223Monneveux et al. 2000 ; Schneider et al. 2008 ; Stoyanov 2014 ). The close relationship
of Aegilops t o Triticum species makes it feasible to transfer the desirable genes from
the alien genomes of Aegilops species into wheat genomes. The earliest reported
successful artifi cial hybridization between wheat and an Aegilops species is that of
DA Godron (1863, cited in Roberts 1929 ), although a report on spontaneous inter-
generic hybrids between wheat and Aegilops neglecta Req. ex Bertol. and Ae. triun-
cialis (L.) Á. Löve was published several years earlier (Godron 1854, cited in
Andersson and de Vicente 2010 ). The vast majority of Aegilops introgressi ons into
wheat have taken place during the past century and mostly involved intentional
transfer of genes for resistance to disease s and pests (Friebe et al. 1996 ; Schneider
et al. 2008 ).
9.3 Hybrid Production
The fi rst step in the transfer of a potentially useful gene from a wild Aegilops species
to wheat is the production of an F 1 hybrid that combines the parental genomes.
Diffi culties are often encountered in this transfer process due to (a) inability to hybrid-
ize, (b) lethality of the hybrid, (c) inability of chromosomes from the two species to
pair and exchange chromosome segments, (d) instability of the incorporated alien
chromosome resulting in their elimination over generations, and (e) the resulting
resistant line being unacceptable for agriculture. McIntosh et al. ( 2013 ) stated that the
high crossability of some wh eat genotypes, particularly of Chinese origin (e.g.,
Chinese Spring), with Aegilops was determined by additive recessive kr genes. When
two species cannot be hybridized directly, a thir d species that is cross- compatible
with one has often been used as a bridging species for gene transfer. For instance,
several of the diploid relatives of common wheat cannot be hybridized easily with the
hexaploid species but can be readily crossed with tetraploid durum wheat ( T. turgidum
ssp. durum ). The derived amphiploid can then be crossed with common wheat.
Examples where resistance genes derived from Aegilops have been transferred to
common wheat via durum wheat incl ude genes transferred from Ae. ventricosa
Tausch (Doussinault et al. 1983 ; Garcia-Olmedo et al. 1984 ; Delibes et al. 1987 ).
If cross-pollination between wheat and Aegilops species results in a hybrid,
in vitro embryo culture may be required to rescue F 1 plantlets. The F 1 hybrids are
sterile and at approximately 4 weeks of age, the seedlings are treated for 18 h in an
aerated solution of 0.03 % colchicine to double the chromosome number of dividing
cells, which may result in the later production of amphidiploid tillers. Selfed seeds
on these late-developing amphidiploid tillers or BC 1 progeny (using wheat pollen)
may ensure the continuity of the hybrids. These hybrids/amphidiploids have no
value to agriculture but after further backcros sing with wheat may result in alien
chromosome addition lines carrying whole or telocentric Aegilops chromosomes.
These addition lines may be studied to confi rm that the gene(s) of interest is
expressed in a wheat background and then determine the homoeologous group of
the Aegilops chromosome carrying that character using molecular markers (Sharp
et al. 1988 ; see also review by Qi et al. 2007 ; Dundas et al. 2008 ).
9 Wheat–Aegilops Introgressions