Morphophysiological diversity of rhizobia nodulating pigeon pea (Cajanus cajan L. Millsp.) growing in Ethiopia

Pigeon pea (Cajanus cajan (L.) Millsp.) is an important protein source grown in several tropical and subtropical countries, and is considered a multi-purpose plant that is resistant to the conditions where drought and salinity is a common phenomenon. The aim of this study was to evaluate the diversity of rhizobial isolates obtained from root nodules of pigeon pea plants grown in central and southern Ethiopia. A total of 116 nitrogen-fixing rhizobial strains were isolated. The bacterial isolates were characterized by 91 phenotypic traits including cultural characteristics, intrinsic antibiotic and heavy metal resistance, salt, pH and incubation temperature tolerance, and carbon and nitrogen sources utilization ability. Preliminary symbiotic properties of the isolates were also evaluated. The isolates were compared with seven reference strains of rhizobia by application of the unweighted pair group method with arithmetic means (UPGMA) using NTSYSpc Version 2.1 software program. The dendrogram constructed from cluster analysis of 91 phenotypic traits, grouped them into six clusters and eight un-clustered positions at 80% relative similarity. Cluster I contained 83% of the test isolates that were grouped together with the reference strains Bradyrhizobium japonicum (HAMBI 2314T) and Bradyrhizobium elkanii (LMG 6164), suggesting that pigeon pea is commonly nodulated by bradyrhizobia. Results from symbiotic effectiveness test revealed that majority of the isolates were found to be effective. Generally, this investigation demonstrated that rhizobial population nodulating C. cajan on the study area were phenotypically diverse and symbiotically effective. Furthermore, the result indicates the existence of strains in the collection, which can tolerate environmental stresses, thus can be developed into inoculant for pigeon pea inoculation and production in Ethiopia and beyond

Phylogeography and Symbiotic Effectiveness of Rhizobia Nodulating Chickpea (Cicer arietinum L.) in Ethiopia

Chickpea (Cicer arietinum L.) used to be considered a restrictive host that nodulated and fixed nitrogen only with Mesorhizobium ciceri and M.mediterraneum. Recent analysis revealed that chickpea can also establish effective symbioseswith strains of several other Mesorhizobium species such as M. loti, M. haukuii, M. amorphae, M. muleiense, etc. These strains vary in their nitrogen fixation potential inviting further exploration. We characterized newly collected mesorhizobial strains isolated from various locations in Ethiopia to evaluate genetic diversity, biogeographic structure and symbiotic effectiveness. Symbiotic effectiveness was evaluated in Leonard Jars using a locally released chickpea cultivar “Nattoli”. Most of the new isolates belonged to a clade related to M. plurifarium, with very few sequence differences, while the total collection of strains contained three additional mesorhizobial genospecies associated with M. ciceri, M. abyssinicae and an unidentified Mesorhizobium species isolated from a wild host in Eritrea. The four genospecies identified represented a subset of the eight major Mesorhizobium clades recently reported for Ethiopia based on metagenomic data. All Ethiopian strains had nearly identical symbiotic genes that grouped them in a single cluster with M. ciceri, M. mediterraneum and M. muleiense, but not with M. plurifarium. Some phylogeographic structure was observed, with elevation and geography explaining some of the genetic differences among strains, but the relation between genetic identity and symbiotic effectiveness was observed to be weak

Symbiotic interactions between chickpea (Cicer arietinum L.) genotypes and Mesorhizobium strains

Legume genotype (GL) x rhizobium genotype (GR) interaction in chickpea was studied using a genetically diverse set of accessions and rhizobium strains in modified Leonard Jars. A subset of effective GL x GR combinations was subsequently evaluated in a pot experiment to identify combinations of chickpea genotypes and rhizobium strains with stable and superior symbiotic performance. A linear mixed model was employed to analyse the occurrence of GL x GR interaction and an additive main effects and multiplicative interaction (AMMI) model was used to study patterns in the performance of genotype-strain combinations.We found statistically significant interaction in jars in terms of symbiotic effectiveness that was entirely due to the inclusion of one of the genotypes, ICC6263. No interaction was found in a subsequent pot experiment. The presence of two genetic groups (Kabuli and Desi genepools) did not affect interaction with Mesorhizobium strains. With the exception of a negative interaction with genotype ICC6263 in the jar experiment, the type strain Mesorhizobium ciceri LMG 14989 outperformed or equalled other strains on all chickpea genotypes in both jar and pot experiments. Similar to earlier reports in common bean, our results suggest that efforts to findmore effective strains may be more rewarding than aiming for identification of superior combinations of strains and genotypes

