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Title: Screening Rhizobia and Phosphate Solublizing Rhizobacteria for Enhancing Plant Growth and Grain Yield in Common Bean (Phaseolus Vulgaris L.)
???metadata.dc.contributor.*???: Asst. Prof. Fassil Assefa
Tesfaye, Getaneh
Keywords: Common Bean;Co-Inoculation;Phosphate Solubilising Rhizobacteria;Rhizobium
Issue Date: Mar-2017
Publisher: Addis Ababa University
Abstract: The symbiotic nitrogen fixing effectiveness of common bean nodulating rhizobia and phosphate solubilizing abilities of rhizospheric bacteria collected from the major growing areas of Ethiopia were evaluated. Soil samples were randomly collected from farmers’ fields. Isolation of rhizobia was conducted using plant infection method in greenhouse whereas the phosphate solubilizing rhizobacteria (PSR) were isolated from the soils adhering to the root surfaces of common bean. Authentication, phenotypic characterization and symbiotic efficiency of 76 rhizobial isolates were determined following standard methods. PSR were screened for solubilization efficiency on solid and liquid media containing different phosphate sources. All the PSR and rhizobia were tested for other plant growth promoting (PGP) traits. Single- and co-inoculation trials with rhizobial and phosphobacterial isolates were conducted under greenhouse and field trials. Analysis of 16S rRNA gene sequences was performed to identify the top two symbiotically effective rhizobial isolates and all the PSR. The rhizobial isolates, except CBR039 and CBR151, were able to reinfect their host plant. The rhizobia displayed diversity in their phenotypic characteristics and formed four clusters with reference strains that include R.phaseoli, R.etli, R. gardiani and R. tropici. The two rhizobial isolates, CBR052 and CBR141, with high symbiotic efficiency were identified as Rhizobium etli and Rhizobium sp., respectively. Fifty six PSR were isolated in this study and identified into 10 genera that include Bacillus, Arthrobacter, Brevibacterium, Lycinibacillus, Enterobacter, Acetinobacter, Pseudomonas, Klebsiella, Devosia, and Chryseobacterium. The phosphobacteria released as much as 312.7 μg/ml soluble phosphate from tri-calcium phosphate (TCP). As high as 53.2μg/ml IAA production and 51.3% Fusarium inhibition was recorded in this experiment. Inoculation of common bean with selected phosphobacterial isolates in greenhouse significantly (p<0.05) improved nodulation, nitrogen fixation and other plant growth parameters. Rhizobium-PSR co-inoculations significantly(P<0.05) increased the nodulation, shoot dry weight, shoot nitrogen, and grain yield compared to both single Rhizobium inoculation and the uninoculated control plants in each of the three varieties. The effect of co-inoculation with CBR052 + PGPRC27 on yield and other growth parameters was the highest on all the varieties. The 1436.35 kg/ha yield recorded in the non-inoculated control was increased to 2118.42 kg/ha (47.5%) due to CBR052 single inoculation and this was further raised to 2694.32 kg/ha (87.6%) by the combined inoculation of CBR052 + PGPRC27 on Ibaddo variety at Melkassa site. There was also significant (P< 0.05) variability in yield and other plant development responses among the studied common bean varieties as result of inoculation and co-inoculation. Ibadoo was found to be the best-responding variety for the applied bacterial treatments. These findings could therefore reinforce the understanding on interactions between rhizobia, PGPR and the host plant varieties so that as high as 95% more crop yield in common bean could be achieved through co-inoculation of selected strains
Description: Academic dissertation submitted to the School of Graduate Studies of Addis Ababa University, in partial fulfillment of the requirements for the Degree of Doctor of Philosophy in Biology (Applied Microbiology).
Appears in Collections:Thesis- Microbial, Cellular and Molecular Biology

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