192
8.1.1 Construction of Genetic Maps
Whereas the levels of polymorphism between cultivars of Triticum aestivum for
RFLP mapping are very low, it is very high in T. monococcum (85 %). On eRFLP
map was constructed in T. monococcum having 335 markers (Dubcovsky et al.
1996 ). It was found that the linkage maps of barley and T. monococcum are very
highly conserved. Of the 328 mapped loci in the latter (detected with DNA probes),
18 % were duplicated, 5.9 % were triplicated, 4.6 % were quadruplicated, and 1.55
were present fi ve times. Another genetic linkage map was constructed on a set of
93R1L lines obtained from the cross of T. boeoticum × T. monococcum (Singh et al.
2007b ). The levels of polymorphism between parents were 73 % for SSR markers
and 50 % of the RFLP markers. A total of 188 polymorphic loci were mapped.
About 58 loci showed distorted segregation with most of these mapping to chromo-
some 2A m. Chromosome 1A m of the two parents showed a small pericentric inver-
sion relative to the A genome of hexaploid wheat.
8.1.2 Disease Resistance
8.1.2.1 Stem Rust Resistance
A list of current Sr genes introgressed from T. monococcum is shown in Table 8.1.
As for deployment of introgressed genes; Sr21 has not been deployed yet, but has
the potential for limited use especially in pyramids. Sr22 (RL5244) has received
limited use thus far. Sr35 has not been deployed yet, but is being stacked into pyra-
mids. Sr35 is effective against the three TTKS variants plus TRTTF a virulent race
from Yemen. Sr35 has been mapped to chromosome 3AL in T. monococcum and maps
to the distal portion of chromosome 3BL in the hexaploid map (Zhang et al. 2010 ).
T. monococcum appears to be a valuable reservoir for additional unique Sr genes. It
Table 8.1 Sources of stem rust resistance genes in Triticum monococcum
Gene SourceChromosome
location Reference
Sr21 T. monococcum 2A The ( 1973 )
Gerechter-Amitai et al.
( 1971 )
Kerber and Dyck ( 1973 )
Sr22 T. monococcum 7A Kerber and Dyck ( 1973 )
Sr35 T. monococcum 3AL McIntosh et al. ( 1984 )
1062 accessions screened (78 %
resistant to TTKSK)Rouse and Jin ( 2011a )2 new genes resistant to TTKSK Rouse and Jin ( 2011b )
102 accessions screened with 2 races Vallega ( 1979 )G. Fedak