Root-Nodule Bacteria of Legumes Growing in Semi-Arid African Soils and Other Areas of the World

Abstract

In Africa, arid and semi-arid soils are characterized by a diverse occurrence of plants including nodulated legumes which are adapted to the prevailing and often harsh environmental conditions. Such soils also harbour a large diversity of indigenous rhizobial symbionts (comparable to legume diversity) and other bacterial endophytes that have a potential to be developed into elite strains to be used as inoculum. However, very few studies have investigated the diversity of root-nodule bacteria on African soils, the main reason being that funds for research are often lacking. Discoveries of new rhizobial species are to be expected from different soil ecologies that are likely to be inhabited by various types of microorganisms. It is concluded that the semi-arid and arid African soils have rhizobia that is possibly as equally diverse as their host legumes. Research in these areas is likely to find novel species with a great potential for use in agricultural systems.

Diversity of Bradyrhizobia in Subsahara Africa: A Rich Resource

“…Among Leguminosae / Fabaceae , roughly 1,500 were yet alone considered in Southern Africa (Trytsman et al, 2016 ). SSA being the center of origin for many legumes, these regions might entail a high diversity of effective microsymbionts (Pule-Meulenberg, 2014 ). The full potential of SSA indigenous legumes may not yet have been recognized, although they can be predicted as valuable germbank for possible agricultural use in arid and semi-arid regions (Sprent et al, 2010 ).…”

“…The increased number of bradyrhizobial species allowed several studies to uncover a geographic distribution. Most of our knowledge about rhizobia and their biogeography is based on studies conducted in Asia, Europe and the Americas (Pule-Meulenberg, 2014 ). Information on SSA rhizobia is limited despite SSA regions presumably entail a high microsymbiont diversity that is favored by at least three factors: First, SSA is characterized by heterogeneous soils and climates, providing diverse habitats (Petersen et al, 2010 ; Gröngröft et al, 2013 ; Wade et al, 2014 ).…”

“…It has been suggested that the selection pressure on rhizobia may lead to the evolution of stress tolerant strains which could partly explain the increased diversity observed in water limited environments. Third, Africa is the center of origin of many legumes (including cowpea and Bambara groundnut) and a rich diversity of wild legume species exists (Pule-Meulenberg, 2014 ; Lemaire et al, 2015 ).…”

“…Apart from the geographic location, this observation might be related to the natural selectivity of the sampled legume hosts and the lack of taxonomic studies. Relatively few studies focused on natural microsymbionts of cowpea and especially Bambara groundnut (Pule-Meulenberg, 2014 ; Puozaa et al, 2017 ). The first validly published species from this host, B. subterraneum (Grönemeyer et al, 2015a ) was mainly isolated from Bambara groundnut, and also from peanut.…”

Root Nodule Rhizobia From Undomesticated Shrubs of the Dry Woodlands of Southern Africa Can Nodulate Angolan Teak Pterocarpus angolensis, an Important Source of Timber

“…The key mineral nutrients N and P are in very low concentrations, for example, in sandy soils of Northern Namibia ( Gröngröft et al, 2013 ). In-depth knowledge on rhizobial symbionts in Subsahara Africa is still limited ( Grönemeyer and Reinhold-Hurek, 2018 ), although Africa is a center of origin of many legumes (e.g., cowpea and Bambara groundnut), and offers a rich diversity of wild legume species ( Sprent et al, 2010 ; Pule-Meulenberg, 2014 ; Lemaire et al, 2015a ). Thus, the diversity of Bradyrhizobium species in Subsahara Africa may be as yet underestimated and represents a hidden rich resource for inoculant development in future ( Grönemeyer and Reinhold-Hurek, 2018 ).…”