231and #175) with recombinant chromosome Ti6AL-6S sh #1L-6AL•6AS, which carries
smaller interstitial Ae. sharonensis segments inserted into the 6AL arm.
Ae. sharonensis is also the source of the gametocidal gene Gc2 , which was
mapped to chromosome 4S sh #1 (Miller et al. 1982 ). Gc2 is available in the form
of a spontaneous wheat– Ae. sharonensis recombinant chrom osome T4BS•4BL-
4S sh #1L (TR Endo, pers. comm.). Previous attempts to produce a complete set of
wheat– Ae. sharonensis chromosome addition lines failed, and only chromosome
4S sh was recovered from eight different Ae. sharonensis accessions (B Friebe, N
Tuleen et al., unpublished). The failure to produce a complete set of chromosome
addition line s suggested that most Ae. sharonensis accessions are homozygous for
the Gc2 gene, making gene transfer from this species into wheat diffi cult. Friebe
et al. ( 2003 ) used EMS treatment to produce a knockout mutation at the Gc2 locus,
allowing the introgression of all Ae. sharonensis chromosomes (besides 4S sh ) into
wheat, and may make the gene transfer from this species more effi cient (Olivera and
Steffenson 2009 ; Millet et al. 2014 ).
9.9 Ae. searsii
Ae. searsii Feldman & Kislev ex H ammer (2 n = 2× = 14, S s S s ) is the source of stem
rust resistance gene Sr51 that was transferr ed to w heat as centric fusion or
Robertsonian translocation (Sears 1952 ; Friebe et al. 2005 ). Sr51 is located on the
short arm of the Ae. searsii chromosome 3S s #1 and is available in the form of the
Robertsonian translocations T3AL•3S s #1S, T3BL•3S s #1S, and T3DL•3S s #1S (Liu
et al. 2011a ). The level of resistance conferred by the T3AL•3S s #1S germplasm is
lower than that of ROBTs involving wheat chromosomes 3B and 3D, indicating that
the 3AS chromosome may have a modifi er that affects the expression of the Sr51
resistance.
9.10 Ae. umbellulata
Sears ( 1956 ) was the fi rst to use radiation to transfer a leaf rust resistance gene, Lr9 ,
from Ae. umbellulata Zhuk. (2 n = 2× = 14, UU) to wheat. Notably, this is the only
success case of transferring genes by irradiating pollen, all the others irradiated
seeds. Radiation treatment causes random chromosome breakage and fusion of bro-
ken ends resulting in translocation chromosomes. Although 17 different wheat– Ae.
umbellulata translocation chromosomes were produced, only one, des ignated as T4
or Transfer, showed normal male and female transmission and was used in wheat
improvement. The translocation chromosome T6BS•6BL-6U#1L in Transfer con-
s ists of w heat chromosome 6BS, most of 6BL, and a small distal segment derived
from the long arm of Ae. umbellulata chromosome 6U#1 (Friebe et al. 1995 ). Ae.
umbellulata has a highly nonsymmetrical karyotype, caused by a large number of
9 Wheat–Aegilops Introgressions