Alien Introgression in Wheat Cytogenetics, Molecular Biology, and Genomics

200

of the accessions. It is expected that some of the resistance genes are novel. A gene
for stem rust resistance has also been introgressed into common wheat from
T. araraticum (Dyck 1992 ).

8.2.2.2 Leaf Rust Resistance

A total of 67 leaf rust resistant genes in wheat have now been defi ned (McCallum
et al. 2012 ). Of this total 35 have been introduced from alien sources including pri-
mary and secondary gene pools. Five of these genes were introgressed from T. tur-
gidum or T. dicoccoides (Table 8.4 ).
There is another example of a leaf rust resistance gene having been transferred to
bread wheat from T. dicoccoides (Marais et al. 2005 ). Suppression of the expression
of alien leaf rust resistance genes in a wheat background has always been a problem.
Some of these suppressors are being mapped (Nelson et al. 1997 ). Markers have
been assigned to three of the fi ve genes shown in Table 8.4. In general the alien Lr
genes are not widely deployed in wheat breeding programs (McCallum et al. 2012 ).

8.2.2.3 Stripe Rust Resistance

Aaronsohn ( 1910 ) who fi rst discovered T. dicoccoides predicted that it would be a
useful source of rust resistance. It was shown that many populations of wild emmer
were valuable sources of stripe resistance, and one selection in particular, G-25
was resistant to all 21 races of the fungus (Gerechter-Amitai and Stubbs 1970 ).

Table 8.4 Leaf rust resistance genes derived from emmer wheat

Lr gene

Chr.

location Origin Tester source Tester line

Gene

reference

Marker

reference

Lr14a 7BL T. turgidum Selkirk RL6013 Dyck and

Samborski

( 1968 )

Herrera-

Foessel

et al.

( 2008 )

Lr23 2BS T. turgidum Gabo RL6012 McIntosh

and Dyck

( 1975 )

Nelson

et al.

( 1997 ;

1975 )

Lr53 6BS T. dicoccoides T. dicoccoides Marais

et al. ( 2005 )

Lr61 6BS T. turgidum Guayacan Guayacan Herrera-

Foessel

et al. ( 2008 )

Herrera-

Foessel

et al.

( 2008 )

1N1A 1N1A

Lr64 6AL T. dicoccoides T. dicoccoides RL6149 JA Kolmer

et al. ( 2010 )

G. Fedak