Enhanced Soybean Productivity by Inoculation With Indigenous Bradyrhizobium Strains in Agroecological Conditions of Northeast Germany

Commercial inoculants are often used to inoculate field-grown soybean in Europe. However, nodulation efficiencies in these areas are often low. To enhance biological nitrogen (N) fixation and increase domestic legume production, indigenous strains that are adapted to local conditions could be used to develop more effective inoculants. The objective of this study was to assess the ability of locally isolated Bradyrhizobium strains to enhance soybean productivity in different growing conditions of Northeast Germany. Three indigenous Bradyrhizobium isolates (GMF14, GMM36, and GEM96) were tested in combination with different soybean cultivars of different maturity groups and quality characteristics in one field trial and two greenhouse studies. The results showed a highly significant strain × cultivar interactions on nodulation response. Independent of the Bradyrhizobium strain, inoculated plants in the greenhouse showed higher nodulation, which corresponded with an increased N uptake than that in field conditions. There were significantly higher nodule numbers and nodule dry weights following GMF14 and GMM36 inoculation in well-watered soil, but only minor differences under drought conditions. Inoculation of the soybean cultivar Merlin with the strain GEM96 enhanced nodulation but did not correspond to an increased grain yield under field conditions. USDA110 was consistent in improving the grain yield of soybean cultivars Sultana and Siroca. On the other hand, GMM36 inoculation to Sultana and GEM96 inoculation to Siroca resulted in similar yields. Our results demonstrate that inoculation of locally adapted soybean cultivars with the indigenous isolates improves nodulation and yield attributes. Thus, to attain optimal symbiotic performance, the strains need to be matched with specific cultivars.

Halopriming Imparts Salt Tolerance by Reducing Oxidative, Osmotic Stress and DNA Damage in Five Different Legume Varieties

Background: Salinity challenges legume production worldwide. To maintain the overall legume production, seed halopriming has been adopted as a cost-effective, farmer friendly technique, minimizing noxious effects of NaCl on plant growth. Methods: Nonprimed and haloprimed seeds were grown under different NaCl concentrations and harvested after 21 days. NaCl-induced alterations on physio-biochemical attributes and DNA damage were studied. Result: NaCl exposure in nonprimed seedlings exhibited growth inhibition, depletion in water contents, increased accumulation of H2O2, MDA and proline causing DNA damage. Conversely, in primed seedlings, these toxic effects were altered and extent of DNA damage reduced. Decreased catalase activity in nonprimed seedlings failed to detoxify the ROS generated under salinity inducing DNA damage whereas in NaCl-treated haloprimed seedlings, improved catalase activity helped to overcome such adversities favouring improved growth of all tested legume varieties.

An integrative, multidisciplinary approach to the study of the impact of climate change on legume agro-physiology and metabolism

The leguminosae are second to cereal crops in agricultural importance based on area and total production, covering 14% of the cultivated land. Within the current and near future context, legume production is threatened by various abiotic stresses associated with climate change, which are expected to increase in number and severity during the following decades. Due to the important challenge to food security, it is important to understand how future legume crops can be bred to withstand adverse environmental conditions. The overall aim of this thesis is to gain further insights on the mechanisms involved in legume response to environmental conditions ([CO2], drought and temperature) through the integrated investigation of biomass, physiological and biochemical processes and the levels of metabolites and other compounds of the plants.

Nutrient Deficiencies Are Key Constraints to Grain Legume Productivity on “Non-responsive” Soils in Sub-Saharan Africa

Leguminous plants are known to require phosphorus fertilizers and inoculation with nitrogen fixing rhizobia for optimum yield but other nutrients may also be lacking. In this study, the most limiting nutrients for legume growth were determined in soils where the crops had not responded to P and rhizobial inoculation in field trials, using the double pot technique. Soils were collected from 17 farmers' fields in West Kenya, Northern Nigeria, Eastern and Southern Rwanda, South-west and North-west Sierra Leone. Plant growth and mean biomass were measured on soils to which a full nutrient solution, containing phosphorus (P), potassium (K), magnesium (Mg), sulfur (S) and micronutrients (MN) were added, and which were compared to a control (no nutrient added), and individual omissions of each nutrient. The relationship between soil properties and nutrient deficiencies was explored. Nutrient limitations were found to differ between soils, both within and across countries. Generally, each soil was potentially deficient in at least one nutrient, with K, P, Mg, MN and S emerging as most limiting in 88, 65, 59, 18, and 12% of tested soils, respectively. While K was the most limiting nutrient in soils from Kenya and Rwanda, P was most limiting in soils from Nigeria. P and K were equally limiting in soils from Sierra Leone. Mg was found limiting in two soils from Kenya and three soils from Rwanda and one soil each in Nigeria and Sierra Leone. Micronutrients were found to be limiting in one soil from Nigeria and one soil from Rwanda. Estimates of nutrient deficiency using growth and mean biomass were found to be correlated with each other although the latter proved to be a more sensitive measure of deficiency. With few exceptions, the relation between soil parameters and nutrient deficiencies was weak and there were no significant relations between deficiency of specific nutrients and the soil content of these elements. Although our results cannot be translated directly to the field, they confirm that individual and multiple nutrient deficiencies were common in these “non-responsive” soils and may have contributed to reported low yields. This highlights the need for balanced nutrition in legume production in SSA.

Chapter 11. Legume Production

Chapter 11 of the Vegetable Production Handbook.

