Phenotypic and Symbiotic effectiveness of Chickpea (Cicer arietinum L.) Root nodulating Rhizobia from Some Selected Parts of Southeastern Ethiopia
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Date
2016-07-05
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Addis Ababa University
Abstract
Chickpea is the world’s third most important food legume next to bean and soybean. Ethiopia is
the largest producer of chickpea in Africa. However, chickpea production is very low due to poor
soil fertility, poor nodulation and lack of inoculation with effective rhizobia. Although breeding
for improved cultivar for better production and disease resistance has been undertaken for quite a
long time in the country, there was limited research on selection of effective and competitive
chickpea rhizobia for inoculant production to fully realize the benefits of biological nitrogen
fixation. In this study, soil and nodule samples were collected from 60 sampling sites from
chickpea growing areas of the eastern, southeastern and southern parts of the country to collect
39 root nodule bacteria. Based upon presumptive and definitive (authentication tests), only 23
isolates (59%) were root nodule bacteria. Out of the authenticated rhizobia, 14 isolates (61%)
were categorized as either highly effective (17%) and effective (44%) with shoot dry matter
accumulation of 80-100% and 50-80% in relation to the nitrogen-fertilized control plants,
respectively. The inoculated plants showed diversity in nodule number, nodule dry weight and
shoot dry weight. Accordingly, the isolates induced 14-62 nodules/plant with nodule dry weight
of 20-53.3 mg/pt; and shoot dry matter of 250-417mg/Pt, respectively. The isolates were fast
growing and acid producing rhizobia with growth rate of 1-2.8 hr, and changed the YEMA-BTB
medium into yellow that can be tentatively grouped into the genus Mesorhizobium. They failed
to solubilize inorganic phosphate on Pikovskaya’s medium. The isolates were also screened in
vitro for their nutritional versatility and eco-physiological tolerance for preliminary taxonomic
screening and as markers for selection of ecologically competent isolates for inoculation study in
the field. Accordingly, the isolates utilized most of the tested carbohydrates and amino acids
except lactose and glycine. The chickpea rhizobia, with few exceptions were tolerant to
moderately acidic and near neutral pH (pH 6.5-8.0), relatively salt tolerant (1-3% NaCl) and
mildly temperature resistant (10-30oC). Most of the isolates were sensitive to the antibiotics
chloramphenicol and Penicillin G, to heavy metals Hg and Cu. However they showed inherent
resistance to Bacitracine, gentamycine, Al and Mn. Based on the combined pattern of nutritional
and ecological tolerance with symbiotic effectiveness, isolates EIARCP7, EIARCP13,
EIARCP8, EIARCP10, EIARCP11, and EIARCP18 combined the best match of high symbiotic
effectiveness with a wide range of resistance to eco-physiological stresses under laboratory
conditions and may qualify to be potential candidates for a field trial in the future.
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Keywords
Endosymbionts, Isolates, Mesorhizobia, Nodulation Efficiency