Genetic control of sodium exclusion in durum wheat

Abstract

Salt tolerance in the genus Triticum is associated with low accumulation of Na⁺ in leaves. Durum and other tetraploid wheats generally have high accumulation of Na⁺ relative to bread wheat, and are salt sensitive, but a durum wheat landrace, Line 149, was found to have unusually low leaf Na⁺ accumulation. Populations were developed from crosses between 149 and the high Na⁺ accumulation variety Tamaroi, as well as between 149 and a durum wheat landrace with very high Na⁺ accumulation, Line 141. The third leaf of parental lines, F₁, F₂, and low- and high-selected F_2:3 progeny was assayed for Na⁺ uptake when grown in 150 mM NaCl. Sodium concentrations were significantly (P < 0.01) lower in the low Na⁺ uptake Line 149 compared with high Na⁺ uptake Tamaroi (5-fold greater Na⁺ accumulation) and Line 141 (7-fold greater Na⁺ accumulation). There was no evidence of any maternal genetic effect on Na⁺ accumulation. The F₁ progeny mean was intermediate to the mid- and low-parent means, suggesting incomplete dominance gene action. Progeny in the F₂ generation of both populations segregated for Na⁺ accumulation in a 15 (low Na⁺) : 1 (high Na⁺) ratio (χ²_15:1 = 0.27 and 0.46, P > 0.50n.s. for 149/Tamaroi and 149/141, respectively), indicating duplicate dominance epistasis arising from segregation of 2 interacting dominant genes. Small yet significant (P < 0.01) genotypic variation was also observed for minor genes affecting Na⁺ accumulation. Realised heritabilities were moderate to high (h²_R = 0.43–0.90) across populations, indicating good response to selection for low Na⁺ accumulation in the F₂ generation. The simple genetic control of Na⁺ accumulation suggests relative ease of selection of lines with low Na⁺ accumulation. However, presence of dominance will require selection to be delayed until after 1 or 2 generations of inbreeding, or after progeny-testing of selected low Na⁺ accumulation families.