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dc.contributor.authorAHMAD, IFTIKHAR-
dc.description.abstractCadmium (Cd) is extremely toxic metal which usually causes reduction in plant growth and inhibits native biota. The toxic effects of Cd on plant growth and bacterial community may decrease with the help of different bacterial and organic amendments (bacteria, compost, biogas slurry). Bacterial and organic amendments (BOA) may stabilize Cd in soil and alleviate Cd stress on plants. A series of experiments in controlled and natural environments were conducted to achieve these objectives. Cadmium toxicity may reduce seed germination and seedling growth of wheat and maize. These cereals were exposed to various levels of Cd (0, 5, 20, 50 and 80 mg L-1) to evaluate its effect on seed germination and seedling growth of four wheat and three maize cultivars. Wheat cultivars Sehar-06 and Inqlab-91 whereas maize cultivars SH-919 and PH-3068 was found tolerant and sensitive, respectively to Cd stress. The sensitive cultivars of wheat and maize were further used in successive experiments. The different levels (0, 5, 10, 15 Mg ha-1) each of compost and biogas slurry used to deterimine their effect on growth of sensitive cultivars exposed to different levels of Cd (0, 5, 20, 50, 80 mg kg-1 soil). Compost applied at the rate of 10 and 15 Mg ha-1 significantly increased seedling growth, fresh and dry weight of wheat and maize, respectively, whereas biogas slurry at the rate of 15 Mg ha-1 increased seedling growth, fresh and dry weight of both cereals under Cd stress. Thirty bacterial strains were isolated based on morphology through enrichment technique. Minimum inhibitory concentration of these strains ranged from 200 to 500 mg Cd L-1 on LB plates and out of 30 only 11 strains showed tolerance to 80 mg Cd L-1 in LB broth which were further evaluated for plant growth promoting activity under various Cd levels. Cadmium stress limits plant growth but CTB strains significantly increased wheat and maize growth in normal and Cd contaminated soils. On the basis of maximum point scoring CTB strains CIK-502 and CIK-517Y in wheat whereas CIK-502 and CIK-512 in maize were found most effective in improving growth and biomass of both cereals in normal and Cd contaminated soils. The evaluation of selected BOA based on previous experiments were further assessed in sole and combination for improving wheat and maize productivity, physiology, antioxidant and Cd uptake in Cd contaminated soils (0, 20, 40 mg Cd kg-1) in natural conditions. Growth, yield and physiology of both cereals were rigorously affected by the exogenous application of Cd, however, performance of wheat and maize improved with the application of different BOA under non-stressed and Cd stressed conditions. Application of compost in combination with CIK-502 had maximum increase in growth, yield and physiology of wheat and maize compared to other amendments. The increased physiology, relative water content and water use efficiency whereas decreased electrolyte leakage with the application of BOA conferred their positive role in mitigating Cd stress on both cereals. On the other hand osmolytes and antioxidants increased significantly with the exogenous application of Cd. However, the combined application of different BOA significantly increased osmolytes accumulation especially compost and CIK-502 in both cereals but the activities of CAT, APX and GR greatly differed to Cd stress. The application of different BOA in general decreased CAT, APX, GR and MDA activities. It was observed that Cd accumulated in soil and plant tissues with its increasing exogenous application in soil however BOA significantly reduced its available fraction in soil, and subsequent uptake in root, shoot, grainand total plant of wheat and maize. Cadmium concentration in total plant, root, shoot and grains of wheat and maize decreased with the addition of compost along with CIK-502 and it was the function of AB-DTPA extractable Cd in soil. The BOA was more effectively decreased AB-DTPA extractable Cd in soil in the absence of plants. CTB strains were positive for inodle acetic acid, polyhydroxy butyric acid, P-solubilization, exopolysacharide, NH3-production, ACC-deamianse, catalase and oxidase activities. The complete 16S rRNA gene based identification showed their similarity with genera Klebsiella, Stenotrophomonas, Bacillus and Serratia.en_US
dc.description.sponsorshipHigher Education Commission, Pakistanen_US
dc.subjectApplied Sciencesen_US
dc.subjectAgriculture & related technologiesen_US
dc.subjectSoil sciencesen_US
Appears in Collections:PhD Thesis of All Public / Private Sector Universities / DAIs.

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