African Journal of
Biotechnology

  • Abbreviation: Afr. J. Biotechnol.
  • Language: English
  • ISSN: 1684-5315
  • DOI: 10.5897/AJB
  • Start Year: 2002
  • Published Articles: 12191

Full Length Research Paper

Diversity of indigeneous bradyrhizobia associated with three cowpea cultivars (Vigna unguiculata (L.) Walp.) grown under limited and favorable water conditions in Senegal (West Africa)

Tatiana Krasova-Wade1, 2, *, Ibrahima Ndoye1, 2, Serge Braconnier3, Benoit Sarr3, Philippe de Lajudie4 and Marc Neyra1
  1Laboratoire de Microbiologie, IRD, BP 1386, Dakar, Senegal 2Département de Biologie Végétale, Université Cheikh Anta Diop, BP 5005, Dakar, Senegal 3Centre d’Etude Régional pour l’Amélioration de l’Adaptation à la Sécheresse (CERAAS), BP 3320, Thiès Escale, Thies 4Laboratoire des Symbioses Tropicales et Méditerranéennes (LSTM), Campus de Baillarguet, TA10/J, 34398 Montpellier Cedex 5, France
Email: [email protected]

  •  Accepted: 17 December 2002
  •  Published: 31 January 2003

Abstract

 

The diversity of Bradyrhizobium strains nodulating three cowpea (Vigna unguiculataL. Walp.) cultivars in favorable and water-limited conditions occuring at flowering was analysed. PCR- Restriction Fragment Length Polymorphism (PCR-RFLP) analysis of 16S-23S rDNA intergenic spacer region (IGS) directly applied on 85 crushed nodules distinguished four genetic profiles, IGS types I, II, III and IV. The distribution of these IGS types according to water conditions and cowpea cultivars (B-21, TN 88-63 and Mouride) showed that nodulating strains appeared more diverse in water-limited condition. More than three quarters of prospected nodules presented the IGS type I. They were formed on all three cultivars and in both water conditions. Only a small part of nodules was distributed between the IGS type II, III and IV. Nodules showing the IGS types II and III were found mainly in limited conditions on TN 88-63 and Mouride cultivars, whereas nodules presenting the IGS type IV were collected only from cultivars B-21 and Mouride, in both water conditions. Strains corresponding to the different profiles were isolated. The phylogenetic analysis of 16S rRNA gene sequences showed that they belong to the genus, Bradyrhizobium. The sequence analysis of 16S-23S rDNA IGS revealed that the strains exhibiting IGS types II, III and IV were closely related to some Faidherbia albida isolates from Senegal. IGS type II can be assigned with at least 98% similarity to Bradyrhizobium genospecies IV. IGS types III and IV showed more than 96% similarity with genospecies VII and could belong to the same genospecies. IGS type I, the most frequent, exhibits low IGS similarity with reported sequences in the databases, and could represent a new genospecies.

 

Key words: BradyrhizobiumVigna unguiculata, water-limited condition, PCR-RFLP, 16S rDNA, 16S-23S rDNA IGS.