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by different farmers. These efforts resulted in numerous landraces that had a better
adaptation to a wider range of climatic and edaphic conditions and to diverse farm-
ing regimes. But, modern plant breeding practices have eroded the genetic basis of
domesticated wheat, particularly due to the replacement in many countries of the
numerous traditional varieties (landraces) by a small number of high-yielding ones
(mega varieties). The relatively narrow genetic basis of domesticated wheat reduces
their adaptability to abiotic stresses, increases their susceptibility to biotic pressures,
and limits very much the ability to improve their performance. This boosted further
the interest of wheat geneticists and breeders in the wild relatives of wheat in an
attempt to exploit their broad gene pool for the improvement of domesticated wheat.
All the species of the wheat group and many of the two subtribes of the Triticeae,
the Triticineae and the Hordeineae, can be crossed with domesticated hexaploid and
tetraploid wheat and economically important genes can be transferred to the domes-
ticated background. To make most effective the introduction of desirable alien vari-
ation into domesticated forms it is necessary to understand the cytogenetic,
molecular, genomic, and evolutionary relationships among the wild relatives as well
as between them and the domesticated wheats.
2.2 The Triticeae
The wheat group (the genera Amblyopyrum , Aegilops , and Triticum ) is classifi ed in
the tribe Triticeae Dumort of the grass family Poaceae (Gramineae). The tribe is
relatively young; it diverged about 25 million years ago (MYA) from the other
Poaceae (Huang et al. 2002b ; Gaut 2002 ). It is economically the most important
tribe of the family, giving rise to the domesticated cereals wheat, rye , and barley ,
and to several important forage grasses. Based on traditional taxonomic sense, the
tribe includes a total of 19 genera, 18 described by Clayton and Renvoize ( 1986 ),
and one, Amblyopyrum that was separated from the genus Aegilops by Eig ( 1929b )
and van Slageren ( 1994 ). The Triticeae includes about 330 species (Clayton and
Renvoize 1986 ), growing in Temperate and Arctic zones, principally in the northern
hemisphere. About 250 species are perennials that are distributed mainly in
Temperate-Arctic regions while the annuals, including the three major Triticeae
crops, wheat, barley, and rye, are mainly distributed in the east Mediterranean and
Central Asiatic regions (Table 2.1 ).
The tribe Triticeae makes a distinct natural group, having a characteristic spike
morphology that distinguishes it from other tribes in the Poaceae. It consists of dip-
loid and polyploid species with the basic haploid chromosome number x = 7. The
ancestral Triticeae karyotype have been proposed to have derived from the n = 12
ancestral grass karyotype through four centromeric ancestral chromosome fusions
(leading to functional monocentric neochromosomes), one fi ssion and two telomeric
ancestral chromosome fusions (Luo et al. 2009 ; Salse et al. 2008 ; Murat et al. 2014 ).
The chromosomes of all the species are large. About 31 % of the species are diploids
(or rather palaeopolyploids), 1 % triploids, 45 % tetraploids, 17 % hexaploids, 5 %
octoploids, 0.2 % Decaploids, and 0.2 % dodecaploids. Elymus displays the larger
M. Feldman and A.A. Levy