Differences in salinity tolerance for growth and water-use efficiency in some amaranth (Amaranthus spp.) genotypes

Amaranth (Amaranthus spp.) is a promising C-4 crop for semi-arid regions because of its high nutritive value and its ability to adapt to diverse environments. Data on the tolerance of amaranth to salinity stress are lacking. The response of four amaranth genotypes (A. tricolor, Accession '83, A. hypochondriacus, and A. cruentus) to saline water was analysed for growth, gas exchange, water use, and leaf anatomical changes. The study was conducted in a greenhouse. The treatments consisted of saline water at 0, 25 50 100, and 200 mM NaCl, equivalent to electrical conductivities of 1.2, 4.1, 7.0, 12.8, and 24 dS m(-1). respectively. Increasing NaCl in the medium decreased plant height, leaf number, and leaf area. Photosynthetic rate and stomatal conductance were significantly reduced by salinity. A. tricolor and Accession '83 did not survive in the 200 mM NaCl treatment. Shoot growth was reduced and at 50 and 100 mM NaCl the reduction was greater in A. tricolor and Accession '83 than in A. hypochondriacus and A. cruentus. Water-use efficiency increased with increasing salinity and ranged from 3.9g in A. tricolor to 6.7 dry mass kg(-1) H2O in A. cruentus when plants were salinised with 100 mM NaCl. Specific leaf area (SLA) decreased with salinity and differed between genotypes. A negative relationship between SLA and water-use efficiency was observed over the four amaranth genotypes. A. tricolor and Accession '83 had thinner leaves, more stomata per unit leaf area, and larger stomatal apertures than A. hypochondriacus and A. cruentus.