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• Several landraces of bambara groundnut (Vigna subterannea (L.) Verdc) exist in South Africa which are but, the most underutilized and un-researched legumes. • There is variations in the bambara groundnut landraces to the nodulation responses to a given species of rhizobium. • Bambara groundnut have promiscuous nodulation properties with different rhizobia species and host specificity rule does not apply for these legumes. • Bambara groundnut exhibit more symbiotic interaction with Rhizobia species belonging to the cowpea miscellany group. Bambara groundnut (Vigna subterranea) is one of the most underutilized and neglected legume crop used for human consumption worldwide. Unlike the common food and forage legumes, the symbiotic properties of this legume have not been studied sufficiently. This study is designed to investigate the nodulation compatibility and symbiotic performance of twelve landraces of V. subterranea with five different Rhizobia species isolated from the nodules of other legumes under glasshouse conditions. Pre-germinated seeds of each landrace planted in sterile river sand medium were inoculated with 108 cfu/ml of each rhizobium inoculum suspension and monitored with regular watering using nitrogen free Hoagland's solution for six weeks. The taxonomy and phylogeny of the five rhizobia species was determined using nucleotide sequence analysis of the 16S rRNA and recA (DNA recombination protein) genes. A concatenated multiple sequence alignment was used to construct an MLSA tree to further analyze the phylogeny of the strains. Significant differences were observed among individual bambara genotypes and rhizobia strains in terms of nodule numbers and dry weight, as well as plant biomass. Statistical analysis showed that Rhizobia strains XBD2 and XS34 identified as Bradyrhizobium zhangiangens and B. centrosematis respectively exhibited the highest nodulation compatibility in terms of nodule number and nodule dry weight with one or more bambara groundnut landraces. This study demonstrated that V. subterannea does not show preference to unique rhizobia, confirming that they are promiscuously nodulated by more than one species of rhizobium belonging mainly to the cowpea miscellany cross inoculation group. The findings of this study also provide insights into the selection and development of appropriate low cost rhizobia inoculants in the sustainable production of this underutilized legume for use by smallholder farmers in South Africa. [ABSTRACT FROM AUTHOR]

Pigeonpea (Cajanus cajan (L.) Millsp.) is an important grain legume, which, like several other legumes, depends on the process of biological nitrogen fixation for its nitrogen (N2) requirement by forming a symbiotic association with rhizobia. Compared to other tropical legumes, however, the productivity of pigeonpea in South Africa is low, despite the extensive interests in developing it for wider markets. To assist this process, the objectives of the current study were to (i) characterize putative indigenous rhizobial strains that were previously derived from local soils with no previous history of legume cultivation and (ii) confirm their nodulation abilities on a local landrace and a genetically improved (exotic) genotype of pigeonpea. DNA-based analyses using the 16S rRNA and recA genes showed that the strains predominantly represented Rhizobium and Bradyrhizobium, although we also recovered Phyllobacterium and Paraburkholderia. These rhizobia nodulated both the local landrace and the improved pigeonpea genotype that were included for comparative purposes. In many cases, rhizobia performed similarly on the two genotypes, although the locally sourced landrace mostly performed better in terms of nodulation and plant biomass. While the current study generated vital information regarding the diversity of indigenous rhizobia associating with pigeonpea, further screening (including field inoculation trials) would be necessary to identify possible elite nitrogen fixing rhizobial strains for development as inoculants to enhance South African pigeonpea production. [ABSTRACT FROM AUTHOR]

