Abstract
Adaptation to edaphic stress may have a key role in plant species range expansion. Aegilops tauschii Coss., the common wheat’s D-genome progenitor native to the Transcaucasus-Middle East region, is a good model to study the relationships between soil salinity and plant distributions: one of its intraspecific sublineages, TauL1b, drove the long-distance eastward expansion of this species range reaching semi-arid-central Asia. Salt tolerance during germination and seedling growth was evaluated in 206 Ae. tauschii accessions by treating seeds with NaCl solutions differing in concentrations. Differences in natural variation patterns were analyzed between sublineages and associated with natural edaphic condition variables, and then compared with reproductive trait variation patterns. The natural variations observed in NaCl-induced-stress tolerance had clear geographic and genetic structure. Seedling growth significantly increased in the TauL1b accessions that were collected from salt-affected soil habitats, whereas germinability did not. Principal component analysis suggested that the NaCl-induced-stress tolerances and reproductive traits might have had a similar degree of influence on Ae. tauschii’s eastward range expansion. Adaptation to salt-affected soils through increased seedling growth was an important factor for the species’ successful colonization of the semi-arid central Asian habitats. TauL1b accessions might provide useful genetic resources for salt-tolerant wheat breeds.
Highlights
Species ranges expand through individuals’ dispersal to novel habitats and/or adaptation to local environmental conditions
Adaptive phenotypic changes in the new habitats can occur rapidly within tens of generations, when the species’ standing genetic variation can provide alleles that would be favored under the new environmental conditions[4,5]
A population genetic analysis showed that the TauL1b accessions were composed of two large and one small genepools and that they could be classified into three genetic groups: (1) the accessions having alleles mostly (>50%) derived from one of the large gene pools (LowQ2); (2) the accessions having alleles mostly (>50%) derived from the other large gene pool (HighQ2); (3) the accessions having alleles almost exclusively derived from the small gene pool (Q3) (Supplementary Fig. S1)
Summary
Species ranges expand through individuals’ dispersal to novel habitats and/or adaptation to local environmental conditions. Plants’ germination, vegetative growth, root and aboveground architecture, metabolism, and reproduction may be strongly influenced by soil’s shallowness and poor drainage (physical conditions), as well as water and nutrient deficiency, acidity, alkalinity, salinity, and metal toxicity (chemical conditions) For this reason, edaphic factors might potentially explain the patterns of local adaptation. Ae. tauschii weedy-stands often occur in wheat and barley fields within the species range[13], but the species natural habitats encompass sandy seashores, deserts margins, stony hills, steppes, wastelands, roadsides, and humid temperate forests. It is a polymorphic self-pollinating diploid species with a wide geographic range in central Eurasia. This study aimed to: (1) provide a broad picture of the natural variation patterns in Ae. tauschii’s NaCl-induced-stress tolerance during its germination and early seedling growth, (2) clarify if the species’ eastward range expansion is associated with an adaptive phenotypic change in salt tolerance by comparing the natural variation patterns of lineages and sublineages in various edaphic conditions, and (3) provide insights on the importance of salt tolerance during germination and seedling growth for Ae. tauschii’s eastward range expansion
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