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Title: Efficacy of bio-activated Zn for improving yield and quality of maize
Keywords: Applied Sciences
Agriculture & related technologies
Issue Date: 2015
Abstract: Zinc (Zn) is an important micronutrient and its adequate supply is considered indispensable for growth, development and normal functioning of plants. In plants, it plays a significant role in photosynthesis, DNA replication, cell division, membrane permeability and integrity, protein synthesis and enzymatic activity, specifically in carbonic anhydrase. Zinc is equally important for human diet and its deficiency affects the immune system, disrupts normal cell growth and reproductive system, and causes skin disorders. Being a co-factor for more than 100 enzymes in human beings, it also provides protection against cancer. Strategies must be employed to increase Zn contents of cereal grains to overcome the Zn deficiency in human beings. Recent reports depict that more than 70% of Pakistani soils are categorized as zinc deficient due to Zn deficient parent material, high soil pH, high calcareousness, more salts and waterlogged conditions and the deficiency passes on to crops as well. Decent amount of zinc is believed to be indispensable for growth and development of maize which is one of the important cereal crops of Pakistan. It is crucial to increase bioavailability of Zn in maize. Among the principal sources used for this purpose, ZnSO4, containing 33% of Zn, is commonly used, but only 4-8 % of the total applied zinc is available to plants while other gets fixed into soil. Furthermore, being expensive, it has economic implications for farmer’s community. Contrarily, zinc oxide (ZnO) is a cheaper and insoluble source which contains 80% of Zn. Bio-activation of insoluble source (ZnO) could be a cost effective method to improve Zn availability from it. Keeping in view the above said problem, the present study was conducted to formulate and evaluate bio-activated zinc for improving yield and quality of maize. For bio-activation purpose, several zinc solubilizing bacteria were isolated from rhizosphere of maize grown soil and quantified on the basis of zinc solubilizing potential and maximum pH reduction in broth medium by the bacterial isolates, finally selecting ten potential zinc solubilizing bacteria. The selected bacterial isolates, capable of solubilizing ZnO, were further screened for their plant growth promoting activity under axenic conditions. Out of ten bacterial isolates, AZ6 was selected for further experiments on the basis of maximum zinc solublization potential, pH reduction and improved growth of maize seedlings. The selected bacterium was later identified as Bacillus sp. AZ6 (Accession No. KT221633), on 16S rRNA gene sequence analysis. The Bacillus sp. AZ6 was characterized for its plant growth promoting attributes. The results implied that Bacillus sp. AZ6 had 1- aminocyclopropane-1-carboxylate deaminase activity and produced siderophores for the biocontrol purpose. Auxins production was also observed by inoculation of Bacillus sp. AZ6 in the presence and absence of L-tryptophan. Bacillus sp. AZ6 also has the ability to produce organic acids like cinamic, ferulic, caffeic, chlorggenic , syrirgic and gallic acids, which were detected on HPLC. These acids solubilized the insoluble source of zinc (ZnO) by lowering pH of broth media. Bacillus sp. AZ6 was used with the organic material (grinded orange peel) to bio-activate the insoluble ZnO with different formulations. Efficient formulations (BOZ1, BOZ2, BOZ3, & BOZ4) were evaluated for temporal release of zinc. With the application of bio-activated zinc formulations, zinc bioavailability was increased significantly as compared to available form (ZnSO4), on the 60th day of incubation. BOZ4 was the most efficient among all for the whole sampling duration (0, 12th, 24th, 36th, 48th, 60th and 72th day). Different combinations varied in their potential for enhancing Zn bioavailability in soil and they were further evaluated in pot and field trials. The pot experiment was conducted to evaluate and compare the different formulations of bioxviii activated zinc with the ZnSO4 on maize crop. Data were analyzed following completely randomized design. Sole application of insoluble source of zinc (ZnO) did not influence the growth, physiological, yield and quality parameters of maize whereas ZnSO4 improved these parameters significantly. Inoculations with zinc solubilizing bacteria also promoted these parameters in most of the cases as compared to control (without zinc) but results were at par with the control. Application of bio-activated zinc formulations had a significant effect on growth (fresh and dry root and shoot biomass), physiology (photosynthetic rate, transpiration rate, stomatal conductance, chlorophyll contents and carbonic anhydrase activity), yield and quality (crude protein, crude fiber, ash, oil contents, dry matter and grain zinc concentration) of maize as compared to ZnSO4 in pot conditions. Among the bio-activated zinc formulations, application of BOZ4 and BOZ3 significantly promoted most of parameters as compared to available form of zinc (ZnSO4). BOZ4 improved grain yield 11% more as compared to ZnSO4. The results of pot trial were confirmed under field conditions by conducting experiments on maize in two seasons (Field trial I in March, Field trial II in July). The results implied that growth, physiology, yield and quality parameters were significantly improved by BOZ4 and BOZ3 formulations as compared to ZnSO4. Data were analyzed following randomized complete block design for field experiments. BOZ4 improved the grain yield in field trial I and II by 10% and 12% respectively as compared to ZnSO4. The combined use of organic material enriched with zinc source (ZnO) and zinc solubilizing bacteria seems to be an effective approach, yet, cost effective, less time consuming and environmental friendly as compared to other zinc sources. Concluding, bio-activation of ZnO is an effective strategy for economical supply of Zn for improving yield and quality of maize, ultimately the farmer’s community can get the maximum profit from their limited resources in addition to biofortification of crop produce with respect to Zn.
Appears in Collections:PhD Thesis of All Public / Private Sector Universities / DAIs.

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