Dual Mechanisms of Salinity Tolerance in Wheat Germplasm Lines W4909 and W4910

Soil salinity adversely affects plant growth and development, reducing the yield of most crops, including wheat. The highly salt-tolerant wheat germplasm lines W4909 and W4910 were derived from a cross between two moderately salt-tolerant lines, the Chinese Spring (CS)/Thinopyrum junceum disomic addition line AJDAj5 (AJ) and the Ph-inhibitor line (Ph-I) derived from CS/Aegilops speltoides. Molecular markers for gene introgressions in W4909 and W4910 were not reported. Four sequence-tagged site (STS) molecular markers of Ph-I were developed and tested in the above-mentioned lines and the F₂ progenies of the two crosses, Anza (AZ) × 4740 (sib of W4910) and Yecora Rojo (YR) × 4728 (sib of W4909). Additionally, homogeneity was assessed in several derivatives of W4909, 4728, W4910, and 4740 using the four markers. The four STS markers are not associated with salt tolerance, but they provide an indication of the transfer of chromatin in 3B chromosome of Ae. speltoides via Ph-I. Moreover, salt tolerance and leaf sodium concentration were determined in CS, AJ, Ph-I, 7151 (progeny of W4909), 7157 (progeny of W4910), AZ, and YR under salt treatment and control. Surprisingly, AJ had the lowest leaf sodium concentration under the control and salt treatment, indicating greater sodium exclusion than that in CS, AZ, and YR. This low level of leaf sodium concentration was heritable from 4740 to its hybrid progenies. On the other hand, the higher leaf sodium concentration, indicative of the tissue tolerance to salinity in Ph-I, had been inherited by both W4909 and W4910 and then transmitted to their hybrid progenies. One offspring line each in both W4909 and W4910 (7762 and 7159, respectively) were homozygous for the three molecular markers and lacked the marker psr1205 of Su1-Ph1 gene, making them better materials than the original lines for future research on, for example, whole-genome sequencing and gene mining. The implications of these findings for the utilization of W4909 and W4910 in breeding salt-tolerant wheat cultivars are discussed.