32
barrel and umbrella types, and in eco-geography, occupying well-defi ned ecological
niches. All the species have distinct and well-defi ned genome s, all with 2 n = 2 x = 14
chromosomes but with different genome sizes and pairing patterns in inter-specifi c
and inter-generic hybrids (Table 2.5 ).
The diploid species are distributed in Southwest and Central Asia. The center of
the distribution is in southeast Turkey, i.e., the northern part of the fertile-crescent
belt. Six species ( A. muticum , T. monococcum subsp. aegilopoides , T. urartu , Ae.
speltoides , Ae. caudata , and Ae. umbellulata ) are distributed in the central part of
the group distribution (Table 2.5 ). Several species of the S genome group ( Ae. bicor-
nis , Ae. longissima , Ae. sharonensis and Ae. searsii ) are found south of the center,
the species of the M/N-genome group ( Ae. comosa and Ae. uniaristata ) west of the
center, and Ae. tauschii is in the eastern part of the distribution area. The geographi-
cal distribution of the various diploid species indicates that the group has undergone
an extensive differentiation in its early stages of development. Southeast Turkey is
the geographical center of the group distribution and thus, is presumably the center
of origin of the genus.
The species grow in warm countries with a short and moist winter and long, dry
hot summer. They do not grow in mountains higher than 1800 m or in the deserts.
The species are relatively restricted in their distribution and are specialized in their
ecological requirements, usually occupying well-defi ned habitats with specifi c
edaphic or climatic conditions. Some of the diploids ( Ae. speltoides , Ae. tauschii ,
Ae. umbellulata and the wild subspecies of T. monococcum ) show wider ecological
amplitudes correlated with their weedy tendency.
Natural hybridization between diploid species is a rare phenomenon. In spite of
the fact that several of the diploids have massive spatial contact, inter-specifi c
hybrids were reported between only two of these species, Ae. longissima and Ae.
sharonensis (Ankori and Zohary 1962 ). The two species are closely related, chro-
mosomal pairing in meiosis of the F 1 hybrids is complete (fi ve bivalents and one
translocation ) and fertility is high, and the only isolation between them is their dif-
ferential ecological requirements.
The genome s of the diploid species are distinct from each other. On the basis of
chromosomal pairing at meiosis of the inter-specifi c and inter-generic hybrids and
on the basis of hybrid fertility, Kihara ( 1954 ) defi ned the genomes of most diploid
species, that of Ae. searsii was formulated by Feldman et al. ( 1979 ). The genomes
of A. muticum , Ae. uniaristata , Ae. umbellulata , T. monococcum and T. urartu were
revised by Kimber and Tsunewaki ( 1988 ). Based on the genomic divergence, the
diploid species of the group are classifi ed in the following seven groups (Table 2.5 ):
- T-group ( muticum ).
- S-group ( speltoides , bicornis, longissima , sharonensis, and searsii ).
- A- group ( monococcum and urartu ).
- D-group ( tauschii ).
- C-group ( caudata ).
- M-group ( comosa and uniaristata ).
- U-group ( umbellulata ).
M. Feldman and A.A. Levy