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revealed as well rearranged chromosomes, of frequent occurrence in cross- pollinated
species like L. racemosus (Qi et al. 1997 ) and L. multicaulis (Jia et al. 2002 ; Zhang
et al. 2010 ; see Sect. 11.2 ). Curiously, all the added/translocated chromosomes of
the 24 lines illustrated above appeared to belong to only one of Leymus genomes ,
namely Xm, of yet unknown origin (Wang 2011 ). Conversely, of Ns genome likely
derivation are the three L. mollis chromosomes substituted into the 2 n = 42 line
selected among F5 progenies from the cross of an octoploid Tritileymus amphiploid
( T. aestivum × L. mollis , 2 n = 56) with T. durum (Zhao et al. 2013 ). The retained L.
mollis chromosomes belong to homoeologous groups 1, 5 and 6. The triple alien
substitution line, meiotically stable and well compensated, is remarkably resistant
to stripe rust and of convenient short stature; thus, it can be employed as a bridge
parent in wheat breeding via chromosome engineering.
Desirable genes for wheat improvement have also been identifi ed in species of
the genus Agropyron (P genome, Table 11.1 ) (Han et al. 2014 and references
therein). A series of disomic addition lines was obtained from the cross of a Chinese
accession of tetraploid A. cristatum with common wheat cv. Fukuhokomugi (Wu
et al. 2006 ; Han et al. 2014 ). In all of them, SSR, EST-SSR and STS markers spe-
cifi c to the Agropyron chromosome were primarily related to homoeologous group
6; however, the group 6 markers, mainly located in the 6P pericentromeric region,
were not completely identical among the different addition lines. Moreover, there
were several markers belonging to other homoeologous groups distally located
along the various 6Ps. Such rearrangements, probably differentiating the two P
genomes of A. cristatum (see Sect. 11.2 ), led to distinguish four 6P types (6P I –6P IV )
with different genetic make-up. Among them, 6P I was proved to carry a gene(s)
conferring high grain number per spikelet and per spike and also gene(s) for resis-
tance to wheat powdery mildew (Han et al. 2014 ).
Various novel disease resistance genes have been also identifi ed on specifi c V b
chromosomes of the perennial tetraploid D. breviaristatum. Addition and substitu-
tion lines were isolated in the progeny of wheat- D. breviaristatum amphiploids
crossed with cultivated wheat, including different addition lines carrying genes for
stripe rust (Yang et al. 2008 ), as well as stem rust and powdery mildew (Liu et al.
2011 ) resistance. Marker data indicated that the V b chromosomes in the latter two
addition lines were rearranged with respect to wheat homoeologous groups. On the
other hand, various molecular markers confi rmed a group 2 homoeology for the V b
chromosome substituted into a Chinese bread wheat in place of chromosome 2D,
able to confer stripe rust resistance at the adult plant stage (Li et al. 2014 ).
Interestingly, FISH, C-banding, and PCR-based molecular marker analyses indi-
cated that the 2V b of D. breviaristatum was completely different from 2V v of D.
villosum , in line with the current view about the origin of 4 x D. breviaristatum (see
Sect. 11.2 ).
All the addition and substitution lines described above were obtained in the hexa-
ploid background of T. aestivum. Development and maintenance of intra- and inter-
specifi c aneuploid types is known to be much more diffi cult at the tetraploid level
(reviewed in Ceoloni and Jauhar 2006 ). Thus, a very limited number of chromo-
somes of alien species belonging to the secondary and tertiary gene pools (containing
C. Ceoloni et al.