The Leguminosae (legume family) is divided into three sub-families, the Caesalpiniodeae, Mimosoideae and Papilionoideae. Here, the literature on legume-rhizobia symbioses was reviewed, and genotypically characterised rhizobia related to the taxonomy of the legumes they were isolated from. Only data from field soils were considered. The objective of the work was to assess to what extent legume specificity for rhizobial symbiont is related to legume taxonomy. Bradyrhizobium spp. were the exclusive rhizobial symbionts of species in the Caesalpinioideae but data are limited. Where tested, species within the two Mimosoideae tribes, Ingeae and Mimoseae were nodulated by different rhizobial genera. Generally, Papilionoideae species with indeterminate nodules were promiscuous in relation to rhizobial symbionts but high specificity for rhizobial partners appears to hold at tribe level for the Fabeae (Rhizobium spp.), genus level for Medicago (Ensifer spp.), Cytisus (Bradyrhizobium spp.) and Lupinus (Bradyrhizobium spp.), and species level for Galega spp. (Neorhizobium galegeae), Hedysarum coronarium (Rhizobium sullae), Cicer arietinum (Mesorhizobium spp.) and New Zealand native Sophora spp. (Mesorhizobium spp.). High legume specificity for rhizobial symbionts was linked to specific rhizobial symbiosis genes. For Papilionoideae species with determinate nodules, the Dalbergieae were primarily nodulated by Bradyrhizobium but were promiscuous with respect to Bradyrhizobium spp. while those in the Desmodieae, Phaseoleae, Psoraleae and Loteae were promiscuous across different rhizobial genera. Possible advantages and disadvantages of high specificity or promiscuity are discussed.

Type IVc Pili (T4cP), also known as Tad or Flp pili, are long thin microbial filaments, which are made-up of small-sized pilins. These appendages serve different functions in bacteria including attachment, biofilm formation, surface sensing, motility, and host colonization. Despite their relevant role in diverse microbial lifestyles, knowledge about T4cP in bacteria that establish symbiosis with legumes, collectively referred to as rhizobia, is still limited. Sinorhizobium meliloti contains two clusters of T4cP-related genes: flp-1 and flp-2, which are located on the chromosome and pSymA megaplasmid, respectively. Bundle-forming pili associated to flp-1 have been involved in competitive nodulation of alfalfa plants but the role of flp-2 remains elusive. In this work, we have performed a comprehensive bioinformatic analyses of T4cP genes in the highly competitive S. meliloti strain GR4 and investigated the role of its flp clusters in pilus biogenesis, motility and in the interaction with alfalfa. Single and double flp cluster mutants were constructed in the wild-type genetic background as well as in a flagellaless derivative strain. Our data demonstrate that both chromosomal and pSymA flp clusters are functional in pili biogenesis, and contribute to surface translocation and nodule formation efficiency of GR4. In this strain, the presence of flp-1 in the absence of flp-2 reduces competitiveness for nodule occupation.

Bambara groundnut (BG) (Vigna subterranean L. verdc) is a highly nutritious and economically important leguminous crop of African origin that forms symbiotic relationships nitrogen fixing rhizobia, but it has a low yield. Currently, there is paucity of information on effective rhizobium inoculant, (to improve the yield), for BG which are cheaper and safer alternatives to chemical fertilizers. Indigenous rhizobia strains were trapped from 54 farm soils collected at three Nigerian states (Niger, Kaduna and Kano). Six selected rhizobium strains (Bradhyrhizobium spp) were identified using 16S rDNA sequencing, applied as inoculant in field experiment using completely randomized block design and compared with USDA110 strain (Bradhyrhizobim japonicum), urea fertilizer and un-inoculated plants on 2 selected BG varieties (TVSU1248 and TVSU 631). Nutrient utilization and nitrogen fixation in plants were determined at 6 weeks while leaf chlorophyll was determined forth-nightly. Seed yield was determined at maturity. The strains increased the %nitrogen (1.33±0.10 - ≥1.37±0.05), and %phosphorous (0.48±0.02 - ≥0.51±0.02), %nitrogen fixed (21.07±2.38 - ≥61.30±6.13), nodulation (72.50±21.075 - 154.00±23.79) and leaf chlorophyll were ≥49.74±1.47mg/L, ≥51.82±1.86mg/L and ≥49.65±1.56mg/L at 2nd, 4th and 6th week after planting respectively and the yield of BG (from average of 398.6 Kgha-1 to 1454.725 Kgha-1). Seed yield was highest (1869.85±273.68 Kgha-1) in BG variety TVSU1248 using BN5 strain. Indigenous Bambara-symbiotic strains significantly increased the seed yields, and plant nutrient, showing their potential as use for inoculant to improve the yield of Bambara groundnut.

