The phylogeny of the polyploid wheats Triticum aestivum (bread wheat) and Triticum turgidum (macaroni wheat)

Abstract

The phylogeny of the polyploid wheats has been the subject of intense research and speculation during the past 70 years. Various experimental approaches have been employed to ascertain the diploid progenitors of these wheats. The species having donated the D genome to Triticum aestivum has been unequivocally identified as Aegilops squarrosa. On the basis of evidence from many studies, Triticum monococcum has been implicated as the source of the A genome in both Triticum turgidum and Triticum aestivum. However, numerous studies since 1968 have shown that Triticum urartu is very closely related to Triticum monococcum and that it also carries the A genome. These studies have prompted the speculation that Triticum urartu may be the donor of this chromosome set to the polyploid wheats. The donor of the B genome to Triticum turgidum and Triticum aestivum remains equivocal and controversial. Six different diploid species have been implicated as putative B genome donors: Aegilops bicornis, Aegilops longissima, Aegilops searsii, Aegilops sharonensis, Aegilops speltoides, and Triticum urartu. Until recently, evidence presented by different researchers had not permitted an unequivocal identification of the progenitor of the B genome in polyploid wheats. Recent studies, involving all diploid and polyploid wheats and putative B genome donors, lead to the conclusion that Aegilops speltoides and Triticum urartu can be excluded as B genome donors and that Aegilops searsii is the most likely source of this chromosome set. The possibility of the B genome having arisen from an AAAA autotetraploid or having a polyphyletic origin is discussed. Key words: phylogeny; Triticum aestivum; Triticum turgidum; A, B, and D genomes.