Unlocking salt tolerance from Fertile Crescent wild barley: evolutionary and physiological mechanisms in introgressed lines

Abstract

Soil salinity limits barley productivity, worsened by domestication bottlenecks that reduced stress-adaptive diversity. We employed a multi-origin introgression strategy using 21 wild Hordeum spontaneum accessions from diverse Fertile Crescent ecotypes to restore ancestral resilience. These foreground segments were embedded in a single cultivated background, yielding a nested backcross population (NBP) and 63 advanced recombinant lines. Parents and lines were evaluated under saline and non-saline field conditions for Na⁺/K⁺ ratio, tissue hydration, osmotic adjustment, antioxidant metabolism, and productivity. Introgression generated superior phenotypes that outperformed both parents. High-performing genotypes exhibited a coordinated tolerance strategy involving moderate Na⁺ uptake with effective tissue tolerance (likely via enhanced vacuolar sequestration), balanced osmotic adjustment to maintain hydration with minimal metabolic cost, and efficient antioxidant responses that avoided defense-yield penalties seen in wild parents. These integrated mechanisms arose from recombining adaptive alleles from multiple wild origins, with Iranian germplasm contributing strongly. A composite selection index based on these physiological traits effectively distinguished tolerant genotypes and correlated with yield stability. Our findings demonstrate that salt tolerance in barley results from balanced coordination of physiological processes rather than maximal defensive activation. Multi-origin wild introgression offers a powerful approach to restore ancestral resilience while preserving agronomic performance.