Abstract
Despite the agronomical and environmental advantages of the cultivation of legumes, their production is limited by various environmental constraints such as water or nutrient limitation, frost or heat stress and soil salinity, which may be the result of pedoclimatic conditions, intensive use of agricultural lands, decline in soil fertility and environmental degradation. The development of more sustainable agroecosystems that are resilient to environmental constraints will therefore require better understanding of the key mechanisms underlying plant tolerance to abiotic constraints. This review provides highlights of legume tolerance to abiotic constraints with a focus on soil nutrient deficiencies, drought, and salinity. More specifically, recent advances in the physiological and molecular levels of the adaptation of grain and forage legumes to abiotic constraints are discussed. Such adaptation involves complex multigene controlled-traits which also involve multiple sub-traits that are likely regulated under the control of a number of candidate genes. This multi-genetic control of tolerance traits might also be multifunctional, with extended action in response to a number of abiotic constraints. Thus, concrete efforts are required to breed for multifunctional candidate genes in order to boost plant stability under various abiotic constraints.
Highlights
The many ecosystem services that grain and forage legumes provide are often compromised by their sensitivity to stressful conditions causing low yield stability.at least 50% of the production of major crops, including legume, is estimated to be lost due to increased frequency of abiotic constraints such as heat, cold, drought, salinity, and low soil fertility [1]
Advanced knowledge at the morphological, physiological and molecular level has enabled breeding for candidate genes and genetic engineering for legume crops that are better adapted to stressful conditions
The extent of the stress tolerance in plants largely depends on factors that vary among genotypes and environmental conditions, as well as the complexity and severity of the imposed stress
Summary
The many ecosystem services (biologically fixed nitrogen, soil fertility improvement, health-promoting sources of protein, N-rich green-manure; diversified agriculture etc.) that grain and forage legumes provide are often compromised by their sensitivity to stressful conditions causing low yield stability. In addition to increased soil salinity, low nutrient (notably phosphorus, P) and water availability are among the most important abiotic constraints affecting legume productivity, especially in arid and semi-arid regions [2,3,4,5,6] Under these stressful conditions, the occurrence and interactions of molecular and physiological changes at different levels (transcriptomic, metabolomic, cellular, and biochemical) make plant responses highly complex, and even more so as when plants experience both abiotic and biotic constraints. A better understanding of these processes will be valuable input for strategies to improve the symbiotic nitrogen fixation (SNF) and enhance sustainable cropping systems Given their importance for promoting sustainable agriculture, legumes’ sensitivity and adaptive responses to environmental constraints need to be more deeply explored. Recent knowledge on grain and forage legumes will be explored focusing on the below-ground (roots, nodules, rhizosphere) soil–root interface in order to understand the mechanisms involved in mitigating factors such as drought, salinity and nutrient deficiency (with emphasis on P deficiency)
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