Strong correlation of wild barley (Hordeum spontaneum) population structure with temperature and precipitation variation

In this study, we present the genetic analysis of a new collection of wild barley (Hordeum spontaneum) using 42 simple sequence repeat (SSR) markers that represent the seven chromosomes. The Barley1K (B1K) infrastructure consists of 1020 accessions collected in a hierarchical sampling mode (HSM) from 51 sites across Israel and represents the wide adaptive niche of the modern barley's ancestor. According to the genetic structure analysis, the sampled sites can be divided into seven groups, and sampled microsites located on opposing slopes or in different soil types did not show significant genetic differentiation. Although the genetic analysis indicates a simple isolation-by-distance model among the populations, examination of the genetic populations' structure with abiotic parameters in an ordination analysis revealed that the combination of elevation, mid-day temperature and rainfall explains a high proportion of the variance in the principal components analysis. Our findings demonstrate that the current populations have therefore been shaped and distinguished by non-selective forces such as migration; however, we suggest that aridity and temperature gradients played major roles as selective forces in the adaptation of wild barley in this part of the Fertile Crescent. This unique collection is a prelude for the investigation of the molecular basis underlying plant adaptation and responsiveness to harsh environments.