The cultivation of chickpea (Cicer arietinum L.) in South Africa is dependent on the application of suitable Mesorhizobium inoculants. Therefore, we evaluated the symbiotic effectiveness of several Mesorhizobium strains with different chickpea genotypes under controlled conditions. The tested parameters included shoot dry weight (SDW), nodule fresh weight (NFW), plant height, relative symbiotic effectiveness (RSE) on the plant as well as indole acetic acid (IAA) production and phosphate solubilization on the rhizobia. Twenty-one Mesorhizobium strains and six desi chickpea genotypes were laid out in a completely randomized design (CRD) with three replicates in a glasshouse pot experiment. The factors, chickpea genotype and Mesorhizobium strain, had significant effects on the measured parameters (p < 0.001) but lacked significant interactions based on the analysis of variance (ANOVA). The light variety desi genotype outperformed the other chickpea genotypes on all tested parameters. In general, inoculation with strains LMG15046, CC1192, XAP4, XAP10, and LMG14989 performed best for all the tested parameters. All the strains were able to produce IAA and solubilize phosphate except the South African field isolates, which could not solubilize phosphate. Taken together, inoculation with compatible Mesorhizobium promoted chickpea growth. This is the first study to report on chickpea-compatible Mesorhizobium strains isolated from uninoculated South African soils with no history of chickpea production; although, their plant growth promotion ability was poorer compared to some of the globally sourced strains. Since this study was conducted under controlled conditions, we recommend field studies to assess the performance of the five highlighted strains under environmental conditions in South Africa. [ABSTRACT FROM AUTHOR]

Legumes Lessertia diffusa and Calobota sericea, indigenous to South Africa, are commonly used as fodder crops with potential for sustainable livestock pasture production. Rhizobia were isolated from their root nodules grown in their respective soils from the Succulent Karoo biome (SKB) in South Africa, identified and characterized using a polyphasic approach. Sequence analysis of the 16S rRNA gene confirmed all isolates as Mesorhizobium members, which were categorized into two distinct lineages using five housekeeping protein-coding genes. Lineage I included 14 strains from both legumes, while Lineage II comprised a single isolate from C. sericea. Differences in phenotypic traits were observed between the lineages and corroborated by average nucleotide identity analyses. While all strains nodulated their original hosts, strains from C. sericea failed to effectively nodulate L. diffusa and vice versa. Phylogenetic analyses of nitrogen fixation (nifH) and nodulation (nodA, nodC) loci grouped all strains in a single clade, suggesting that unique symbiotic loci determine nodulation of these legumes. We designated Lineage I and II as Mesorhizobium salmacidum sp. nov. (Ld1326 Ts ; GCA&#95;037179605.1 Ts ) and Mesorhizobium argentiipisi sp. nov. (Cs1330R2N1 Ts ; GCA&#95;037179585.1 Ts ), using genome sequences as nomenclatural types according to the Nomenclatural Code for Prokaryotes using Sequence Data, thus avoiding complications with South Africa's biodiversity regulations. Identifying effective microsymbionts of L. diffusa and C. sericea is essential for conservation of Succulent Karoo Biome, where indigenous invasive species like Vachellia karroo and non-native Australian acacia species are present. Furthermore, targeted management practices using effective symbionts of the studied legumes can sustain the biome's socio-economic contribution through fodder provision., Competing Interests: Declarations. Conflict of interest: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Ethical approval: Not applicable., (© 2025. The Author(s).)

Twenty years ago, the first members of the genus Burkholderia capable of nodulating and fixing N2 during symbiosis with leguminous plants were reported. The discovery that β-proteobacteria could nodulate legumes represented a breakthrough event because, for over 100 years, it was thought that all rhizobia belonged exclusively to the α-Proteobacteria class. Over the past 20 years, efforts toward robust characterization of these bacteria with large-scale phylogenomic and taxonomic studies have led to the separation of clinically important and phytopathogenic members of Burkholderia from environmental ones, and the symbiotic nodulating species are now included in the genera Paraburkholderia and Trinickia. Paraburkholderia encompasses the vast majority of β-rhizobia and has been mostly found in South America and South Africa, presenting greater symbiotic affinity with native members of the families Mimosoideae and Papilionoideae, respectively. Being the main center of Mimosa spp. diversity, Brazil is also known as the center of symbiotic Paraburkholderia diversity. Of the 21 symbiotic Paraburkholderia species described to date, 11 have been isolated in Brazil, and others first isolated in different countries have also been found in this country. Additionally, besides the symbiotic N2-fixation capacity of some of its members, Paraburkholderia is considered rich in other beneficial interactions with plants and can promote growth through several direct and indirect mechanisms. Therefore, these bacteria can be considered biological resources employed as environmentally friendly alternatives that could reduce the agricultural dependence on agrochemical inputs. [ABSTRACT FROM AUTHOR]

