Date Published: July 01, 2018
Author(s): Samuel Mathu Ndungu, Monika M. Messmer, Dominik Ziegler, Hannes A. Gamper, Éva Mészáros, Moses Thuita, Bernard Vanlauwe, Emmanuel Frossard, Cécile Thonar.
•Bradyrhizobial root nodule symbionts of cowpea (Vigna unguiculata L. Walp) are diverse and widespread.•Soil texture and pH seem to influence the occurrence and abundance of the different bradyrhizobial root nodule symbionts of cowpea.•MALDI-TOF MS protein mass profiling of rhizobial isolates provides higher resolution than 16S rRNA gene sequencing.
Cowpea (Vigna unguiculata L. Walp) is an important food legume and an essential component of sustainable cropping systems in the sub humid tropics and, generaly, dry regions across the globe (Singh et al., 2002). In Kenya, it is grown in the drier eastern area around Mbeere, as well as, in the humid coastal area around Kilifi, where it makes up an important part of the diet of small-scale farmers (Kimiti et al., 2009).
This study showed that there are virtually no differences between the root nodule-colonising rhizobial communities of cowpea between contrasting agro-ecological regions and cultivated and uncultivated sites in Kenya including reference strains CBA from Biofix inoculant produced in Kenya and BK1 isolated from cowpea cultivated in soil from Burkina Faso. However, the richness of cowpea nodule symbionts was found to be high at each individual site. This may relate to the considerable promiscuity of cowpea for several different species of the genus Bradyrhizobium as well as, an apparent widespread distribution of the dominant symbionts. Yet more different and also some unique, but rare rhizobia, were found in the drier in- and upland agro-ecological region than the humid, coastland region and at uncultivated, compared to cultivated sites. We speculate that this may be explained by reduced protozoan predation in drier soils and higher plant species richness in the vegetation cover of uncultivated sites. Unlike geography, soil texture and pH influenced the occurrence and abundance of the resolved bradyrhizobial groups, pointing at a possibility to find suitable rhizobial inoculants for cowpea at sites with different soils to lower the dependence on mineral N fertilizer in efforts to maintain soil fertility and crop productivity.