Evaluation of Rhizobia and Phosphate Solublizing Rhizobacteria for Enhancing Growth and Yield in Phaseolus Vulgaris L. via Co- Inoculation in Greenhouse and Field
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Date
2014-06
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Addis Ababa Universty
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 noninoculated
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.
Keywords: Common bean, Co-inoculation, Phosphate solubilising rhizobacteria, Rhizobium
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Keywords
Common bean, Co-inoculation, Phosphate solubilising rhizobacteria, Rhizobium