A survey for plant-growth-promoting rhizo-bacteria and symbionts associated with crop plants in the Okavango region of Southern Africa

The predominant agriculture paradigm based on improved varieties of common staple crops in high-input systems has not succeeded addressing food insecurity and malnutrition e.g. in Sub-Saharan Africa (Rudebjer et al. 2013), where over 200 million people (28% of the population) were undernourished in 2005-2007 (FAO, 2010)).Yield variability and risk for crop failure in Africa's rainfed agriculture systems contribute to factors that explain difficulties in adopting new technologies (Ogada et al. 2010).These risks are predicted to increase in many areas in Southern Africa due to climate change, as projections suggest a decline in land area suitable for cultivation of crops (Lane & Jarvis 2007).On the other hand, demand for staple crops like maize is currently increasing in Africa due to changes in eating habits, with limited production and increasing imports.Abstract: Regions in the Okavango catchment and delta such as highlands ofAngola, the Kavango region of Namibia, and the Okavango Delta region of Botswana, although rich in plant diversity and density, have not produced significant yields when cropped by small scale farmers in the region.This phenomenon may be due to many factors among which is low nitrogen and other crop nutrients availability.This region due to its richness in flora may harbour bacteria which play a major role in plant nutrient availability.However, some of these rhizobacteria can be isolated and re-inoculated on crop plants to improve crop yields.Thus a survey on root nodulation of local pulses such as Vigna unguiculata, V. subterranea, and Phaseolus vulgaris, in the Chitembo area of Angola and the Kavango region of Namibia was carried out.Nodulated plants and putatively symbiotic bacteria were detected from a range of sites for all species.In Namibia, isolation of putative plant-growth-promoting rhizobacteria (PGPRs) was done on cereal crops and from other indigenous plants on farmland and from pristine areas.In Botswana, phosphate solubilizing bacteria were isolated from the roots of grasses in the floodplains and assayed for their ability to solubilize soil phosphate with the intention of using them to increase yields in sorghum (Sorghum vulgare).In total, 46 bacterial strains were isolated from nodules of legumes from Namibia, while 37 strains were isolated from Angola.Additionally, 32 strains of plant associated rhizobacteria were obtained from cereals or natural plants from the Kavango region in Namibia, and further ten isolates were selected from the Seronga region in Botswana.The large number of bacteria generated by this survey may contain some bacteria that may promote plant growth and improve soil fertility.