Interaction of chromium (Cr) resistant plant growth promoting rhizobacteria with compost to phytostabilize Cr in spinach rhizosphere

Chromium (Cr) is classified as an ecological toxin, and irrigation of soil with raw industrial effluents causes its concentration in soil and plants to reach fatal levels. Due to reduced metal mobility caused by organic amendment and availability of food for microbial activity, use of Cr-tolerant rhizobacteria in conjunction with compost has proven to be useful in supporting growth and survival of plants. We checked the simultaneous effects of rhizobacteria and compost on spinach (Spinacia oleracea) growth, physiology, biochemistry as well as uptake of Cr. Plants were treated with compost (1 % w/w) and subsequently inoculated with two different PGPR strains under Cr contamination. Among tested inoculants , inoculation of 'JS2 ' strain along with compost significantly ameliorated the adverse effects of Cr on spinach, and improved root and shoot lengths (84 and 197 %), as well as their dry (104 and 89 %) and fresh (89 and 167 %) weights , along with chlorophyll content (84 %) as compared to relative control. In addition, combined application led to a significant increase in antioxidant activities, such as SOD (128 %), CAT (40 %), POD (73 %) and APX (57 %) concomitant with decreased MDA contents (68 %). Data regarding Cr movement from soil to roots and aboveground plant parts, as well as the results of translocation and bioconcentration factors, revealed that combined application of PGPR and compost reduced Cr entry to aboveground plant parts and led to its phytostabilization. Hence, compost and Cr-tolerant PGPR can efficiently immobilize Cr in soil, and reduce its harmful effects on spinach growth, physiology and other important attributes.