The response of cowpea [Vigna unguiculata (Walp. (L.)] to inoculation with symbiotic microorganisms (arbuscular mycorrhizal fungus and rhizobium) was investigated on cultivated vertisoils (known locally as Dek) and arenosoils (known locally as Dior) in three geographic sites in Senegal. On the basis of soil physico-chemical characteristics, of most probable number (MPN) of indigenous rhizobia and of yields, a hierarchical analysis showed that the sites were grouped in three clusters. Some soils initially considered as Dek were grouped with Dior, so that all of Dior soils were grouped in the same cluster. No significant increasing in shoot biomass or yield was observed when cowpea was inoculated with fungi alone, whatever soil type. However, a significant or noticeable improvement in cowpea seeds production was obtained by rhizobium inoculation. It appeared that cowpea response to inoculation depended on geographical site and were often observed in sandy arenosoils (Dior type) or in loamy sand vertisoils (Dek type) with at least 15mgkg -1 of available phosphorus level.

The objective of this study was to characterize the diversity of arbuscular mycorrhizal fungal (AMF) communities colonizing the roots of Vigna unguiculata (L.) plants cultivated in two different sites in Senegal. Roots of cowpea plants and soil samples were collected from two fields (Ngothie and Diokoul) in the rural community of Dya (Senegal). Microscopic observations of the stained roots indicated a high colonization rate in roots from Ngothie site as compared to those from Diokoul site. The partial small subunit of ribosomal DNA genes was amplified from the genomic DNA extracted from these roots by polymerase chain reaction (PCR) with the universal primer NS31 and a fungal-specific primer AML2. Nucleotide sequence analysis revealed that 22 sequences from Ngothie site and only four sequences from Diokoul site were close to those of known arbuscular mycorrhizal fungi. Also, 47.6% of the clones from Ngothie site and 89.47% from Diokoul site were not close to known AMF. A total of 15 operational taxonomic units (OUT) were identified. Phylogenetic analyses showed that these clones belonged to the genera Glomus, Sclerocystis, Rhizophagus, Scutellospora, Gigaspora, Racocetra, Acaulospora and Redeckera. The genus Glomus is the most represented with six OTU, representing 40% of all OTU.