Faba bean (Vicia faba L) is the first grain legume in terms of hectarage, total production and foreign exchange earnings in Ethiopia. The current study was designed to evaluate effect of NPS and bio-organic fertilizers on the yield and yield components of faba bean in Debre Markos University research farm. A total of 16 treatments were made from the factorial combination of four levels NPS (0, 50, 100 and 150 kg ha-1) and four levels bio-organic fertilizer (Nil BOF (Bio(Nil)), rhizobium (Bio(IR)), 10 t ha-1 FYM (Bio(FYM)) and FYM+Rhizobium (Bio(FYM+IR))) in randomized complete block design (RCBD) with three replications. The Walki (EH 96049-2) variety, which is high yielding, moderate disease resistant and water-logging tolerant used as test crop. The result experiment showed that, plot treated with Bio(FYM+IR)+NPS100 treatment gave statically maximum effective number of tillers (2.73), maximum number of pods per plant (20.30), hundred seeds weight (76.11g), grain yield (5.62 t ha-1), biomass yield (10.94 t ha-1) and Harvest index (59.91%) than over other treatments received NPS fertilizer with and without bio-organic fertilizers. Therefore, the combined use of 100kg ha-1 NPS with 10 tha-1 FYM and rhizobium inoculation is superior for optimum production of faba bean in study area.

The legume-rhizobia symbiosis is one of the most important plant-microbe interactions in sustainable agriculture due to its ability to provide much needed N to cropping systems. This interaction is mediated by the mutual recognition of signaling molecules from the two partners, namely legumes and rhizobia. With legumes, these molecules are in the form of flavonoids and anthocyanins, which are responsible for the pigmentation of plants parts, such as seeds, flowers, fruits and even leaves. Seed coat pigmentation in legumes is a dominant factor influencing gene expression relating to N2 fixation, and may be responsible for the different N2-fixing abilities observed among legume genotypes under field conditions in African soils. Cowpea, Kersting’s bean and Bambara groundnut landraces with black seed coat color are reported to release higher concentrations of nod-gene-inducing flavonoids and anthocyanins when compared to the Red and Cream landraces, hence the black seed coat pigmentation is considered a biomarker for enhanced nodulation and N2 fixation. Cowpea, Bambara groundnut and Kersting’s bean with differing seed coat colors are known to attract different native soil rhizobia, confirmable by PCR-RFLP analysis of bacterial DNA from root nodules of these legumes. Even when seeds of the same legume with diverse seed coat colors were planted together in one hole, the nodulating bradyrhizobia clustered differently in the PCR-RFLP dendrograms. In one study, Kersting’s groundnut, Bambara groundnut and cowpea with differing seed coat colors were selectively nodulated by different bradyrhizobial species. Multilocus sequence analysis showed that different Bradyrhizobium species nodulated the Kersting's bean based on seed coat color. Phylogenetic analysis also placed the bradyrhizobial isolates in close proximity to different Bradyrhizobium species such as B. vignae 7-2T, B. subterraneum 58 2-1T, B. kavangense 14-3T, B. liaoningense 2281 (USDA 3622)T, B. yuanmingense LMG 21827T, B. huanghuaihaiense CCBAU 23303T, B. pachyrhizi PAC48T, and a reference type strain of B. elkanii according to seed coat color. Using 16S rDNA amplicon sequencing, we also found significant selective influences of seed coat pigmentation on microbial community structure in the rhizosphere of five Kersting’s groundnut landraces. For example, the rhizosphere of Belane Mottled landrace was dominated by Proteobacteria, while Bacteroidetes dominated the rhizospheres of the other landraces. With legumes, seed coat pigmentation therefore plays a dominant role in the selection of the bacterial symbiotic partner.

