Population Levels of Indigenous Bradyrhizobia Nodulating Promiscuous Soybean in two Kenyan Soils of the Semi-arid and Semi-humid Agroecological Zones

Soybeans grown in Africa have been selected to nodulate effectively with indigenous Bradyrhizobium spp. populations since Bradyrhizobium japonicum populations are con-sidered absent or in very low numbers in African soils. The major objective of this study was to estimate total population of Bradyrhizobia specific to soybean in two agro-ecologically different study sites, Kiboko in Makueni District, Southeast Kenya (semi-arid to arid conditions) and Kaguru in Meru District, East Kenya (semi-humid climate). The population of the indigenous rhizobia specific to soybeans was deter-mined using the Most Probable Number (MPN) plant infection technique. In these experiments, the total Bradyrhizobia populations, the population sizes of taxonomi-cally defined slow-growing Bradyrhizobia specific to soybean and the population sizes of Bradyrhizobia spp. specific to tropical Glycine Cross (TGx) varieties were determined for the two study sites. Cowpea, Vigna unguiculata, cultivar Ken Kunde I was used to estimate the total Bradyrhizobia spp. population. Clark soybean, Glycine max, was used to estimate the population sizes of taxonomically defined slow-growing Bradyrhi