Groundnut (Arachis hypogaea L.) and cowpea (Vigna unguiculata L. Walp) growing in Ethiopia are nodulated by diverse rhizobia

A total of eighty one (81) rhizobial isolates were recovered from root nodules of cowpea (Vigna unguiculata L. Walp.) and groundnut (Arachis hypogaea L.) grown in soils collected from eight different sites (Hawassa, Wondogenet, Chofa, Badawacho, Bodity, Gofa, Ziway, and Alemtena) in Ethiopia with no known history of inoculation. The test isolates together with seven reference strains belonging to five genera including Rhizobium, Ensifer, Mesorhizobium, Bradyrhizobium and Azorhizobium were characterized using ninety phenotypic traits. Thirty one isolates (38%) were found to be fast growers while fifty isolates (62%) were slow growers. The majority of the isolates showed an intrinsic resistance to antibiotics (μg/ml), Chloramphenicol (5 and 15), Lincomycin (100), Novobiocin (0.5 and 1.5), and Erythromycin (10 and 20) and to heavy metals manganese sulphate (500) and copper chloride (100). Most isolates did not tolerate NaCl concentration >3% (w/v) and high temperature (45°C). Dendrogram was constructed by applying the unweighted pair group method with arithmetic means (UPGMA) using NTSYSpc Version 2.1. They were grouped into seven clusters and eight unclustered positions, when 82% relative similarity was used as a cut point. Fifty eight percent of the test isolates were grouped with Bradyrhizobium japonicum and Bradyrhizobium elkanii superclades, thus indicating that rhizobia nodulating cowpea and groundnut are delineated within a branch that defines Bradyrhizobium genus. To elucidate the precise taxonomic positions of the isolates, further genetic studies are required using modern molecular biological methods

Phenotypic Characteristics and Preliminary Symbiotic Effectiveness of Rhizobia Associated with Haricot Bean Growing in Diverse Locations of Southern Ethiopia

Phenotypic characteristics of one hundred thirteen rhizobia nodulating haricot bean (Phaseolus vulgaris L.) growing on soils of nine different locations from southern Ethiopia were studied. Their tolerance to varying temperature, salinity, soil pH, heavy metals, antibiotics, their symbiotic effectiveness and cultural characteristics were determined. Eight reference species belonging to four different genera were also included in the analyses. The analyses allowed the description of a wide physiological diversity among tested isolates. Numerical analysis, based on numerical taxonomic approach, of the phenotypic characteristics, using Unweighted Pair Group Method with Average algorithm as implemented in NTSYspc21 software package, showed that, the tested isolates fell into five major diversity groups (designated as group I-V), when 82% level of relative similarity were used as cut-off point. Four strains were found to occupy a separate branch, thus designated as U (unclustered) group. While strains belonging to groups 1-IV were found to associate with recognized species belonging to Rhizobium, Ensifer and Mesorhizobium genus, the remaining test strains in cluster V and U were found to occupy distinct branches of their own on the dendrogram. Under laboratory condition, they were able to grow at pH ranging from 4 to 10.5; majority tolerated salt concentration (0.5-1%) and grew at a maximum temperature between 35 and 40 °C. The isolates were able to utilize a wide range of carbon and amino acid source and tolerated range of antibiotics and heavy metals. Based on the symbiotic effectiveness test, a number of potential isolates have been identified for inoculation trials

Consistency, variability, and predictability of on-farm nutrient responses in four grain legumes across east and west Africa

Open Access Article; Published online: 26 May 2023Grain legumes are key components of sustainable production systems in sub-Saharan Africa, but wide-spread nutrient deficiencies severely restrict yields. Whereas legumes can meet a large part of their nitrogen (N) requirement through symbiosis with N2-fixing bacteria, elements such as phosphorus (P), potassium (K) and secondary and micronutrients may still be limiting and require supplementation. Responses to P are generally strong but variable, while evidence for other nutrients tends to show weak or highly localised effects. Here we present the results of a joint statistical analysis of a series of on-farm nutrient addition trials, implemented across four legumes in four countries over two years. Linear mixed models were used to quantify both mean nutrient responses and their variability, followed by a random forest analysis to determine the extent to which such variability can be explained or predicted by geographic, environmental or farm survey data. Legume response to P was indeed variable, but consistently positive and we predicted application to be profitable for 67% of farms in any given year, based on prevailing input costs and grain prices. Other nutrients did not show significant mean effects, but considerable response variation was found. This response heterogeneity was mostly associated with local or temporary factors and could not be explained or predicted by spatial, biophysical or management factors. An exception was K response, which displayed appreciable spatial variation that could be partly accounted for by spatial and environmental covariables. While of apparent relevance for targeted recommendations, the minor amplitude of expected response, the large proportion of unexplained variation and the unreliability of the predicted spatial patterns suggests that such data-driven targeting is unlikely to be effective with current data

