Biology Reference
In-Depth Information
100 lines selected from Sumai-3 x T. durum
backcross lines about 5 lines were significantly
improved in FHB resistance, indicating that
this approach is feasible but not as simple as
originally anticipated (own unpublished results).
The phenotypic expression of FHB resistance
genes in a T. durum background seems sup-
pressed. A potential suppressor for FHB resis-
tance has been located to chromosome 2A in
wild emmer wheat (Stack et al. 2002, Garvin
et al. 2009). In search of resistance sources for
durum wheat improvement, accession of its close
relatives such as cultivated emmer ( T. dicoc-
cum )orwildemmer( T. dicoccoides ) have been
evaluated and a number of QTL-mapping stud-
ies have been performed using such material
(Buerstmayr et al. 2009). Recently, promising
sources of FHB resistance have been discovered
among Tunisian T. durum accessions (Huhn et al.
2012), and this germplasm has already entered
durum wheat breeding. Ghavami et al. (2011)
performed traditional and association mapping
of breeding populations derived from crosses
with Tunisian lines. This study revealed several
QTL, with the largest effect mapping to chromo-
some arm 5BL. Association mapping in breeding
populations had the big advantage that QTL dis-
covery and development of regionally adapted
breeding lines was done simultaneously. All in
all, improvement of FHB resistance in durum
wheat seems achievable but requires intensified
research and breeding efforts.
with marker allele types of the QTL donors and
the recipient germplasm. The number of diag-
nostic markers should be increased for QTL to
be easily adopted by breeders. Therefore, the
emphasis of future research activities should be
to detect more diagnostic markers for the most
repeatable FHB QTL reported. Fine-mapping
populations can be used both for QTL valida-
tion and finding diagnostic markers with close
linkage to the FHB QTL. Alternatively, associ-
ation mapping exploiting linkage disequilibrium
in breeding populations may yield tightly linked
markers for relevant resistance QTL. MAS was
efficient in the fixation of a limited number of
well-characterized FHB resistance QTL, as out-
lined in the previous paragraphs. In addition to
detectable QTL, FHB resistance is certainly also
modulated by an unknown number of medium-
to small-effect QTL that usually remain undis-
covered in conventional QTL mapping. High-
throughput genotyping methods, using either
dense SNP genotyping platforms or sequence-
based genotyping, became available recently,
which enable unprecedented marker density and
at competitive cost. This novel development and
the refinement of statistical tools for handling
large genotype and phenotype data open the way
to apply genome-wide selection (GS) also for
small-effect QTL.
While in hexaploid wheat, both conventional
and marker-assisted breeding for improving
FHB resistance has made significant progress, in
tetraploid durum wheat, good sources of resis-
tance are still sparse and more work is needed to
identify more resistant germplasm and to deci-
pher its FHB resistance.
Conclusions and Summary
Well-mapped and validated QTL are those
on chromosomes 3BS ( Qfhs.ndsu-3BS , Fhb1 ),
5AS ( Qfhs.ifa-5A, Fhb5 ), 4B ( Fhb4 ), and 6BS
( Fhb2 ), all deriving from Asian spring wheat
sources. In addition, a few QTL from European
winter wheat were used in MAS projects. For the
purposes of MAS, diagnostic markers are avail-
able for only Fhb1 , and highly successful MAS
for Fhb1 has repeatedly been reported. Several
more FHB QTL were used in MAS programs,
especially in cases where breeders were familiar
References
Anderson JA (2007) Marker-assisted selection for Fusarium
head blight resistance in wheat. Int J Food Microbiol
119:51-53.
Anderson JA, Stack RW, Liu S, Waldron BL, Fjeld AD,
Coyne C, Moreno-Sevilla B, Fetch JM, Song QJ, Cregan
PB, Frohberg RC (2001) DNA markers for Fusarium
head blight resistance QTLs its two wheat populations.
Theor Appl Genet 102:1164-1168.
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