Legumes are well recognized for their nutritional and health benefits as well as for their impact in the sustainability of agricultural systems. The threatening scenario imposed by climate change highlights the need for concerted research approaches in order to develop crops that are able to cope with environmental stresses, while increasing yield and quality. During the last decade, some physiological components and molecular players underlying abiotic stress responses of a broad range of legume species have been elucidated. Plant physiology approaches provided general outlines of plant responses, identifying stress tolerance-related traits or elite cultivars. A thorough identification of candidate genes and quantitative trait loci (QTLs) associated with these traits followed. Model legumes like Medicago truncatula, Lotus japonicus, and more recently, Glycine max provided valuable translational approaches for dissecting legume responses to abiotic stresses. The challenge now focuses on the translation of the information gained in model systems in controlled environments to crops grown under field conditions. In this review, we provide a general overview of the recent achievements on the study of abiotic stress responses in a broad range of model, grain and forage legumes species, highlighting the different approaches used. Major accomplishments, as well as limitations or drawbacks are discussed across the different sections. Some perspectives regarding new approaches for screening, breeding or engineering legumes with desirable abiotic stress resistance traits are anticipated. These advances will support the development of legumes better adapted to environmental constraints, tackling current demands on modern agriculture and food production presently exacerbated by global climate changes.

Quality aspects of food crops have globally important market economic and health repercussions in the current climate of food security. Grain legumes have high potential for the nutritional quality improvement of foods, but limited data on manipulating seed quality is available as the primary focus has been hitherto on phenotypic and agronomic trait improvement. This has resulted in a lack of innovation and low attractiveness of legume food products that, with the emergence of novel food habits, have together contributed to reduced legume food consumption. This trend now needs to be challenged and circumvented. In this review we have assessed the key factors affecting the nutritional quality of legume seeds such as protein, starch, dietary fiber, natural antioxidant compounds and anti-nutritional factors. All have been reviewed with emphasis on how these components might influence consumer acceptance and functional properties of legume based food products. Biofortification approaches and technological processing are discussed as ways in which the nutritional value of legumes and their consumption might be enhanced. In order to increase consumption of grain legumes, we propose that efforts should concentrate on identifying nutritionally enhanced and genetically diverse germplasm, and on linking genetics with sensorial and processing quality. This will assist the development of breeding/selection tools for traits that determine consumer demand, facilitating the implementation of quality breeding objectives in legume breeding programs. Equally important, efforts should focus on developing attractive, convenient ready-to-eat and tasty legume-based food formulations, contributing to the diversification of healthier and more nutritional diets. As a result of such a targeted effort, legume cultivation and consumption could be enhanced leading to a reduction in both the global economic burden caused by malnutrition and associated chronic diseases, and the environmental impact of agriculture.

Although yield and total biomass produced by annual legumes remain major objectives for breeders, other issues such as environment-friendly, resource use efficiency including symbiotic performance, resilient production in the context of climate change, adaptation to sustainable cropping systems (reducing leaching, greenhouse gas emissions and pesticide residues), adaptation to diverse uses (seeds for feed, food, non-food, forage or green manure) and finally new ecological services such as pollinator protection, imply the need for definition of new ideotypes and development of innovative genotypes to enhance their commercialization. Taken as a whole, this means more complex and integrated objectives for breeders. Several illustrations will be given of breeding such complex traits for different annual legume species. Genetic diversity for root development and for the ability to establish efficient symbioses with rhizobia and mycorrhiza can contribute to better resource management (N, P, water). Shoot architectures and phenologies can contribute to yield and biotic constraint protection (parasitic weeds, diseases or insects) reducing pesticide use. Variable maturity periods and tolerance to biotic and abiotic stresses are key features for the introduction of annual legumes to low input cropping systems and for enlarging cultivated area. Adaptation to intercropping requires adapted genotypes. Improved health and nutritional value for humans are key objectives for developing new markets. Modifying product composition often requires the development of specific cultivars and sometimes the need to break negative genetic correlations with yield. A holistic approach in legume breeding is important for defining objectives with farmers, processors and consumers. The cultivar structures are likely to be more complex, combining genotypes, plant species and associated symbionts. New tools to build and evaluate them are important if legumes are to deliver their exciting potential in terms of agricultural productivity and sustainability as well as for feed and food.