Legumes as a Cornerstone of the Transition Toward More Sustainable Agri-Food Systems and Diets in Europe

Legume grains are important sources of nutrients in human and animal diets and have been so for millennia. Their history as part of traditional diets dates to the origins of agriculture when their benefits for soil health and agricultural productivity started to be realized, mostly empirically, by farmers. In time, legumes have lost their popularity as human food, either because of a negative connotation as “poor man's meat,” occasional gastrointestinal side effects, or habitually longer preparation times when compared to other types of plant foods. Also, the steep rise in the consumption of meat derived foods in the last half of a century has taken a toll on replacing legumes as a major protein source. Alongside this negative trend in consumption, a negative drift in production was also observed, especially in Europe, where legumes currently occupy a minimal fraction of agricultural land. One of the main factors is a loss in competitive edge amongst farmers due to sustained lower public and private investments in breeding programs and legume adapted technology for planting, managing, harvesting, processing, and storing, when compared to cereals. Recently, increased awareness of the need to move to sustainable food systems is revitalizing legume production and consumption in Europe, leading to a compilation of policies and initiatives that aim to put legumes again as foundations for this transition. Legumes have been reinvented in a multitude of products (drinks, cereal bars, bread, meat replacers, snacks, flours, and several others) and included in farming systems of conservation agriculture, organic production, intercropping, and crop rotation, combining ancient traditions of legume production “with a spin,” incorporating new legume technological knowledge in farming systems. However, the transition has been slow and hampered by many cultural, societal, political, and economic impediments. This paper summarizes initiatives that aim to enable the comeback of legumes and their placement in a more prominent position in human diets and agricultural fields and highlights strategies that aim at overcoming the obstacles that impede achieving the development of more sustainable agri-food systems and sustainable diets in Europe.

An Annotated List of Legume-Infecting Viruses in the Light of Metagenomics

Legumes, one of the most important sources of human food and animal feed, are known to be susceptible to a plethora of plant viruses. Many of these viruses cause diseases which severely impact legume production worldwide. The causal agents of some important virus-like diseases remain unknown. In recent years, high-throughput sequencing technologies have enabled us to identify many new viruses in various crops, including legumes. This review aims to present an updated list of legume-infecting viruses. Until 2020, a total of 168 plant viruses belonging to 39 genera and 16 families, officially recognized by the International Committee on Taxonomy of Viruses (ICTV), were reported to naturally infect common bean, cowpea, chickpea, faba-bean, groundnut, lentil, peas, alfalfa, clovers, and/or annual medics. Several novel legume viruses are still pending approval by ICTV. The epidemiology of many of the legume viruses are of specific interest due to their seed-transmission and their dynamic spread by insect-vectors. In this review, major aspects of legume virus epidemiology and integrated control approaches are also summarized.

Functional and genetic diversity of native rhizobial isolates nodulating cowpea (Vigna unguiculata L. Walp.) in Mozambican soils

Identification and symbiotic characterization of indigenous rhizobial isolates are the basis for inoculant formulations needed for sustainable grain legume production. This study screened for morpho-genetic diversity of indigenous cowpea nodulating rhizobia in farmers’ fields across two contrasting agroecological zones of Northern Mozambique. The photosynthetic function induced by the isolates in their homologous cowpea was assessed. The results showed high genetic variability among the isolates based on morphology and ERIC-PCR fingerprinting. The trap cowpea genotype did not influence the diversity of isolates collected from the two different agroecologies, suggesting that the cowpea-rhizobia compatibility may be conserved at species level. Phylogenetic analysis of the 16S rRNA gene assigned representative rhizobial isolates to species in the Bradyrhizobium and Rhizobium genera, with some isolates showing high divergence from the known reference type strains. The isolates from both agroecologies highly varied in the number and biomass of nodules induced in the homologous cowpea, resulting in variable plant growth and photosynthetic activities. A total of 72% and 83% of the isolates collected from the agroecological zones 7 and 8 were respectively classified as highly effective candidates with > 80% relative effectiveness compared to plants fertilized with nitrate, indicating that elite native strains populated the studied soils. Moreover, the top 25% of high N2-fixing isolates from the two agroecologies recorded relative effectiveness ranging from 115 to 154%, values higher than the effectiveness induced by the commercial Bradyrhizobium sp. strain CB756. These strains are considered as having potential for use in inoculant formulations. However, future studies should be done to assess the ecologically adaptive traits and symbiotic performance under field conditions.

Rhizobial–Host Interactions and Symbiotic Nitrogen Fixation in Legume Crops Toward Agriculture Sustainability

Symbiotic nitrogen fixation (SNF) process makes legume crops self-sufficient in nitrogen (N) in sharp contrast to cereal crops that require an external input by N-fertilizers. Since the latter process in cereal crops results in a huge quantity of greenhouse gas emission, the legume production systems are considered efficient and important for sustainable agriculture and climate preservation. Despite benefits of SNF, and the fact that chemical N-fertilizers cause N-pollution of the ecosystems, the focus on improving SNF efficiency in legumes did not become a breeder’s priority. The size and stability of heritable effects under different environment conditions weigh significantly on any trait useful in breeding strategies. Here we review the challenges and progress made toward decoding the heritable components of SNF, which is considerably more complex than other crop allelic traits since the process involves genetic elements of both the host and the symbiotic rhizobial species. SNF-efficient rhizobial species designed based on the genetics of the host and its symbiotic partner face the test of a unique microbiome for its success and productivity. The progress made thus far in commercial legume crops with relevance to the dynamics of host–rhizobia interaction, environmental impact on rhizobial performance challenges, and what collectively determines the SNF efficiency under field conditions are also reviewed here.