The ability of wheat to maintain a low sodium concentration ([Na +]) in leaves correlates with improved growth under saline conditions. This trait, termed Na + exclusion, contributes to the greater salt tolerance of bread wheat relative to durum wheat. To improve the salt tolerance of durum wheat, we explored natural diversity in shoot Na + exclusion within ancestral wheat germplasm. Previously, we showed that crossing of Nax2, a gene locus in the wheat relative Triticum monococcum into a commercial durum wheat (Triticum turgidum ssp. durum var. Tamaroi) reduced its leaf [Na +] (ref. 5). Here we show that a gene in the Nax2 locus, TmHKT1;5-A, encodes a Na +-selective transporter located on the plasma membrane of root cells surrounding xylem vessels, which is therefore ideally localized to withdraw Na + from the xylem and reduce transport of Na + to leaves. Field trials on saline soils demonstrate that the presence of TmHKT1;5-A significantly reduces leaf [Na +] and increases durum wheat grain yield by 25% compared to near-isogenic lines without the Nax2 locus.