Hexaploid bread wheat is generally more salt tolerant than its tetraploid progenitor. However, the physiological bases and the relative contributions of immediate effects of polyploidization and subsequently acquired adaptive changes in the salt tolerance of hexaploid wheat remained elusive. This study compared a large suite of morphophysiological traits in synthetic and natural hexaploid wheats, and their tetraploid and diploid progenitors, under normal and salt-stressed conditions, and studied subgenome-specific expression of a critical salt-tolerance gene, HKT1;5.