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

, a leguminous tree native to the dry woodlands of Southern Africa, provides valuable timber, but is threatened by land conversion and overharvesting while showing limited natural regeneration. Nitrogen-fixing root nodule symbionts that could improve establishment of young seedlings have not yet been described. Therefore, we investigated the ability of to form nodules with a diverse range of rhizobia. In drought-prone areas under climate change with higher temperatures, inoculants that are heat-tolerant and adapted to these conditions are likely to be of advantage. Sources of bacterial isolates were roots of from nurseries in the Kavango region, other shrubs from this area growing near such as , , sp., or shrubs from drought-prone areas in Namaqualand (, ) or Kalahari (). Only slight protrusions were observed on roots, from which a non-nodulating sp. was isolated. Rhizobia that were isolated from nodules of other shrubs were affiliated to WR4, spp. (WR23/WR74/WR93/WR96), or (WR41/WR52). As many plant growth-promoting rhizobacteria (PGPR), nodule isolates produced siderophores and solubilized phosphate. Among them, only the strains nodulated under controlled conditions in the laboratory. Isolates were further characterized by multilocus sequence analysis and were found to be distant from known species. Among additional reference species tested for nodulation on , 7-2 and 5-10 from the Kavango region of Namibia as well as LMG6234 and LMG21728 induced nitrogen-fixing nodules, while USDA110 and SEMIA6148 did not. This suggests a broad microsymbiont range from and lineages. Phylogenetic analysis of genes indicated that nodulating bradyrhizobia did not belong to a specific symbiovar. Also, for and , nodule isolates WR4 or sp. WR52, respectively, were authenticated. Characterization of symbionts inducing effective root nodules in and other shrubs from Subsahara Africa (SSA) give insights in their symbiotic partners for the first time and might help in future to develop bioinoculants for young seedlings in nurseries, and for reforestation efforts in Southern Africa.