Although in another study [9] none of the isolates examined showed similarity with B. japonicum and B. liaoningense [9], sequence 146 in this study was closely related to B. japonicum USDA 38 (AF208514). Conclusion We have shown here that i) cowpea is strongly dependent on N2 fixation for its N nutrition in South Africa, Ghana and Botswana, ii) the diversity

of cowpea-nodulating bradyrhizobia was much higher in South Africa compared to Botswana and Ghana, iii) some strains from Southern Africa were phylogenetically very distinct, thus suggesting that they may be a new Bradyrhizobium species. Strain IGS type symbiotic efficiency was assessed for the first time in this study, and the data showed significant differences between and among the IGS types in terms

of their symbiotic efficiency. Acknowledgements This study was supported with funds from Tanespimycin concentration the McKnight Foundation to the South Africa Legumes Project, the National Research Foundation and the South African Research Chair in Agrochemurgy and Plant Symbioses to FDD, as well as a travel grant from the Organisation for the Prohibition of Chemical Weapons (OPCW) in The Netherlands to FPM. The NRF and TUT bursaries to FPM and AKB are also acknowledged. FPM is on study leave from the Botswana College of Agriculture (University of Botswana). References 1. Belane AK, Dakora FD: Measurement of N 2 fixation in 30 cowpea ( Vigna unguiculata L. Walp.) genotypes under field conditions in Ghana using 15 N natural abundance technique. Buparlisib cell line Symbiosis 2009, 48:47–57.CrossRef 2. Mpepereki S, Wollum AG, Makonese F: Diversity in symbiotic specificity of cowpea rhizobia indigenous to Zimbabwean soil. Plant Soil 1996, 186:167–171.CrossRef 3. Pule-Meulenberg F, Dakora FD: Assessing the symbiotic dependency of grain and tree legumes in N 2 fixation for their N nutrition in five agro-ecological zones of Botswana. Symbiosis 2009, 48:68–77.CrossRef 4. Naab JB, Chimphango SMB, Dakora FD: N 2 fixation in cowpea plants grown in farmers’ fields in the Upper Selleckchem Gemcitabine West Region of Ghana, measured using 15 N natural abundance. Symbiosis 2009, 48:37–46.CrossRef 5. Makoi JHJR, Chimphango SMB, Dakora FD: Effect of legume plant density

and mixed culture on symbiotic N 2 fixation in five cowpea ( Vigna unguiculata L. Walp.) genotypes in South Africa. Symbiosis 2009, 48:57–67.CrossRef 6. Law IJ, Botha WF, Majaule UC, Phalane FL: Symbiotic and genomic diversity of ‘cowpea’ bradyrhizobia from soils in Botswana and South Africa. Biol Fert Soils 2007, 43:653–663.CrossRef 7. Zhang WT, Yang JK, Yuan TY, Zhou JC: Genetic diversity and phylogeny of indigenous rhizobia from cowpea ( Vigna unguiculata (L.) Walp). 8. Steenkamp ET, Stepkowski T, Przymusiak A, Botha WJ, Law IJ: Cowpea and peanut in southern Africa are nodulated by diverse Bradyrhizobium strains harbouring genes that belong to the large pantropical clade common in Africa. Mol Phylogenet Evol 2008, 48:1131–1144.PubMedCrossRef 9.