93From among the Thinopyrum species Thinopyrum ponticum [(Podp.) Barkw and
DR Dewey (syn Agropyron elongatum )] is carrying many potentially favourable
traits for wheat improvement. A number of disease resistance genes, including
Lr19 , Lr24 and Lr29 (Knott 1968 ; Sears 1973 , 1977 ), Sr25 and Sr26 (McIntosh
et al. 1977 ; Jin et al. 2007 ), Cmc2 (Whelan et al. 1986 ) and Qfhs.pur-7EL (Shen and
Ohm 2007 ), as well as genes controlling salt tolerance (Chen et al. 2004 ), yield and
biomass (Reynolds et al. 2001 ; Monneveux et al. 2003 ), were transferred from Th.
ponticum to wheat. The dwarf line 31505-1 was obtained after backcrossing 31505
to Lumai 5 (Chen et al. 2012 ). In Russia, Tzitzin selected winter wheat cultivars
from Agropyron sp. × T. aestivum crosses, which were grown in commercial produc-
tion (Zhukovsky 1957 ). Interspecifi c crosses were used to incorporate a number of
disease resistance and storage protein genes into the common wheat germplasm in
the Odessa breeding programme (Litvinenko et al. 2001 ).
The Lr19 leaf rust resistance gene was transferred to common wheat from
Thinopyrum ponticum by Sharma and Knott ( 1966 ). Lr19 is an important gene not
only due to the rust resistance conferred by this gene, but also because of the yield
increases produced in different backgrounds when alien chromatin carrying Lr19 is
introgressed in wheat. CIMMYT scientist Ricardo Rodriguez, a pre-breeder, suc-
cessfully transferred the gene into a Bluebird 2 background in the mid 1980s. Later
the Mexican National Agricultural Research Service (INI-FAP) released a wheat
cultivar carrying Lr19 named Oasis 89, which was higher yielding than its recurrent
parent Yecora 70, even in the absence of rust. This observation led to further studies
and the development of more lines carrying Lr19 (Rajaram 2001 ). According to
Reynolds et al. ( 2001 ) Lr19 was associated with increases in yield (average 13 %),
fi nal biomass (10 %) and grain number (15 %) in all the backgrounds studied. Lr19
was also associated with the increased partitioning of biomass to spike growth at
anthesis (13 %), a higher grain number per spike, and higher values of radiation use
effi ciency (RUE) and fl ag-leaf photosynthetic rate during grain fi lling. According to
Miralles et al. ( 2007 ) the Lr19 gene promoted the partitioning of assimilates to the
reproductive organs and nitrogen partitioning to the spike, resulting in an increased
number of fertile fl orets per spike and grains per unit area, without affecting the
number of spikes per unit area or crop development.
Unfortunately , the Lr19 translocation also carries a gene(s) for yellow endosperm
pigmentation that renders the resistance useless in countries where this trait is
regarded as undesirable because of quality aspects. Several modifi cations were
made to construct a shorter form of the translocation , lacking the yellow pigment
genes ( Lr19-149 ). Marais et al. ( 2001 ) carried out a yield trial with near isogenic
lines of both the original and shortened translocations, which suggested that Lr19
may cause a small reduction in kernel size and an increase in loaf volume, effects
which are not associated with Lr19-149.
Linkage drag is a great challenge for wheat breeders carrying out alien gene
introgression. A resistance gene against eyespot, caused by Tapesia spp. (formerly
Pseudocercosporella herpotrichoides ), was introduced from Aegilops ventricosa
with a closely linked gene depressing yield performance. After a conscious selec-
tion programme this unfavourable linkage was broken, and UK breeders developed
3 Wheat Breeding: Current Status and Bottlenecks