Pigeonpea is an important grain legume. It contributes to the improvement of soil fertility through biological nitrogen (N) fixation. However, the symbiotic efficiency of pigeonpea with native soil rhizobia has not been determined adequately. This study was designed to determine the variation in the N fixation ability of pigeonpea inoculated with the native rhizobia. Forty soil samples were collected from diverse locations across South Africa and used for inoculating pigeonpea seed. Each pigeonpea genotype was inoculated separately with each soil sample and raised in a nitrogen-depleted growth medium in the greenhouse. A split-plot experimental design was used in the study. Several N fixation variables of pigeonpea were measured. There was >40.0% difference in the number of nodules between genotypes 'Ex-PP-MD-321' and 'Mpuma-B-Spot' but the nodule dry weight between the two genotypes was >80.0%. In contrast, the heaviest dry shoots (0.4513 g), weighed 52.0% heavier than those that were observed for 'Mpuma-B-Spot'. Pigeonpea showed differential N fixation ability with the nodules, suggesting that there was potential to select for optimum host × rhizobial isolate combinations for the process and to expand the production area of the crop. [ABSTRACT FROM AUTHOR]

Soils in the semi-arid regions such as north-eastern South Africa, where chickpea was recently introduced, are commonly characterized by poor fertility and low pH. Preliminary studies show that the crop has a huge potential in the region, but lack of nodulation has consistently been a problem. We assessed the response of soil pH and nodulation of three chickpea genotypes (ACC #4, ACC #5, and ACC #6) to biochar application (0, 10, and 20 t ha−1) and rhizobium inoculation (inoculated and uninoculated) in Thohoyandou (clay soil) and Nelspruit (loamy sand soil), South Africa in 2015 and 2016. Nodulation was assessed at flowering by determining the number of nodules per plant and nodule dry weight, and soil pH was analyzed after harvest in both seasons. Biochar increased pH by 0.7 (clay soils) and 0.7–0.8 (the more acidic loamy sand soils) pH units. Similarly, biochar increased nodulation in inoculated treatments in both locations and seasons, and this was mainly associated with the effect of biochar on soil pH. The increase in nodulation with inoculation varied amongst the genotypes. Clearly biochar and rhizobium inoculation may be crucial for improving soil pH and nodulation in chickpea cropping systems characterized by poor soils. [ABSTRACT FROM AUTHOR]

A major driving force behind sustainable agriculture and protection of the environment is effective management of nitrogen (N) in farming. Better understanding on the growth and functional adaptation of legumes under low nutrient savannah and grassland ecosystems remain crucial for food security. Therefore, this study examined if Vigna radiata (L.) R. Wilczek (Mung bean) establishes multiple symbiosis with soil microbes in KwaZulu-Natal (KZN) soils and how that symbiosis affects plant N nutrition and related-carbon growth costs. The study was conducted in the greenhouse using soils from four (Hluhluwe, Izingolweni, Bergville, and Ashburton) different geographical areas of KZN province. The soils were used as a natural inoculum and growth substrate thus treated as four treatments. Soil analysis of the four geographical areas showed marked differences with regard to phoshorus (P) and potassium (K) nutrient concentrations, exchange acidity and arbuscular mycorrhizal (AM) spore counts, while no significant differences were observed among the four treatments in term of N concentration and root colonization. Soils from the four sites were acidic and showed variation in nutrients especially with regard to P and N. Bergville soils had the highest P concentrations, exchange acidity and AM fungi spore counts, while Hluhluwe soils had the highest concentration of K, total cations and lowest spore count. Vigna radiata grown in Hluhluwe soils had higher biomass when compared to Bergville soil-grown plants. All plants nodulated with the exception of plants that were grown with Bergville soil. Despite differences in soil nutrient concentration, V. radiata plants established symbiosis with AM fungi, Rhizobium and numerous Bacillus species. Furthermore, the legume plants including the non-nodulated Bergville-grown V. radiata plants were able to switch N sources (atmospheric and soil N) to maintain their N nutrition and carbon construction costs. This observation suggests that non-nodulated Bergville-grown plants may have established symbiosis with other bacterial taxa such as Bacillus spp. and other endophytic bacterial spp. that fix atmospheric N. Overall, the symbiotic association of V. radiata with Rhizobium , AM fungi and various Bacillus species enhanced N utilization. In addition, V. radiata has the capacity to switch between soil N and atmospheric N while maintaining low carbon construction cost under low soil nutrient conditions. Vigna radiata thus can be adaptable to low soil nutrient savannah and grassland ecosystems in KZN province, South Africa. • Savannah and grassland soils are acidic and nutrient poor specifically with regard to N and P. • Vigna radiata formed symbiotic association with arbuscular mycorrhizal fungi, Rhizobium and Bacillus sp. • Legume–microbe symbiotic interaction enhanced V. radiata N nutrition and acquisition from the soil. • The interaction also maintained carbon construction costs under low nutrient soils. [ABSTRACT FROM AUTHOR]