Legumes develop root nodules that harbour endosymbiotic bacteria, rhizobia. These rhizobia convert nitrogen to ammonia by biological nitrogen fixation. A thorough understanding of the biological nitrogen fixation in legumes and its regulation is key to develop sustainable agriculture. It is well known that plant hormones affect nodule formation; however, most studies are limited to model legumes due to their suitability for in vitro, plate-based assays. Specifically, it is almost impossible to measure the effects of exogenous hormones or other additives during nodule development in crop legumes such as soybean as they have huge root system in soil. To circumvent this issue, the present research develops suitable media and growth conditions for efficient nodule development under in vitro, soil free conditions in an important legume crop, soybean. Moreover, we also evaluate the effects of all major phytohormones during soybean nodulation under identical conditions. This versatile, inexpensive, scalable and simple protocol provides several advantages over previously established methods. It is extremely time-and resource-efficient, does not require special training or equipment, and produces highly reproducible results. The approach is expandable to other large legumes as well as for other exogenous additives.

Abstract: This study aimed to evaluate the application of chemical defensives and long-life inoculant, in mixtures or not, under the nodulation process of plants and the quality of soy seeds during storage. The first was carried out in a greenhouse and completely randomized design was used, in an 8 x 2 factorial scheme, with three replications, and the treatments consisted of applications of seed treatments via industrial: (T1 - control; T2 - MaximAdvanced; T3 - Fortenza; T4 - long-life inoculant; T5 - MaximAdvanced + Fortenza); T6 - MaximAdvanced + long-life inoculant; T7 - Fortenza + long-life inoculant; T8 - MaximAdvanced + Fortenza + long-life inoculant), which were sown in pots containing soils from two cultivation areas; the second in the laboratory, using a completely randomized design, in a factorial scheme 8 x 7, with four replications, with treatments consisting of eight combinations of industrial seed treatment in the greenhouse, stored for two months. That seed treatment industrial with fungicide/insecticide/inoculant, applied in isolation or not, does not influence the soy nodulation process. Soy seeds, regardless of the type of treatment received with fungicide/insecticide/long-life inoculant products, in mixtures or in isolation, may be stored for a period of 40 days for commercial purposes.

At the time of tillage, properties of the soil change, thereby changing the conditions of crop development and ultimately their productivity and quality. The effect of non-inversion tillage or no till on faba bean development is stills not widely investigated. For this reason, investigations of tillage systems from deep and shallow ploughing, chiselling, disking to no tillage were tested in Vytautas Magnus University, Agriculture Academy, Lithuania. The results showed that different tillage methods had less influence on faba bean development than meteorological conditions during the growing seasons. Soil chiselling generally showed better faba bean canopy development rates than other treatments. Faba bean roots developed somewhat better in not tilled plots. Vegetative conditions had a significant influence on faba bean development indicators. The effects of vegetative conditions during all four years of the experimentation were significantly different from each other. This shows that, due to rapid climate change, the conditions of each vegetative season become unique and require precise attention.

Abstract: Rhizobia are soil proteobacteria able to engage in a nitrogen-fixing symbiotic interaction with legumes which involves root rhizobial infection and bacterial invasion of new organs formed by the plant in response to the presence of appropriate bacterial partners. This interaction relies on a complex molecular dialogue between both symbionts. Bacterial N-acetyl-glucosamine oligomers called Nod factors are indispensable in most cases for early steps of the symbiotic interaction. In addition, different rhizobial surface polysaccharides, such as exopolysaccharides (EPS), may also be symbiotically relevant. EPS are acidic polysaccharides located out of the cell with little or no cell association that carry out important roles both in free-life and in symbiosis. EPS production is very complexly modulated and, frequently, co-regulated with that of Nod factors, but the type of co-regulation varies depending on the rhizobial strain. Many studies point out a signalling role of EPS-derived oligosaccharides in root infection and nodule invasion but, in certain symbiotic couples, EPS can be dispensable for a successful interaction. In summary, the complex regulation of the production of rhizobial EPS varies in different rhizobia and the relevance of this polysaccharide in symbiosis with legumes depends on the specific interacting couple.