237Aegilops species into wheat through chromosome translocation or homoeologous
recombination, and several of the genes such as Lr9 , Pch1 , Yr17 , Lr37 , and Sr38
have been used in wheat production (Jahier et al. 1989 ; Ambrozková et al. 2002 ).
However, in most cases, these were defeated by new variants of the respective
pathogens. If such genes transferred from alien species are to be used in the future,
they sho uld be used responsibly in gene combinations that may extend the durabil-
ity and compensate for the considerable effort in their development.
Based on this review, we are aware of 41 unique resistance genes that were trans-
ferred to wheat from approximately 30 accessions representing 12 Aegilops species.
Among the transferred genes, Ae. speltoides alone accounted for the origins of 12
genes, approximately one-third of the total genes transferred. Most of the thousands
of Aegilops accessions maintained in various genetic resource centers worldwide
(Monneveux et al. 2000 ) remain untapped for wheat improvement. Until now the
genetic resources in the primary gene pool of wheat have been used in wheat breed-
ing; increased emphasis is now needed to transfer more genes for resistance to
pathogens and pests, tolerance to a biotic stresses, and increased yield potential from
Aegilops species of the secondary gene pool into wheat for future wheat breeding
programs.
Alien gene introgression has not been ef fi ciently used in developing breeding-
ready germplasm because selection of new homoeologous recombinants has been a
tedious and laborious task in the past (Niu et al. 2011 ). However, the high through-
put marker technologies that are recently available have greatly increased the
effi ciency for the precise identifi cations of desirable recombinants from large popu-
la tions (Niu et al. 2011 ; Tiwari et al. 2014 ). We anticipate that the availability of
genomic tools and rich genetic resources (i.e., wheat– Aegilops amphiploids and
chromosome addition, substitution, and translocation lines) will facilitate the future
endeavors of w heat– Aegilops introgressions for wheat improvement.
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9 Wheat–Aegilops Introgressions