235therefore, both the Lr57 and Yr40 transfers were assumed to be induced by
homoeologous recombination. On the contrary, the Sr53 transfer occurred sponta-
neou sly in the presence of Ph1 , which ensures that in hexaploid wheat only homolo-
gous chromosomes pair and recombine. Chromosome 5M g #1 not only escapes the
diploid pairing control of wheat but also freely recombines in proximal chromo-
some regions where crossing over is usually suppressed (Liu et al. 2011b ). We fur-
ther analyzed this phenomenon by GISH, which revealed that a very small distal
region of the short arm of chromosome 5M g #1 is replaced by 5DS (3 %) and that
this chromosome is actually a spontaneous wheat– Ae. geniculata recombinant chro-
mosome and can be described as T5DS-5M g #1S•5M g #1L (D-H Koo et al., unpub-
lished). This translocation presumably occurred during the development of the
substitution line. Chromosome 5M g #2, from a different Ae. geniculata accession, is
a complete Ae. geniculata chromosome that does not have a wheat segment attached
to the distal region of the short arm, and, as a result, does not recombi ne with wheat
chromosomes in the presence of Ph1. The presence of a very small distal wheat seg-
ment in he terozygous condition not only allows recombination in this small region
of homology, but also permits crossing over in distal and proximal homoeologous
regions where recombination is usually suppressed in the presence of Ph1 (D-H
Koo et al., unpublished).
9.15 Ae. triuncialis
Ae. triuncialis L. (2 n = 4× = 28, U t U t C t C t ) is the source of the leaf rust resistance
gene Lr58. The Lr58 transfer occurred spontaneously in the progeny of a cross
between the wheat cultivar WL711 and Ae. triuncialis accession TA10438. Mole-
cular marker analysis mapped Lr58 to a wheat– Ae. triuncialis recombinant chromo-
some, T2BS•2BL-2 t #1L, where approximately 5 % of the distal end of the long arm
was derived from the long arm of a group-2 Ae. triuncialis (2 t #1L) chromosome
(Kuraparthy et al. 2007a ). The T2BS•2BL-2 t # 1L translocation present in germ-
plasm TA5605 was designated as cryptic because the Ae. triuncialis segment in this
translocation was cytologically undetec table.
Ae. triuncialis is also the source of cereal cyst ne matode ( Heterodera avenae
Woll.) resistance gene Cre7 (Romero et al. 1998 ) and Hessian fl y ( Mayetiola
destructor Say.) resistance gene H30 (Martin-Sanchez et al. 2003 ). Both transfers
occurred spontaneously. Preliminary data suggested that the H30 gene was derived
from a group-4 U t - genome chromosome and was transferred to wheat chromosome
4D. However, further work is necessary to confi rm this.
9.16 Ae. ventricosa
Doussinault et al. ( 1983 ) transfer red a gene conferring resistance to eyespot [caused by
Pseudocercosporella herpotrichoides (Fron) Dreighton], Pch1 , from Ae. ventricosa
Tausch (2 n = 4× = 28, D v D v N v N v ) to wheat chromosome 7D (Jahier et al. 1979 , 1989 ;
9 Wheat–Aegilops Introgressions