Characterization of the natural variation in Arabidopsis thaliana metabolome by the analysis of metabolic distance

Metabolite fingerprinting is widely used to unravel the chemical characteristics of biological samples. Multivariate data analysis and other statistical tools are subsequently used to analyze and visualize the plasticity of the metabolome and/or the relationship between those samples. However, there are limitations to these approaches for example because of the multi-dimensionality of the data that makes interpretation of the data obtained from untargeted analysis almost impossible for an average human being. These limitations make the biological information that is of prime importance in untargeted studies be partially exploited. Even in the case of full exploitation, current methods for relationship elucidation focus mainly on between groups variation and differences. Therefore, a measure that is capable of exploiting both between- and within-group biological variation would be of great value. Here, we examined the natural variation in the metabolome of nine Arabidopsis thaliana accessions grown under various environmental conditions and established a measure for the metabolic distance between accessions and across environments. This data analysis approach shows that there is just a minor correlation between genetic and metabolic diversity of the nine accessions. On the other hand, it delivers so far in Arabidopsis unexplored chemical information and is shown to be biologically relevant for resistance studies

Bacteria-inducing legume nodules involved in the improvement of plant growth, health and nutrition

Bacteria-inducing legume nodules are known as rhizobia and belong to the class Alphaproteobacteria and Betaproteobacteria. They promote the growth and nutrition of their respective legume hosts through atmospheric nitrogen fixation which takes place in the nodules induced in their roots or stems. In addition, rhizobia have other plant growth-promoting mechanisms, mainly solubilization of phosphate and production of indoleacetic acid, ACC deaminase and siderophores. Some of these mechanisms have been reported for strains of rhizobia which are also able to promote the growth of several nonlegumes, such as cereals, oilseeds and vegetables. Less studied are the mechanisms that have the rhizobia to promote the plant health; however, these bacteria are able to exert biocontrol of some phytopathogens and to induce the plant resistance. In this chapter, we revised the available data about the ability of the legume nodule-inducing bacteria for improving the plant growth, health and nutrition of both legumes and nonlegumes. These data showed that rhizobia meet all the requirements of sustainable agriculture to be used as bio-inoculants allowing the total or partial replacement of chemicals used for fertilization or protection of crops

Genetic Diversity of Rhizobia in Ethiopian Soils: Their Potential to Enhance Biological Nitrogen Fixation (BNF) and Soil Fertility for Sustainable Agriculture

Nitrogen is one of the most limiting nutrients to plant growth. It has to be fixed in the form of NH4 through chemical (fertilizer production) and biological (bacterial) processes (BNF) in the soil. The endosymbiotic associations of root nodule bacteria (rhizobia) with leguminous plants fix 200-500kg N ha-1 yr-1. Consequently, the legumes are integrated into different agro-ecosystems for plant production and soil protection. In view of the ever-increasing demand for food and feed for the burgeoning population in the country, the search for cheaper ways of enhancing soil fertility is very important. To that end, many research activities have been undertaken for the last 20 years to realize the full potential of the legume-rhizobia symbiosis in crop production and agro forestry systems. Although the pioneer research works were focused on the agronomic relationship of resident rhizobia with food legumes, recent studies encompassed rhizobial diversity and effectiveness on different pulse crops and other woody shrub and tree legumes. Some of the polyphasic studies on the rhizobia from Southern Ethiopia revealed that Ethiopian soils harbour diverse groups of rhizobia that are very distinct (more than 80%) from the hitherto known taxa of the Family Rhizobiaceae. This suggests that the country has enormous rhizobial resources for more phylogenetic studies and for the selection of elite strains to enhance effective Rhizobium-legume symbiosis in its agro ecosystems. In this review, the challenges and prospects associated with the exploitation of BNF in the country, in general, and the potential to develop and promote broad-host range inoculants to small-scale farmers, in particular, will be discussed. Keywords: Genetic diversity; Indigenous rhizobia; Legume-Rhizobium symbiosis; Nitrogen fixation Ethiopian Journal of Biological Sciences Vol. 6 (1) 2007: pp.77-9