Amelioration of Heavy Metal Stress in Wheat by Inoculation with Tolerant PGPR and Biochar

Abstract

Wheat is highly sensitive to various biotic and abiotic stresses such as saline stress, drought, heavy metal stress and poor soil fertility. Heavy metals are considered as severe environmental threat particularly for agricultural soils. Heavy metals trigger several cellular to biochemical responses in plants. Present study was designed to isolate and to determine the role of amelioration ability of plant growth promoting rhizobacteria in combination with biochar in wheat crop under heavy metal stress. As plant growth promoting rhizobacteria have the strong ability to tolerate heavy metal stress in medium as well as in contaminated soil. Due to their beneficial PGPR characteristics they can enable the plants to tolerate metal stress and promote growth of crops such as wheat. Biochar is a carbon rich compound formed as a result of thermal deterioration of organic material under oxygen restricted condition. Biochar can act as a strong inoculum medium due to its high porosity and surface area. Furthermore, the biochar can modify the soil structure and nutrient status disturbed due to heavy metal contamination. Soil samples from a heavy metal contaminated site was collected and analyzed by ICPOES and neutron activation analysis. According to findings chromium, nickel and lead exceeded the permissible limit of EPA standards. Furthermore, same soil was used to isolate the PGPR on the basis of their heavy metal tolerance. Total forty-five strains were isolated on the basis of their ability to grow on metal amended media. These strains were further evaluated for the analysis of maximum tolerance limit for heavy metals and PGPR characteristics. Furthermore, twelve strains were selected on the basis of PGPR characteristics and high metal tolerance ability. According to the results of all the functional characteristics for PGPR and heavy metal tolerance ability the three potent PGPR strains were selected to view insight into the molecular mechanism. G6, G11 and G26.1 were preceded further. Two genomes were found to be bacillus and one was pseudomonas spp. Furthermore, the draft genome sequences were submitted in NCBI as bioproject and accession numbers were obtained. Furthermore, these strains were evaluated in combination with 1% biochar, for the amelioration ability of heavy metals such as (1mM NiCl2, 5mM PbNO3 and 0.5 mM K2Cr2O7) in wheat crop. Biochar and PGPR significantly improved the wheat growth and physiological attributes. 98 Furthermore, PGPR and 1% Biochar application significantly reduced the metal uptake in wheat plants. Reduced uptake of Ni upto (0.09±0.07), Chromium upto (0.28±1.01) and Pb upto 0.25±0.01 accumulation in wheat was observed when inoculated with PGPR consortium and 1% Biochar. Hence the combined application of biochar and PGPR proved to be and can act as strong agronomical tools for better plant growth and production. In future as the experimental work produced a reasonable data and these isolated microbes can be applied in industries to prepare a viable inoculum after further analysis and multiplication. Biochar can be used as a fertilizer for low fertile polluted soils which are left abandoned and wasted due to environmental pollutions such as heavy metal. And it can cope up the problems related to artificial fertilizers. Furthermore, as the findings of the thesis, combined application PGPR and biochar in these formulations can also applied in field area to improve the soil fertility, crop yield and reduced hazardous effects of pollutants. Hence the quality and quantity of food crops can be improved. In future this valuable finding should be included and produced further and need more evaluation by new scientists.