33Eig ( 1929a ) defi ned traits that he considered primitive (ancestral) or advanced in
this group (Table 2.6 ). Accordingly, one may consider A. muticum, Ae. speltoides ,
T. monococcum and T. urartu, that exhibit ancestral traits, as the basal species of the
group, and Ae. umbellulata and Ae. uniaristata as the most advanced and therefore,
the youngest species. A. muticum has morphological traits, e.g., cylindrical awnless
spikelets, that differentiate it from the other diploid species of the group (Eig 1929b ).
The studies on the karyotypes of the species (Senyaninova-Korchagina 1932 ;
Chennaveeraiah 1960 ) separated the diploids into two categories: those diploids
having only metacentric or submetacentric chromosomes (the T-, A-, S-, and D-
genome species) and those with subtelocentric chromosomes (the C-, M-, N-, and
U- genome species). Stebbins ( 1950 ) considered asymmetry of centromere position
more advanced than approximate isobrachial condition since it was found in those
diploids with increased specialization of the lemmas, the rachis (with respect to
fragility) and awn development.
Dvorak and Zhang ( 1992 ), analyzing repeated DNA sequences, concluded that
A. muticum is close to Ae. caudata , Ae. comosa , Ae. uniaristata and Ae. umbellu-
lata. Terachi et al. ( 1984 ), Murai et al. ( 1989 ) and Yamane and Kawahara ( 2005 )
suggested that A. muticum is close to Ae. umbellulata while Terachi and Tsunewaki
( 1992 ) suggested that it is close to Ae. tauschii. This poses a discrepancy between
molecular phylogeny and classifi cation based on morphology. Morphologically A.
muticum resembles species of Agropyron and other perennial relatives (Eig 1929b ;
Ohta 1991 ). Amblyopyrum muticum and Ae speltoides are the only allogamous spe-
cies in the group. Allogamy is a primitive character since most perennial species in
the tribe Triticeae are allogamous. Moreover, A. muticum and Ae. speltoides are the
only species that contain B-chromosomes (Mochizuki 1957 ; Simchen et al. 1971 )
and a gene that promotes pairing between homoeologs and suppresses the effect of
Table 2.6 Eig’s ( 1929a ) defi nition of primitive (ancestral) and advanced traits in the genus
Aegilops
Ancestral traits Advance traits
Tall plant Short plants
A small number of tillers A large number of tillers
Long spike Short and compact spike
Large number of fertile spikelets per spike Small number of fertile spikelets
per spike
A large number of fl orets per spikelet A small number of fl orets per
spikelet
The glumes are shorter than the fl orets The g lumes are about the same
size as the fl orets
Awns on palea Awns on the glumes
Glumes of the apical spikelets are awnless Glumes on the apical spikeletes
are with many awns
The spikes disarticulate at maturity into spikelets with the
rachis internode that belong to them (wedge type)The spike falls entire at maturity
(umbrella type)
The grain is joined together with the chaff The grain is free2 Origin and Evolution of Wheat and Related Triticeae Species