To increase the threshold of cowpea yields in Africa would require identification of genotypes that exhibit high symbiotic performance and better plant growth. Because cowpea nodulates freely

with both rhizobia and bradyrhizobia [1], it is often described as being promiscuous. Yet only few studies [1, 6–9] have examined the biodiversity of cowpea rhizobia and bradyrhizobia in Africa, the native home of this legume species. One study [6] reported four different Bradyrhizobium strains belonging to 3 genospecies, and concluded that the cowpea rhizobia appeared to be more diverse in arid areas. Recently, another study [8] grouped cowpea rhizobia from China into six genospecies, and linked microsymbiont distribution and diversity MG-132 mw to geographical location. Like most published reports on the biodiversity of selleck compound root-nodule bacteria, namely rhizobia,

bradyrhizobia, azorhizobia, sinorhizobia and mesorhizobia, none of the studies [1, 6–9] on cowpea rhizobia and bradyrhizobia has assessed the linkage between symbiotic functioning and bacterial IGS types resident in nodules and/or used for determining rhizobial biodiversity. Quantifying N2 fixation in legumes and linking amounts of N-fixed to the IGS types found in their root nodules, could provide some indication of the symbiotic efficiency of resident bacterial populations used for establishing rhizobial biodiversity. That way, studies of legume agronomy in the context of N contribution could add value to bacterial biodiversity and phylogeny in relation to symbiotic functioning. In this study, 9 cowpea genotypes were planted in field experiments in Botswana, South Africa and Ghana with the aim of i) trapping indigenous cowpea rhizobia in the 3 countries for isolation and molecular characterisation, ii) quantifying N-fixed in the cowpea

genotypes using the 15N natural abundance Methane monooxygenase technique, and iii) relating the levels of nodule functioning (i.e. N-fixed) to the IGS types found inside cowpea nodules, in order to assess strain IGS type symbiotic efficiency. Methods Experimental site descriptions In Ghana, the experiments were conducted at the Savanna Agricultural Research Institute (SARI) site at Dokpong, Wa, in 2005. The site is located in the Guinea savanna, (latitude 10° 03′ N, longitude 2° 30′ W, and altitude 370 m) and has a unimodal rainfall (1100 mm annual mean) that starts in May and ends in September/October. The soils are classified as Ferric Luvisols [10]. Prior to experimentation, the site had been fallowed for 3 years. In South Africa, the Agricultural Research Ricolinostat Council (ARC-Grain Crop Research Institute) farm at Taung, Potchefstroom, was used for the field trials. The Taung experimental site is located between latitudes 27° 30′ S and longitudes 24° 30′ E, and is situated in the grassland savanna with a unimodal rainfall (1061 mm annual mean) that begins in October and lasts until June/July the following year.