Evidence for the origin of the B genome of bread wheat based on chloroplast DNA

Abstract

The hexaploid bread wheat Triticum aestivum L. (AABBDD) is thought to have originated through one or more rare hybridization events between Aegilops tauschii (DD) and the tetraploid Emmer wheat T. turgidum subsp. dicoccon (AABB). The progenitor of the A genome of T. aestivum has generally been accepted to be T. urartu. The origin of the B genome, however, is controversial and still relatively unknown. Research has found the B genome in T. turgidum to be closely similar to the S genome in section Sitopsis of Aegilops L.; the Sitopsis diploid species were thus proposed as the probable maternal parent in the original cross that resulted in the tetraploid T. turgidum. Moreover, the donor of the cytoplasm of T. turgidum and T. aestivum was also the donor of most, if not all, of the B genome chromosomes. The present study attempts to investigate the polymorphism of chloroplast DNA between T. aestivum and 8 different Aegilops species using cleaved amplified polymorphic sequence (CAPS) and sequencing on 28 chloroplast loci in order to identify the chloroplast donor (B genome donor) of bread wheat. A phylogenetic tree based on the data generated demonstrates that Ae. speltoides was distinct from the other Aegilops species analyzed and the most closely related to bread wheat. It can be concluded that Ae. speltoides may be the chloroplast donor to bread wheat and the donor of its B genome. Understanding hexaploid wheat origin would further its genetic improvement and is also important for the artificial development of synthetic forms.