Rhizobia is a group of gram-negative soil-borne bacteria with several beneficial strains for biological nitrogen fixation in legume crops. Rhizobium strains are found native in the soil but where they are absent, commercial strains are inoculated on crops. We assessed the availability of native rhizobia in chickpea fields at two sites, with contrasting soil types, in NE South Africa. Serial dilutions were used to identify bacteria from soil samples and chickpea nodules sampled before sowing and at flowering, respectively. Our results indicated the absence of rhizobia strains at both sites. Burkholderia cenocepacia, Klebsiella variicola, Bacillus subtilis and Ochrobactrum spp, which are not important in agriculture but are often reported in clinical environments, were identified. Therefore, inoculating chickpea with compatible rhizobia strains may be necessary in some soils in this region. [ABSTRACT FROM AUTHOR]

Rooibos tea, Aspalathus linearis (Burm.f.), represents one of South Africa's most important indigenous crops, and monotypic plantations are rapidly replacing wild populations. Dwindling wild rooibos populations may drastically reduce possible, but hitherto overlooked, natural resources to bolster commercial productivity and long-term sustainability. Here, using next generation sequencing data, we seek to determine whether cultivation impacts on the diversity and community structure of mutualistic nitrogen fixing bacteria (rhizobia) associated with rooibos plants. We do this by generating operational taxonomic units (OTUs) from nodulation ( nodC ) and nitrogenase ( nifH ) DNA sequence data from rhizobia within root nodules of rooibos plants from cultivated and wild populations. For these rhizobial communities we found significant differences for various OTU diversity metrics due to geography (site), the interaction between site and status (cultivated vs. wild), but not for status. We also sequenced nodC soil microbiomes and found evidence for compositional differences in soil rhizobial communities due to geography, status (cultivated vs. wild), and the interaction between geography and status. Our data adds to existing evidence suggesting that tea cultivation in South Africa may have limited impacts on soil microbial community diversity and structure, and that such changes are mainly driven by larger geographic processes rather than human-mediated disturbances such as cultivation. [ABSTRACT FROM AUTHOR]

Background and aims: The South African herbaceous legume species Lessertia capitata, L. diffusa, L. excisa L. incana and L. herbacea were introduced to Australia to assess plant establishment and survival, as well as the saprophytic ability of their root nodule bacteria (RNB). Methods: Five Lessertia spp., were inoculated with selected RNB strains and were sown in five different agroclimatic areas of the Western Australian wheat-belt during 2007 and 2008. Plant population and summer survival were evaluated in situ . Soil samples and nodules from host plants were also taken from each site. The re-isolated rhizobia were RPO1-PCR fingerprinted and their partial dnaK and nodA genes were sequenced to confirm their identity. Results: Plants achieved only poor establishment followed by weak summer survival. More than 83 % of the rhizobia re-isolated from Lessertia did not correlate with the original inoculants' fingerprints, and were identified as Rhizobium leguminosarum. The nodA sequences of the naturalised strains were also clustered with R. leguminosarum sequences, thus eliminating the likelihood of lateral gene transference from Mesorhizobium and suggesting a competition problem with indigenous rhizobia. Conclusion: The stressful soil conditions and high numbers of resident R. leguminosarum strains in Western Australian soils, and their ability to rapidly nodulate Lessertia spp. but not fix nitrogen are likely to preclude the adoption of Lessertia as an agricultural legume in this region. [ABSTRACT FROM AUTHOR]

