African Journal of
Microbiology Research

  • Abbreviation: Afr. J. Microbiol. Res.
  • Language: English
  • ISSN: 1996-0808
  • DOI: 10.5897/AJMR
  • Start Year: 2007
  • Published Articles: 5093

Full Length Research Paper

Groundnut (Arachis hypogaea L.) and cowpea (Vigna unguiculata L. Walp) growing in Ethiopia are nodulated by diverse rhizobia

Tulu Degefu
  • Tulu Degefu
  • International Crops Research Institute for the Semi-Arid Tropics (ICRISAT-Ethiopia), Addis-Ababa, Ethiopia.
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Endalkachew Wolde-meskel
  • Endalkachew Wolde-meskel
  • International Livestock Research Institute, P. O. Box 5689, Addis Ababa, Ethiopia.
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Zikie Ataro
  • Zikie Ataro
  • Department of Biology, College of Natural and Computational Sciences, Hawassa University, P. O. Box 05, Hawassa, Ethiopia.
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Asnake Fikre
  • Asnake Fikre
  • International Crops Research Institute for the Semi-Arid Tropics (ICRISAT-Ethiopia), Addis-Ababa, Ethiopia.
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Tilahun Amede
  • Tilahun Amede
  • International Crops Research Institute for the Semi-Arid Tropics (ICRISAT-Ethiopia), Addis-Ababa, Ethiopia.
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Chris Ojiewo
  • Chris Ojiewo
  • International Crops Research Institute for the Semi-Arid Tropics (ICRISAT-Ethiopia), Addis-Ababa, Ethiopia.
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  •  Received: 02 November 2017
  •  Accepted: 14 December 2017
  •  Published: 07 March 2018

Abstract

A total of eighty one (81) rhizobial isolates were recovered from root nodules of cowpea (Vigna unguiculata L. Walp.) and groundnut (Arachis hypogaea L.) grown in soils collected from eight different sites (Hawassa, Wondogenet, Chofa, Badawacho, Bodity, Gofa, Ziway, and Alemtena) in Ethiopia with no known history of inoculation. The test isolates together with seven reference strains belonging to five genera including Rhizobium, Ensifer, Mesorhizobium, Bradyrhizobium and Azorhizobium were characterized using ninety phenotypic traits. Thirty one isolates (38%) were found to be fast growers while fifty isolates (62%) were slow growers. The majority of the isolates showed an intrinsic resistance to antibiotics (µg/ml), Chloramphenicol (5 and 15), Lincomycin (100), Novobiocin (0.5 and 1.5), and Erythromycin (10 and 20) and to heavy metals manganese sulphate (500) and copper chloride (100). Most isolates did not tolerate NaCl concentration >3% (w/v) and high temperature (45°C). Dendrogram was constructed by applying the unweighted pair group method with arithmetic means (UPGMA) using NTSYSpc Version 2.1. They were grouped into seven clusters and eight unclustered positions, when 82% relative similarity was used as a cut point. Fifty eight percent of the test isolates were grouped with Bradyrhizobium japonicum and Bradyrhizobium elkanii superclades, thus indicating that rhizobia nodulating cowpea and groundnut are delineated within a branch that defines Bradyrhizobium genus. To elucidate the precise taxonomic positions of the isolates, further genetic studies are required using modern molecular biological methods.

Key words: Groundnut, cowpea, isolates, phenotypic traits, Bradyrhizobium, Rhizobium.