Genetic mapping of the genes for glaucous leaf and tough rachis in Aegilops tauschii, the D-genome progenitor of wheat

Glaucous leaf and tough rachis phenotypes are rare in Aegilops tauschii, the D genome donor to common wheat ( Triticum aestivum). The genes for glaucous leaf and tough rachis were mapped using microsatellite probes in A. tauschii. The glaucous phenotype was suppressed by the inhibitor W2(I) located on chromosome 2DS. The gene W2(I) was mapped to the distal part of 2DS, and was unlinked to the centromere. This suggests that the distance of the W2(I) locus from the centromere was maintained during the evolution of hexaploid wheat from its diploid progenitors as the inhibitor gene is at the same position in A. tauschii and bread wheat. The Br-t ( Brittle rachis of A. tauschii) locus was located on the short arm of chromosome 3D, and was 19.7 cM from the centromeric marker, Xgdm72.3D. Br-t causes breakage of the spike at the nodes, thus creating barrel-shaped spikelets, while Br-1 in hexaploid wheat causes breakage above the junction of the rachilla with the rachis such that a fragment of rachis is attached below each spikelet.