Abstract: We investigated symbiotic and physiological properties, and taxonomic position, of 23 bacterial strains isolated from Lebeckia ambigua root nodules collected from the South African fynbos region. The capacity for nodulation and nitrogen fixation on three provenances of L. ambigua was investigated for these strains together with several physiological characters, including growth rate on peat and in betonite clay, survival on polyethylene beads and pH tolerance. Additionally, the 16S rRNA gene phylogeny was determined. The root nodule bacteria isolated clustered in five different groups belonging to the genus Burkholderia, most closely related to B. caledonica, B. graminis and B. tuberum. Moreover there was a very strong influence of collection site on the taxonomy of the Burkholderia strains. The physiological characterisation revealed two promising strains, WSM4174 and WSM4184, achieved rapid growth in normal media and reached high, stable numbers in sterile peat. However, there was a worrying susceptibility to desiccation amongst these Burkholderia. Additionally, evidence was found for isolation of non-symbiotic strains from the nodule material collected in South Africa. [Copyright &y& Elsevier]

[Display omitted] • Bradyrhizobium species isolated from diverse legumes in South Africa. • Delineation of these species following the genealogical concordance approach. • Novel Bradyrhizobium species represent nodA alleles specific to South African Clades. • Bradyrhizobium species may have agricultural importance in sub-Saharan Africa. Africa is known for its rich legume diversity with a significant number of endemic species originating in South Africa. Many of these legumes associate with rhizobial symbionts of the genus Bradyrhizobium , of which most represent new species. Yet, none of the Bradyrhizobium species from South Africa have been described. In this study, phylogenetic analysis of 16S rRNA gene sequences of fourteen strains isolated in southern Africa from root nodules of diverse legumes (i.e., from the tribes Crotalarieae, Acacieae, Genisteae, Phaseoleae and Cassieae) revealed that they belong to the Bradyrhizobium elkanii supergroup. The taxonomic position and possible novelty of these strains were further interrogated using genealogical concordance of five housekeeping genes (atpD, dnaK, glnII, gyrB and rpoB). These phylogenies consistently recovered four monophyletic groups and one singleton within Bradyrhizobium. Of these groups, two were conspecific with Bradyrhizobium brasilense UFLA 03-321T and Bradyrhizobium ivorense CI-1BT, while the remaining three represented novel taxa. Their existence was further supported with genome data, as well as metabolic and physiological traits. Analysis of nodA gene sequences further showed that the evolution of these bacteria likely involved adapting to local legume hosts and environmental conditions through the acquisition, via horizontal gene transfer, of optimal symbiotic loci. We accordingly propose the following names Bradyrhizobium acaciae sp. nov. 10BBT (SARCC 730T = LMG 31409T), Bradyrhizobium oropedii sp. nov. Pear76T (SARCC 731T = LMG 31408T), and Bradyrhizobium altum sp. nov. Pear77T (SARCC 754T = LMG 31407T) to accommodate three novel species, all of which are symbionts of legumes in South Africa. [ABSTRACT FROM AUTHOR]

Bradyrhizobium are N 2 -fixing microsymbionts of legumes with relevant applications in agricultural sustainability, and we investigated the phylogenetic relationships of conserved and symbiotic genes of 21 bradyrhizobial strains. The study included strains from Western Australia (WA), isolated from nodules of Glycine spp. the country is one genetic center for the genus and from nodules of other indigenous legumes grown in WA, and strains isolated from forage Glycine sp. grown in South Africa. The 16S rRNA phylogeny divided the strains in two superclades, of B. japonicum and B. elkanii , but with low discrimination among the species. The multilocus sequence analysis (MLSA) with four protein-coding housekeeping genes (dnaK , glnII , gyrB and recA) pointed out seven groups as putative new species, two within the B. japonicum , and five within the B. elkanii superclades. The remaining eleven strains showed higher similarity with six species, B. lupini , B. liaoningense , B. yuanmingense , B. subterraneum , B. brasilense and B. retamae. Phylogenetic analysis of the nodC symbiotic gene clustered 13 strains in three different symbiovars (sv. vignae, sv. genistearum and sv. retamae), while seven others might compose new symbiovars. The genetic profiles of the strains evaluated by BOX-PCR revealed high intra- and interspecific diversity. The results point out the high level of diversity still to be explored within the Bradyrhizobium genus, and further studies might confirm new species and symbiovars. [ABSTRACT FROM AUTHOR]