Alien Introgression in Wheat Cytogenetics, Molecular Biology, and Genomics

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The Mediterranean group, distributed in the Mediterranean-Central Asiatic region,
consists mainly of annual species that have solitary spikelet at each rachis node (except
in the Mediterranean species of Hordeum that have three spikelet at each rachis node,
and species of Crithopsis and Taeniatherum that have two spikelets at each rachis
node). Muramatsu ( 2009 ) suggested that six genes located on homoeologous group 2
chromosomes of common wheat determine solitary spikelet per rachis node and the
2–3 spikelets per rachis node is a recessive trait. Two small genera, Dasypyrum and
Secale , have both perennial and annual species. Another characteristic of this group is
that each genus is morphologically distinct. Aegilops is the largest genus (24 species)
and Taeniatherum, Crithopsis, Heteranthelium, and Amblyopyrum are monotypic.
Natural inter-generic hybridization usually more restricted in this group in contrast to
that in the Arctic-Temperate group, perhaps due to a larger genomic diversifi cation that
creates strong inter-generic barriers. Allopolyploidy is more prevalent in this group.
The evolutionary trends in the tribe are in spike structure (erect or nodding,
spikelets per node, rachis fragile or tough, pedicels absent or present, rachilla fragile
or tough, glume tip unawned or awned, glume back rounded or keeled, caryopsis
free or adherent to lemma), longevity (perennialism or annualism), pollination
mode (cross or self), polyploidy (autopolyploidy or allopolyploidy ), geographical
distribution (Temperate-Arctic or Mediterranean), habitat (open and dry or close
and humid), and specialization of genetic systems.

Table 2.2 Classifi cation of the g enera of the Triticeae according to their distribution group and
growth habit (after Sakamoto 1991 )

Distribution group

Growth habit Rachis

Perennial Perennial + annual Annual node with:

Arctic-temperate

group (Primitive

group)

Elymus Spikelets

in groups

Hystrix

Sitanion

Leymus

Psathyrostachys

Hordelymus Hordeum

Taeniatherum

Mediterranean-

Central Asiatic

group (Advanced

group)

Crithopsis

Elymus

Agropyron Dasypyrum Heteranthelium Solitary

spikelets

Secale Eremopyrum

Triticum

Amblyopyrum

Aegilops

Henrardia

M. Feldman and A.A. Levy