Legumes in the reclamation of marginal soils, from cultivar and inoculant selection to transgenic approaches

Abstract

Mineral nitrogen deficiency is a frequent characteristic of arid and semi-arid soils. Biological nitrogen fixation by legumes is a sustainable and environmentalfriendly alternative to chemical fertilization. Therefore, legumes have a high potential for the reclamation of marginal soils. Such issue is becoming more urgent due to the ever-rising requirement for food and feed, and the increasing extension of salinized and degraded lands, both as a consequence of global change and irrigation practices. This manuscript reviews current research on physiological and molecular mechanisms involved in the response and tolerance to environmental stresses of the Rhizobiumlegume symbiosis. We report in particular recent advances on the isolation, characterization, and selection of tolerant rhizobial strains and legume varieties, both by traditional methods and through biotechnological approaches. The major points are the following. (1) Understanding mechanisms involved in stress tolerance is advancing fast, thus providing a solid basis for the selection and engineering of rhizobia and legumes with enhanced tolerance to environmental constraints. (2) The considerable efforts to select locally adapted legume varieties and rhizobial inocula that can fix nitrogen under conditions of drought or salinity are generating competitive crop yields in affected soils. (3) Biotechnological approaches are used to obtain improved legumes and rhizobia with enhanced tolerance to abiotic stresses, paying particular attention to the sensitive nitrogen-fixing activity. Those biotechnologies are yielding transgenic crops and inocula with unquestionable potential.In conclusion, the role of legumes in sustainable agriculture, and particularly, their use in the reclamation of marginal lands, certainly has a very promising future.

Growth and Physiological Responses ofPhaseolusSpecies to Salinity Stress

“…Due to their capacity to grow on nitrogenpoor soils, they can be efficiently used for improving saline soil fertility and help to reintroduce agriculture to these lands [46,47]. However, in legumes, salt stress imposes a significant limitation of productivity related to the adverse effects on the growth of the host plants, the root nodule bacteria, symbiotic development, and the nitrogen fixation capacity [46].…”

“…These mechanisms include (1) exclusion of Na + and Cl − from plant tissue, (2) inclusion of these ions in inert compartments or tissues, and/or (3) some means of osmotic adjustment with solutes that are compatible with the metabolic machinery of the cell [46]. Conventional plant breeding based on yield in target environments has increased production; however, physiologically based approaches utilizing molecular tools to identify key genes or provide molecular markers have the potential to take it further [47]. Accurate and selective phenotyping will enable to best use of mechanistic molecular understanding of plant responses to salinity, and mechanisms of adaptation [1].…”

Redox Regulation in Photosynthetic Organisms: Signaling, Acclimation, and Practical Implications

“…Changed ROS abundance may also be important in the regulation of the WRKY6 and WRKY 53 transcription factors that are involved in the orchestration of gene expression (52,53,417). While redox processes are important in the orchestration of senescence (287), this stage of development can in no way be viewed as a time of uncontrolled oxidation. Indeed, given the data on protein oxidation described above, the reverse appears to be correct.…”

Genomic and phenotypic analysis of Vavilov’s historic landraces reveals the impact of environment and genomic islands of agronomic traits

“…Policy and investment since the 1960’s favoured Green Revolution cereal crops, which were planted on the best agricultural land and received the lion’s share of inputs. Legumes, on the other hand, were often relegated to marginal lands where elevated temperatures, rainfed cropping systems, short growing seasons and poor soils conspire to limit yield potential 8 . Current grain legume production (e.g., chickpea, common bean, groundnut, lentil, and pigeonpea) in impoverished, food-insecure countries is often significantly short of demand.…”