Sodicity tolerant polyembryonic mango root stock plants: A putative role of endophytic bacteria

Abstract

The importance of extracellular enzyme producing endophytic bacteria and their ability to elicit ‘induced systemic tolerance’ against abiotic stress (sodic soil) has been documented. However, the performance of these microbes under various abiotic stresses, especially saline-sodic conditions is less understood and formed the focus of this investigation. The diversity of endophytic bacteria associated with leaves, stems and roots of sodicity tolerant polyembryonic mango root stock (GPL-1 and ML-2), grown  at the sodic soil experiment farm (shivery farm), Central Soil Salinity Research Institute, Regional Research Station, Lucknow, India was investigated. In this study, we isolated 16 bacterial endophytes through natural selection from saline sodic soils, analysed extracellular enzyme activity, performed molecular profiling and phylogenetic analysis based on 16S rDNA sequences. Results indicate that the isolates belonged to four major phylogenetic groups: low G+C Gram positive bacteria, Firmicutes, Proteobacteria and Bacteroidetes. Endophytic bacteria from the phylum Firmicutes were predominant in the root portion 60.0% (Na⁺ - 7.72 ± 0.05; K⁺- 2.08 ± 0.85) and stem portion 75.0% (Na⁺ - 5.79 ± 0.05; K⁺- 13.58 ± 0.53), respectively. Most isolates that exhibited extracellular enzymatic activity in 3.0 M NaCl concentration belonged to the genus Bacillus sp., Bacillus clausii, Bacillus pumilus and Bacillus licheniformis (CSR-M-06, CSR-M-08, CSR-M-09 and CSR-M-16) exhibited the stronger activities in extracellular enzymes such as amylase, protease, cellulase and lipase than other isolates.

Key words: Endophytic bacteria, sodicity tolerance, polyembryonic mango, extracellular enzyme activity.