Distinct genetic regulation of flowering time and grain-filling period based on empirical study of D-genome diversity in synthetic hexaploid wheat lines

Aegilops tauschii Coss., the D-genome progenitor of hexaploid wheat, has a wide species range in central Eurasia. Large natural variation in Ac. tauschii offers potential for improving modern varieties of common wheat. Maturation time, an important agronomic trait for wheat breeding, is tied to flowering time and grain-filling period. Here, we established 82 wheat synthetic lines derived through endoreduplication, forming triploid gametes, in interspecific hybrids obtained by crossing a tetraploid wheat cultivar, Langdon, with 69 Ac. tauschii accessions. Empirical study of the hexaploid synthetics showed abundant variation in heading, flowering, and maturation time and the grain-filling period throughout the two growth seasons examined. The wide variation observed in heading time in Ac. tauschii was maintained in the hexaploid background of the synthetic wheat lines. Significantly positive correlations were observed among heading, flowering, and maturation time in the hexaploid synthetics. On the other hand, no significant correlations were found between grain-filling period and the other traits examined. Some comparisons between two selected synthetic wheat lines having similar flowering time stably exhibited differences in their grain-filling periods. These observations suggest that two major genetic pathways independently determine wheat maturation time; one controls heading and flowering time and the other regulates grain-filling period.