnO was the most preferred substrate, with Zn solubilisation efficiency (Zn-SE) ranging from 25.00 to 416.70 in rhizospheric (Rh) isolates and 57.10 to 357.10 in nodule (Nd) isolates. The most efficient isolates (Rh-ZnSB 38, Rh-ZnSB 60, Rh-ZnSB 90 and Nd-ZnSB 1) also exhibited multiple plant growth-promoting traits, including phosphate and potassium solubilisation, siderophore production, indole-3-acetic acid (IAA) and gibberellic acid (GA) synthesis and ammonia production and were found to be highly compatible with each other. Based on these traits, a microbial consortium was developed. Seed germination studies revealed that combined inoculation of Nd-ZnSB 1 with the Rh-ZnSB consortium resulted in 100 % germination and the highest seed vigour index, indicating strong synergistic effects. Pot experiments further demonstrated that ZnSB consortia significantly enhanced plant growth and nodulation. Plant height ranged from 30.60–38.80 cm at 45 days after sowing (DAS) and 42.10–57.90 cm at 90 DAS, while nodules varied from 18.50–38.90 plant-1 at 45 DAS and 24.30–45.60 plant-1 at 90 DAS, with consortium treatment T₇ consistently outperforming other treatments. Yield attributes were also markedly improved by ZnSB consortia. The number of pods per plant ranged from 50.00 to 75.00, seeds per plant from 69.00 to 130.00, 100-seed weight from 2.40 to 5.30 g and grain yield from 15.00 to 30.00 g pot-1, with maximum values recorded under consortium treatments. Grain biofortification was significantly enhanced, with Zn content ranging from 21.40 to 46.80 mg kg-1 and iron from 62.50 to 102.30 mg kg-1. In addition, ZnSB consortia improved soil fertility by increasing available nitrogen (0.78–1.18 g kg-1), phosphorus (0.32–0.64 g kg-1), potassium (1.15–1.56 g kg-1), organic carbon (0.42–0.66 %) and DTPA-extractable Zn and Fe.