Phenotypic effects of A(m) genomes in nascent synthetic hexaploids derived from interspecific crosses between durum and wild einkorn wheat

Allopolyploid speciation is a major evolutionary process in wheat (Triticum spp.) and the related Aegilops species. The generation of synthetic polyploids by interspecific crosses artificially reproduces the allopolyploidization of wheat and its relatives. These synthetic polyploids allow breeders to introduce agriculturally important traits into durum and common wheat cultivars. This study aimed to evaluate the genetic and phenotypic diversity in wild einkorn Triticum monococcum ssp. aegilopoides (Link) Thell., to generate a set of synthetic hexaploid lines containing the various A(m) genomes from wild einkorn, and to reveal their trait characteristics. We examined the genetic diversity of 43 wild einkorn accessions using simple sequence repeat markers covering all the chromosomes and revealed two genetically divergent lineages, L1 and L2. The genetic divergence between these lineages was linked to their phenotypic divergence and their habitats. L1 accessions were characterized by early flowering, fewer spikelets, and large spikelets compared to L2 accessions. These trait differences could have resulted from adaptation to their different habitats. We then developed 42 synthetic hexaploids containing the AABBA(m)A(m) genome through interspecific crosses between T. turgidum cv. Langdon (AABB genome) as the female parent and the wild einkorn accessions (A(m)A(m) genome) as the male parents. Two of the 42 AABBA(m)A(m) synthetic hexaploids exhibited hybrid dwarfness. The phenotypic divergence between L1 and L2 accessions of wild einkorn, especially for days to flowering and spikelet-related traits, significantly reflected phenotypic differences in the synthetic hexaploids. The differences in plant height and internodes between the lineages were more distinct in the hexaploid backgrounds. Furthermore, the AABBA(m)A(m) synthetic hexaploids had longer spikelets and grains, long awns, high plant heights, soft grains, and late flowering, which are distinct from other synthetic hexaploid wheat lines such as AABBDD. Utilization of various A(m) genomes of wild einkorn resulted in wide phenotypic diversity in the AABBA(m)A(m) synthetic hexaploids and provides promising new breeding materials for wheat.