Deciphering salinity resistance in Amaranthus cruentus in relation to its nutritional value: a bright future for an old plant

Several amaranths (Amaranthus spp.) are neglected orphan crop. These plants with a C4-type photosynthesis are either cultivated for their leaves rich in proteins and minerals or for their seeds containing ~15% protein with a balanced amino acid content. Among them, Amaranthus cruentus is cultivated for both uses, with distinct varieties. Despite the lack of breeding effort on amaranths, they are promising crops for the current and future agro-environmental challenges. They have some good tolerance to several biotic and abiotic stresses. Soil salinity is becoming a major constraint for crop productivity worldwide, especially in arid and semi-arid areas. Four A. cruentus varieties -two for seeds production and two for leaves production, contrasted regarding their tolerance to salt)- were exposed to a NaCl (75 mM in irrigation water) in greenhouses conditions. The response of the plants was analyzed along the entire life cycle. Growth rate, photosynthesis, and transpiration rate were recorded during growth. Biomass production was also estimated. Mineral content and various metabolites (pigments, antioxidant markers) were measured, mainly in leaves. A moderate salt stress causes a moderate decrease in growth at the vegetative stage (almost no impact on leaves production), stronger at the flowering stage. Sodium mainly accumulates in the shoot. Concentration of several minerals decreases in leaves (Cu, Fe, Zn), whereas it increases for others (Na, Mg). Flavonoids content decreases, whereas chlorophyll content is stable, except in a sensitive variety. These preliminary results show that A. cruentus is a good candidate for, at least, leaves production on salt-affected areas.