Wheat Evolution, Domestication, and Improvement - Wheat Science and Trade - page 8

largest of the wheat genomes and, because of the
large degree of change at the DNA level, the true
donor of the B genome since polyploid formation
has been very diffi cult to establish. It would be
useful to test representatives of A- and B-genome
donors from across their geographic ranges to
settle some of the past and present controversies
over their origins. See the discussions based on
genomic in situ hybridization (GISH) molecular
cytogenetics by Belyayev et al. (2000) and Yen and
Baenziger (1996). Regardless, since the cytoplasm
donor is the female in the original cross creating
the polyploid and is always listed fi rst in any pedi-
gree, the tetraploid genome designations should
technically be BBAA or GGAA.

Caspian Sea region approximately 10,000 years
ago. Notably, T. dicoccoides wheat is more adapted
to Mediterranean environments, whereas noncul-
tivated hexaploid wheat grows in cooler and more
continental parts of Europe and western Asia
(Fig. 1.1). Thus, T. dicoccoides deserves a particu-
lar in-depth study as suggested by Aaronsohn
(1910, 1913), since it is the main genetic resource
for improving both tetraploid and hexaploid
wheat. Here we review theoretical and applied
studies on T. dicoccoides that are important for all
polyploid wheat improvement, including genetic
structure across its range and its genetic resources.
These topics are critically important to overcome
the dangerous process of homogeneity occurring
in all cultivated wheat gene pools. In addition, we
will discuss the genome organization and evolu-
tion of T. dicoccoides .
Genetic and morphological evidence clearly
indicates that the cultivated tetraploid turgidum
wheat is closely related to the wild wheat, T.
dicoccoides (Korn), which is native to the Near
East and is traditionally called wild emmer wheat
(Zohary 1969; Chapman et al., 1976; Miller 1987,
1992; Harlan 1992; Zohary and Hopf 1993;
Feldman et al., 1995). Triticum dicoccoides (Fig.
1.1) is a tetraploid containing the A (male) and B
(female) genomes and is the female progenitor of
all hexaploid wheat species. Triticum aestivum is
the most important of the hexaploid wheats, fol-
lowed by several primitive hulled types (spelta
wheat) and numerous modern free-threshing
forms (Zohary and Hopf 1993).

Emmer and durum wheat
Origin of Triticum turgidum
Triticum urartu exists only in its wild form,
contains 4.93 pg DNA (http://data.kew.org/
cvalues/introduction.html), and supplied the
male parent of tetraploid wheat (Feldman and
Sears 1981), including several cultivated species.
The most important are T. turgidum (BBAA),
containing 12.28 pg DNA (http://data.kew.org/
cvalues/introduction.html), and the sometimes
cultivated, non-free-threshing T. timopheevi ,
which contains 11.30 pg DNA (http://data.kew.
org/cvalues/introduction.html) and includes
wild subspecies T. timopheevi araraticum (Jakubz.)
Mac Key and cultivated subspecies timopheevi =
T. turgidum ssp. timopheevi (Zhuk.) . Triticum tur-
gidum is further divided into several species,
including T. turgidum ssp . dicoccoides (Korn. Ex
Asch. and Graebn.), which is well known as the
progenitor of all modern cultivated polyploid
wheat species—that includes T. turgidum ssp.
durum (Desf.) Husn., which is widely cultivated
and is commonly called durum or macaroni
wheat.
Outside the Fertile Crescent area, where T.
dicoccoides wheat (Color Plate 1) reached the range
of Ae. tauschii , the two species hybridized (Van
Zeist 1976; Van Zeist and Bakker-Heeres 1985)
and formed the hexaploid wheat group. This key
hybridization event most likely occurred in the

Origin of Triticum dicoccoides (wild emmer)
Triticum dicoccoides is an annual, is predominantly
self-pollinated, and has large and brittle ears with
large elongated grains (Nevo et al., 2002), similar
to cultivated emmer and durum wheats. It is the
only wild ancestor in the genus Triticum that is
cross-compatible and fully interfertile with culti-
vated T. turgidum wheat. Hybrids between wild
T. dicoccoides and all members of the T. turgidum
complex show normal chromosome pairing in
meiosis. Natural hybrids do occasionally form
between cultivated tetraploid wheat and T. dicoc-
coides , so T. dicoccoides is sometimes ranked as the