Interactive Effects of PGPR and PGR on the Drought Tolerance of Crop Plants Grown in Sandy Soil And Elucidation of Plant Metabolites

Abstract

Worldwide demand for agricultural crop continues to escalate in response to increasing population and damage of prime cropland for cultivation, following soil erosion and urbanization. Research interest is diverted to utilize soils of low or marginal productivity for crop production. Moisture stress has negative effects on crop productivity. The plant growth promoting rhizobacteria (PGPR) and plant growth regulators (PGR) are vital for normal growth and development under moisture stress. The present study was carried out to investigate the role of PGPR and PGR (Salicylic acid and Putrescine) on the physiology of chickpea and wheat grown in sandy soil. Metabolic profiling of leaves of chickpea exposed to moisture stress and treated with consortium of PGR and PGPR were also carried out in order to correlate the role of plant metabolites under various treatments. Liquid chromatographyhigh resolution mass spectrometry (LC-HRMS) analyses was carried out to classify metabolites associated with water stress tolerance in chickpea. To identify the important metabolites associated with drought condition three statistical models i.e. significant analysis of metabolites (SAM), partial least square discriminant analysis (PLS-DA) and random forest (RF) were used. The PGPR, isolated from the rhizosphere of chickpea and wheat were characterized on the basis of colony morphology and biochemical characters viz. Gram staining, P-solubilisation, antibacterial and antifungal activities and catalases and oxidases activities. The PGPR were also screened for the production of indole-3-acetic acid (IAA), hydrogen cyanide (HCN), ammonia (NH3) and exopolysaccharides (EPS). The PGPR P1, P2 and P3 were isolated from the rhizosphere of chickpea while, P4, P5 and P6 were isolated from the rhizosphere of wheat grown in sandy soil. The isolated PGPR strains named as P1, P2, P3, P4, P5 and P6 were identified by 16S-rRNA gene sequencing as Bacillus subtilis, Bacillus thuringiensis, Bacillus megaterium, Planomicrobium chinense, Bacillus cereus and Pseudomonas fluorescence, respectively. The seeds of two chickpea varieties (Punjab Noor2009 and 93127) and wheat varieties (Galaxy-13 and Pak-13) differing in sensitivity to drought were soaked for 2-3 h prior to sowing in 24 h old cultures of isolates. The salicylic acid (SA) and putrescine (Put) were sprayed (150 mg/L), on 20 days old seedlings of both chickpea and wheat. For metabolic profiling of chickpea, leaves from well-watered, waterdeficit and PGPR and PGR treated plants were collected at midday, 14 days (time point 1 at 15% soil moisture content) and 25 days (time point 2 at 6% soil moisture content) after the induction of water stress.