Aegilops tauschii Coss. (formerly known as Aegilops squarrosa L.) is a wild diploid species that spreads in the central part of Eurasia, from the Middle East and Caucasus to southwest, central Asia, and central China. As the D genome progenitor of bread wheat, it serves as a valuable source of the “left-in-the-wild” alleles that can be used in breeding. Within its vast geographic range, Ae. tauschii populations adapt to diverse local environments and exhibit high degrees of phenotypic variability. Understanding the species’ natural trait variation patterns provides the basis for studies on the genetic mechanisms that underlie adaptation and, ultimately, is essential in enhancing the agronomic utilization of the species.

Ae. tauschii comprises two major lineages (TauL1 and TauL2) and one smaller (TauL3) lineage, which are defined by the similarity of accessions in nuclear and chloroplast molecular marker genotypes. Each lineage may correspond to an intraspecific group of accessions sharing a common ancestor that existed at some point in the past. These lineages differ in their patterns of geographic distribution: TauL1 exhibits a wide distribution across the species’ range, whereas TauL2 is restricted to the western part of the range. TauL3 has been found in Georgia.

We examined the natural variation patterns in relation to these lineages for agronomic traits, including salt tolerance during gemination and seedling growth, anther size, crossability with durum wheat, and flowering time, using a set of approximately 200 accessions (130 accessions for TauL1, 65 for TauL2, and five for TauL3) representing the entire species range. Our findings include: (1) relative to TauL1, TauL2 and TauL3 showed sensitivity to salt at the germination and seedling stages, (2) some TauL2 accessions from the southern Caspian region showed a high potential for hybridization with durum wheat in terms of anther size and crossability, and (3) some TauL1 accessions from southwest and central Asia were early flowering, whereas flowering time widely overlapped between the lineages. Overall, we conclude that the lineages provide a useful viewpoint to explore the natural variation patterns in agronomic traits in Ae. tauschii.

To facilitate the search for Ae. tauschii genes responsible for the expression of agronomic trait phenotypes, we assembled an enlarged set of non-redundant accessions (> 500 accessions). A population structure analysis showed that this set included over 350 accessions of TauL1 and approximately 150 accessions of TauL2. Additionally, the analysis revealed a small number of previously unknown TauL3 accessions from Armenia, Azerbaijan, and northern Iran.