Tea seedlings growth promotion by widely distributed and stress-tolerant PGPR from the acidic soils of the Kangra valley

Abstract

This is the first report of widespread and stress-tolerant PGPR from the tea rhizosphere of the Kangra valley. A total of 493 rhizobacteria were isolated from the major tea-growing regions of the Kangra valley. Molecular fingerprinting of 160 distinct morphotypes using ARDRA and ERIC techniques revealed intergenic and intragenic variability, resulting in the identification of 52 rRNA and 56 ERIC types belonging to 21 distantly related genera, identified by 16S rRNA gene sequencing. Bacillus constituted more than half of the genotypes, followed by Pseudomonas, Burkholderia, Lysinibacillus, Citrobacter, Enterobacter, and Paenibacillus. Bacillus altitudinis, B. cereus, B. megaterium, B. subtilis subsp. inaquosorum, B. methylotropicus, Pseudomonas frederiksbergensis, P. mohnii, and P. moreiii were found to be the most common in the tea rhizosphere across various locations. Quantitative assaying of 42 selected strains revealed significant variations in PGP activities ranging from 55-624 µg/ml for tri-calcium phosphate (TCP) solubilization, 4-3145 nM α-ketobutyrate h/mg/protein ACC-deaminase activity, 2-85 µg/ml IAA-like auxins production, and 2-83% siderophore production. Nine out of 42 PGPR also solubilized aluminium phosphate (Al-P) and iron phosphate (Fe-P). These efficient PGPR are suitable for application in tea soils, which are generally low in available phosphorus, a growth-limiting factor for tea cultivation. Five highly efficient PGPR also showed robust growth under different abiotic stresses under controlled conditions. Inoculum application of 5 efficient and abiotic stress tolerant PGPR showed a significant increment of 1.8-9.4%, 12-16.2%,18.1-30.3% and 21.4-39.2% in plant height, leaf number, fresh and dry weight of tea seedlings under the nursery conditions with 50% reduced NPK concentrations after one year of inoculations, respectively. These selected PGPR genotypes with multifarious PGP activities and natural ability to occur widely can be useful in developing plant microbial inoculants for improving tea productivity.

Keywords: Microbial diversity; Multiple PGP attributes; Phosphate solubilization; Tea rhizosphere.