Agriculture Reference
In-Depth Information
Distribution of wild tetraploid wheat: (
,
) wild emmer wheat,
Triticum
turgidum
ssp.
dicoccoides
(
T. dicoccoides
);
Fig. 1.1
(
) wild Timopheev's wheat,
T. timopheevi
ssp.
araraticum
(
T. araraticum
). (
,
) Collections were tested cytogenetically.
Adapted from Zohary and Hopf (1993) and references therein.
wild subspecies of the
T. turgidum
complex.
Because of its central place in the evolution of
cultivated wheat, wild emmer is among the best
sources for obtaining insights into wheat evolu-
tion and improvement (Xie and Nevo 2008).
Triticum dicoccoides
is a valid biological species
(Miller 1992) that has a unique ecological niche
in nature, where the seed dispersal mechanism
involves “wild type” rachis disarticulation (brittle
rachis), and spikelet morphology refl ects adap-
tive-specialized traits that ensure survival in
nature (Zohary 1969). Under the human selection
system of reaping, threshing, and sowing, the
selection and maintenance of the nonbrittle phe-
notype was highly advantageous and resulted in
accelerated domestication (Miller 1992). Wild
and domesticated forms also differ in kernel mor-
phology (Van Zeist 1976); in cultivated tetraploid
species the grain is wider, thicker, and rounder
than in
T. dicoccoides
. Unique chromosomal trans-
locations (Kawahara et al., 1993; Nishikawa et al.,
1994; Joppa et al., 1995; Kawahara and Nevo
1996) and genetic polymorphisms (Nevo et al.,
1982; Nevo and Beiles 1989; Fahima et al., 1998,
1999; Nevo 1998, 2001) also characterize
T. dicoc-
coides
. This combined evidence justifi es its tradi-
tional classifi cation as a separate species, as implied
in the name
T. turgidum
ssp.
dicoccoides
,
and it is
clearly the progenitor of
cultivated tetraploid and
hexaploid wheat.
Triticum dicoccoides
is found in Israel and Syria
(which are its centers of distribution based on
genetic diversity), Jordan, Lebanon, southeast
Turkey, northern Iraq, and western Iran (Nevo
and Beiles 1989; Nevo 1998). It was discovered in
1906, in eastern Galilee on the slopes of Mt.
Hermon by Aaronsohn, who recognized its poten-
tial importance for all wheat improvement
