Role of ACC-deaminase and/or nitrogen fixing rhizobacteria in growth promotion of wheat (Triticum aestivum L.) under cadmium pollution

Abstract

Excessive cadmium concentrations in agricultural soils result in minimizing the soil fertility and health which leads to decrease in crop production. Plant growth promoting rhizobacteria (PGPR) are beneficial bacteria, which can protect the plants against many abiotic stresses. Current study aimed to identify important rhizobacterial strains by using enrichment technique and examine their inoculation effects on the growth and physiological parameters of wheat, under cadmium pollution. Cadmium was added to 3 kg soil in each pot (with 6 seeds/pot) using cadmium chloride at the rate of 0, 50, 100, 150, and 200 mg kg−1 with three replications in completely randomized design. Rhizobacterial isolates performed considerably better under all cadmium levels, i.e. 50–200 mg kg−1 soil, compared to control. Nevertheless, rhizobacterial isolates containing both abilities, i.e. deaminase and nitrogen fixing, e.g. SAN1 had the highest effect and caused a significant (P < 0.05) increase in the shoot (25.1-fold) and root length (30.2-fold), seedling fresh (17.1-fold) and dry weights (31.1-fold), chlorophyll a (13.1-fold), chlorophyll b (8.2-fold), carotenoids (5.1-fold), protein (50.1-fold), proline (18.8-fold), glutathione S-transferase (26.2-fold), peroxidase (26.8-fold) and catalase (30.5-fold), while lowest cadmium uptake in the shoot (10.1-fold) and root (8.7-fold), respectively, at the highest cadmium level, i.e. 200 mg kg−1 soil compared to control. Results revealed that PGPR significantly decreased the deleterious effects of cadmium pollution by chelating and influencing its bioavailability and increased the wheat growth. The PGPR with both deaminase and nitrogen fixing activities are more resilient against cadmium pollution than PGPR having either deaminase or nitrogen fixing activity alone. The enrichment technique is an efficient approach to select promising PGPR.