Mapping of the K+/Na+ discrimination locus Kna1 in wheat

In saline environments, bread wheat, Triticum aestivum L. (genomes AABBDD), accumulates less Na⁺ and more K⁺ in expanding and young leaves than durum wheat, T. turgidum L. (genomes AABB). Higher K⁺/Na⁺ ratios in leaves of bread wheat correlate with its higher salt tolerance. Chromosome 4D from bread wheat was shown in previous work to play an important role in the control of this trait and was recombined with chromosome 4B in the absence of the Ph1 locus. A population of plants disomic for 4D/4B recombined chromosomes in the genetic background of T. turgidum was developed to investigate the genetic control of K⁺/Na⁺ discrimination by chromosome 4D. Evidence was obtained that the trait is controlled by a single locus, designated Kna1, in the long arm of chromosome 4D. In the present work, K⁺/Na⁺ discrimination was determined for additional families with 4D/4B chromosomes. The concentrations of Na⁺ and K⁺/Na⁺ ratios in the youngest leaf blades clustered in two nonoverlapping classes, and all recombinant families could be unequivocally assigned to Kna1 and kna1 classes. The Kna1 locus scored this way was mapped on a short region in the 4DL arm and was completely linked to Xwg199, Xabc305, Xbcd.402, Xpsr567, and Xpsr375; it was also mapped as a quantitative trait. The results of the QTL analysis, based on the K⁺/Na⁺ ratios in the young leaves of greenhousegrown plants and flag leaves of field-grown plants, agreed with the position of Knal determined as a qualitative trait. Several aspects of gene introgression by manipulation of the Ph1 locus are discussed.