title: Eco-geographical diversity of cowpea bradyrhizobia in Senegal is marked by dominance of two genetic types.
abstract: The genetic diversity of native cowpea rhizobia originating from 60 sites across four eco-geographic zones in Senegal was studied. More than 300 cowpea nodules were analyzed by PCR-RFLP of the 16S-23S rDNA InterGenic Spacer region (IGS). Alignments of IGS sequences indicated that all genotypes were grouping within the Bradyrhizobium genus. The geographical distribution showed that apart from five IGS types, the others were specifically found in only one region. The diversity was significantly higher in the Senegal River valley zone, which presents lower mean annual rainfalls and slightly alkaline soils. Interestingly, two IGS types dominated the Senegalese rhizobial collection, one IGS type (VI) was found on more than half of the nodules collected in the northern Senegal River valley while another IGS type (I) was recovered from the great majority of nodules in the three other regions sampled. Two representative strains from each of these two dominant types were isolated and further analyzed. Multi Locus Sequence Analyses using 6 housekeeping genes indicate that they belong to a new Bradyrhizobium species closely related to B. yuanmingense. Phylogenetic analyses of 2 symbiotic genes nodC and nifH show that they are clustered with B. arachidis. Physiological tests on these strains have shown that under laboratory conditions, the growth of the IGS type VI strains was slightly less affected by a higher osmotic strength in the medium and to alkaline pH, which corroborates the soil physico-chemical parameters.
authors.affiliation: Institut de Recherche pour le Développement (IRD), UR 040, Laboratoire Commun de Microbiologie IRD/ISRA/UCAD, Centre de Recherche de Bel Air, BP 1386, CP 18524 Dakar, Senegal. Electronic address: tania.wade@ird.fr.
authors.forename: Tatiana Krasova
authors.initials: TK
authors.lastname: Wade
authors.affiliation: Institut de Recherche pour le Développement (IRD), Laboratoire des Symbioses Tropicales et Méditerranéennes, UMR113 IRD-Cirad-SupAgro-UM2/USC INRA, Campus de Baillarguet, 34398 Montpellier Cedex 5, France.
authors.forename: Antoine
authors.initials: A
authors.lastname: Le Quéré
authors.affiliation: INRA, Laboratoire des Symbioses Tropicales et Méditerranéennes, UMR113 IRD-Cirad-SupAgro-UM2/USC INRA, Campus de Baillarguet, 34398 Montpellier Cedex 5, France.
authors.forename: Gisèle
authors.initials: G
authors.lastname: Laguerre
authors.affiliation: Institut de Recherche pour le Développement (IRD), Laboratoire des Symbioses Tropicales et Méditerranéennes, UMR113 IRD-Cirad-SupAgro-UM2/USC INRA, Campus de Baillarguet, 34398 Montpellier Cedex 5, France.
authors.forename: Angèle
authors.initials: A
authors.lastname: N'zoué
authors.affiliation: Centre de Suivi Ecologique, Rue Léon Gontran Damas, Fann Résidence, Dakar, Senegal.
authors.forename: Jacques-André
authors.initials: JA
authors.lastname: Ndione
authors.affiliation: Institut de Recherche pour le Développement (IRD), UR 040, Laboratoire Commun de Microbiologie IRD/ISRA/UCAD, Centre de Recherche de Bel Air, BP 1386, CP 18524 Dakar, Senegal.
authors.forename: Francis
authors.initials: F
authors.lastname: Dorego
authors.affiliation: Institut de Recherche pour le Développement (IRD), UMR 195, LEMAR, Dakar, Senegal.
authors.forename: Omar
authors.initials: O
authors.lastname: Sadio
authors.affiliation: Département de Biologie Végétale, Université Cheikh Anta Diop (UCAD)/Laboratoire Commun de Microbiologie IRD/ISRA/UCAD, Dakar, Senegal.
authors.forename: Ibrahima
authors.initials: I
authors.lastname: Ndoye
authors.affiliation: Institut de Recherche pour le Développement (IRD), UR 040, Laboratoire Commun de Microbiologie IRD/ISRA/UCAD, Centre de Recherche de Bel Air, BP 1386, CP 18524 Dakar, Senegal; Institut de Recherche pour le Développement (IRD), Laboratoire des Symbioses Tropicales et Méditerranéennes, UMR113 IRD-Cirad-SupAgro-UM2/USC INRA, Campus de Baillarguet, 34398 Montpellier Cedex 5, France.
authors.forename: Marc
authors.initials: M
authors.lastname: Neyra
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics; D058448:Biota; D020369:Bradyrhizobium / Q000145:classification* / Q000235:genetics* / Q000502:physiology; D003470:Culture Media / Q000737:chemistry; D021903:DNA, Ribosomal Spacer / Q000235:genetics; D007887:Fabaceae / Q000382:microbiology*; D020043:Genes, Essential; D006863:Hydrogen-Ion Concentration; D008969:Molecular Sequence Data; D058885:Multilocus Sequence Typing; D009997:Osmotic Pressure; D058974:Phylogeography; D012150:Polymorphism, Restriction Fragment Length; D053204:Root Nodules, Plant / Q000382:microbiology*; D012675:Senegal; D013312:Stress, Physiological
chemical_list: D001426:Bacterial Proteins; D003470:Culture Media; D021903:DNA, Ribosomal Spacer
keywords: 16S–23S rDNA IGS; Housekeeping genes; Native bradyrhizobia diversity; Vigna unguiculata; nifH; nodC