Genetic control of sodium exclusion in durum wheat

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, F-1, F-2, and low- and high-selected F2:3 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 F-1 progeny mean was intermediate to the mid- and low- parent means, suggesting incomplete dominance gene action. Progeny in the F-2 generation of both populations segregated for Na+ accumulation in a 15 (low Na+):1 (high Na+) ratio (χ(2)(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 (h(R)(2) = 0.43-0.90) across populations, indicating good response to selection for low Na+ accumulation in the F-2 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.