277rearrangements in the course of polyploid evolution, with presence of St/S genomic
DNA confi ned to pericentromeric regions (as in J s type chromosomes, see Chen
et al. 1998 ). In any case, hybridization to the St/S genomic DNA, whether complete
or segmental, represents a distinctive mark of the genomic origin of the Thinopyrum
chromosome(s) involved. However, the picture has been further complicated by
evidence of hybridization of J s chromosomes with either genomic DNA or a repeti-
tive sequence of the V genome of the genus Dasypyrum (see ahead), suggesting the
involvement of V genome in the evolution of the J s genome (Kishii et al. 2005 ;
Mahelka et al. 2011 ; Deng et al. 2013 ). Very recently, comprehensive reassess-
ments have been provided for some of the most controversial issues of biosystemat-
ics and evolutionary relationships of perennial Triticeae species (Wang and Lu
2014 ; Wang et al. 2015 , and references therein). One of them concerns the origin
and genome constitution of Th. intermedium , which appears to be now nearly
resolved. Presence of the St genome from Pseudoroegneria is substantiated by all
studies, hence considered unequivocal. Moreover, based on assays with EST-SSR
primer sequences derived from the putative diploid progenitor species carrying the
St, J b , and J e genomes , the St genome in Th. intermedium results the least modifi ed
from the present-day Pseudoroegneria diploids. On the other hand, the same assays
showed both J and J s to differ from present day J e ( Th. elongatum ) and J b ( Th.
bessarabicum ) genomes , respectively: the former distinction (J vs. J e ) would be
based on presence of long-terminal repeat sequences of rye (R genome) origin, the
latter (J s vs. J b ) on presence of repetitive sequences of Dasypyrum (V genome) deri-
vation. Taking into account such evidence, a novel designation has been proposed
for the Th. intermedium genome formula, that is J vs J r St, with J vs and J r representing
ancestral genomes of J b and J e (Wang et al. 2015 ).
A complex history of genome rearrangements has been also described for spe-
cies of the genus Elymus (Mahelka and Kopecky 2010 ; Zeng et al. 2013b ; Sun 2014 ;
Wang et al. 2014 ; Wang and Lu 2014 ), the largest genus in the Triticeae tribe,
including, in its broadest sense, around 200 species that are widely distributed all
over the world. Elymus is an exclusively allopolyploid genus, in which fi ve basic
genomes (St, H, Y, P, and W; Table 11.1 ) have been identifi ed (Wang 2011 ; Wang
and Lu 2014 ). Among them, the St genome is recognized as common to all Elymus
species, while Y, another pivotal genome of the genus, is still of debated origin (Sun
2014 ; Wang and Lu 2014 ).
Chromosomal rearrangements were also frequently detected in species of the
polyploid Leymus genus, such as tetraploid L. racemosus and L. multicaulis (Qi
et al. 1997 ; Jia et al. 2002 ; Zhang et al. 2010 ; see Sect. 11.3.2 ). All Leymus species
are based on the Ns-genome from Psathyrostachys (see ahead) and the Xm-genome
of still unknown origin, with genomes P of Agropyron and F of Eremopyrum triti-
ceum hypothetically considered in its ancestry (reviewed in Wang and Lu 2014 ).
However, a different genomic constitution has been recently proposed (Anamthawat-
Jónsson 2014 ). The study, based on FISH experiments with Leymus specifi c dis-
persed retroelement-like repeats as probes, showed them to be distributed over all
Leymus chromosomes, without any differentiation between chromosomes. The
same repeats were also abundant in the Ns genome progenitor in Leymus , i.e.,
11 Wheat-Perennial Triticeae Introgressions: Major Achievements and Prospects