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Title: Inoculation with zinc solubilizing rhizobacteria for improving rice (Oryza sativa L.) productivity
Authors: Naseer, Iqra
Keywords: Soil Sciences
Issue Date: 2021
Publisher: Islamia University, Bahawalpur.
Abstract: The human population of the world is increasing on alarming rates especially in developing countries. In these countries, the main source of daily calorie intake is cereal grains that have low quantity of essential nutrients leading towards the malnutrition and under nutrition. Zinc is an important micronutrient and essential for all living organisms on earth. World health organization considered that zinc deficiency is the fifth most important factor of disease and deaths in the developing countries. In Pakistan, seventy percent of agricultural soils are deficient in zinc that results in deficiency of zinc in agricultural produce and ultimately in human beings. Rice is the most important cereal and stable food of more than three billion people in the world. Almost fifty percent of rice crops face the problem of zinc deficiency in the world. Therefore, it is the need of era to enhance the zinc concentration in rice grains. Different strategies are being used to solve the problem of zinc deficiency so that more zinc become available to crop plants. The best stratigy to overcome the problem of zinc deficieny is the use of zinc solubilizing rhizobacteria (ZSB): specific group of bacteria that have the potential to solubilize the fixed or insoluble zinc present in the soil and make it available for plants. The present study was planned to isolate, screen and evaluate the potential of zinc solubilizing rhizobacterial strains for improving the growth, yield and quality of rice. Seventy five pure rhizobacterial isolates were isolated and screened for zinc solubilizing ability. The twenty four zinc solubilizer were further screen for exopolysaccharides and indole-3- acetic acid production. The selected isolates were evaluated in jar trial for their ability to promote the growth of rice seedling under controlled conditions. The results of a jar trial showed that inoculation improved the germination percentage, shoot length, fresh and dry biomass, root length, fresh and dry biomass, root to shoot ratio, tissue water content, soil bacterial population and root colonization. Isolates AN24, AN30, AN31 and AN35 showed the best results for all these measured parameters. The selected isolates were checked for compatibility with each other. The fifteen compatible co-inoculation combinations were selected and further screened in a second jar trial. The results of the second jar trial showed that co-inoculation combinations AN24-AN31, AN30-AN31 and AN30-AN35 performed best in above mentioned parameters. These combinations were selected and further evaluated as sole and co-inoculation in pot and field trials. These strains were identified as Bacillus megaterium strain AN24, Bacillus aryabhattai strain AN30, Bacillus megaterium strain AN31 and Bacillus megaterium strain AN35 with accession number MN005926, MN005927, MN005928 and MN005929 respectively. These selected strains were characterized for different plant growth promoting traits and results revealved that all the strains were gram positive and showed the negative result for oxidase activity. All the tested strains produced siderophores, ammonia, catalase, chitinase, and protease, and hydrolysid the starch. Except Bacillus aryabhattai strain AN30, no one was positive for urease, lipase, cellulase and hydrogen cyanide production. All the four strains solubilized the insoluble tri-calcium phosphate in both qualitative and quantitative assay. All the tested strains produced the citric acid, pyruvic acid, oxalic acid and quercetin. Succinic acid and malonic acid were only produced by Bacillus megaterium strain AN24 while fumaric acid were present only in the metabolite of Bacillus megaterium strain AN31 and Bacillus megaterium strain AN35. Expect Bacillus aryabhattai strain AN30, no single strain produced the gallic acid. The rhizobacterial efficiency to solubilize the insoluble zinc decreased with increasing concentration of zinc in agar plates. The rhizobacterial strains showed the maximum growth at 0.10% zinc concentration that was not toxic or stress-free while 0.25% zinc concentration was relatively toxic and less growth was observed at this zinc level. The results of pot and field trials revealed that sole and co-inoculation with zinc solubilizing strains improved the physical, chemical and biological properties of the soil. The physiological parameters like SPAD value, relative water content, SOD, POD, CAT and APX were maximum improved by co-inoculation combination AN24-AN31. Sole and co-inoculation improved the growth and yield attributes like root length, plant height, root and shoot dry biomass, number of tillers plant-1 , flag leaf and panicle length, panicle weight plant-1 , 100 and 1000 grains weight, grain and straw yield of rice. Inoculation with these strains also improved the concentration of macro (N, P and K) and micronutrients (Fe and Zn) in grains, straw and roots of rice. The co-inoculation combination Bacillus megaterium strain AN24 along with Bacillus megaterium strain AN31 showed maximum improvement in all the measured parameters and maximum biofortified the rice grains with iron and zinc. Hence, it may be concluded that these multi traits strains could be very effective bio-inoculants in improving the soil health and growth, yield and quality of rice under normal as well as in stressed environmental conditions.
Gov't Doc #: 22844
Appears in Collections:PhD Thesis of All Public / Private Sector Universities / DAIs.

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