EFFECT OF MIXED-SALT SALINITY ON GROWTH AND ION RELATIONS OF A QUINOA AND A WHEAT VARIETY

ABSTRACT

Salinity is among the most widespread and prevalent problems in irrigated agriculture. Many members of the family Chenopodiaceae are classified as salt tolerant. One member of this family, which is of increasing interest, is quinoa (Chenopodium quinoa Willd.) which is able to grow on poorer soils. Salinity sensitivity studies of quinoa were conducted in the greenhouse on the cultivar, “Andean Hybrid” to determine if quinoa had useful mechanisms for salt tolerant studies. For salt treatment we used a salinity composition that would occur in a typical soil in the San Joaquin Valley of California using drainage waters for irrigation. Salinity treatments (EC_i ) ranging from 3, 7, 11, to 19?dS?m^?1 were achieved by adding MgSO₄, Na₂SO₄, NaCl, and CaCl₂ to the base nutrient solution. These salts were added incrementally over a four-day period to avoid osmotic shock to the seedlings. The base nutrient solution without added salt served as the non-saline control solution (3?dS?m^?1). Solution pH was uncontrolled and ranged from 7.7 to 8.0. For comparative purposes, we also examined Yecora Rojo, a semi-dwarf wheat, Triticum aestivum L. With respect to salinity effects on growth in quinoa, we found no significant reduction in plant height or fresh weight until the electrical conductivity exceeded 11?dS?m^?1. The growth was characteristic of a halophyte with a significant increase in leaf area at 11?dS?m^?1 as compared with 3?dS?m^?1 controls. As to wheat, plant fresh and dry weight, canopy height, and leaf area did not differ between controls (3?dS?m^?1) and plants grown at 7?dS?m^?1. Beyond this threshold, however, plant growth declined. While both quinoa and wheat exhibited increasing Na⁺ accumulation with increasing salinity levels, the percentage increase was greater in wheat. Examination of ion ratios indicated that K⁺:Na⁺ ratio decreased with increasing salinity in both species. The decrease was more dramatic in wheat. A similar observation was also made with respect to the Ca²⁺:Na⁺ ratios. However, a difference between the two species was found with respect to changes in the level of K⁺ in the plant. In quinoa, leaf K⁺ levels measured at 19?dS?m^?1 had decreased by only 7% compared with controls. Stem K⁺ levels were not significantly affected. In wheat, shoot K⁺ levels had decreased by almost 40% at 19?dS?m^?1. Correlated with these findings, we measured no change in the K⁺:Na⁺ selectivity with increasing salinity in quinoa leaves and only a small increase in stems. In wheat however, K⁺:Na⁺ selectivity at 3?dS?m^?1 was much higher than in quinoa and decreased significantly across the four salinity levels tested. A similar situation was also noted with Ca²⁺:Na⁺ selectivity. We concluded that the greater salt tolerance found in quinoa relative to wheat may be due to a variety of mechanisms.