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mapping, QTL validation, and the development
of improved breeding lines with high prospec-
tive for cultivar release. This approach offers
a big advantage over traditional QTL mapping,
which is often based on experimental popula-
tions, usually not suitable to deliver adapted cul-
tivars directly.
Many breeding programs use
Fhb1
success-
fully as an important resistance source. Reliance
on a narrow genetic basis bears the potential
risk of resistance breakdown. Fortunately, resis-
tance for FHB in wheat appears to be neither
race-specific nor species-specific (van Eeuwijk
et al. 1995). No breakdown of an FHB resistance
gene has been reported, and FHB resistance is
therefore considered durable at the present time
(Buerstmayr et al. 2012). The risk of pathogen
adaptation is possibly low because Fusarium
is an opportunistic, facultative pathogen that
survives well as a saprophyte, other than, for
instance, the cereal rusts and powdery mildew.
orange blossom wheat midge resistance (
Sm1
),
and leaf rust resistance (
Lr21
). In addition, the
genetic background was monitored with mark-
ers to accelerate restoration of the elite genetic
background at each backcross. This approach
resembles a breeding-by-design scheme where
one aims to pyramid desired alleles in an “opti-
mal” genotype (Peleman and van der Voort
2003). Somers et al. (2005) were successful
in establishing the desired lines within a rela-
tively short period of only 25 months, but they
did not report about a phenotypic evaluation of
the new germplasm carrying the desired alleles.
Therefore, the obtained selection gain with this
approach remains unknown.
A fairly large QTL evaluation and marker-
assisted breeding project was performed by
McCartney et al. (2007), who aimed to trans-
fer QTL from three exotic sources—Nyu-Bai,
Sumai-3, and Wuhan-1—into elite Canadian
spring wheat cultivars and measured the effects
on three traits indicative for FHB resistance
(visual scores of FHB index and severity, percent
of Fusarium-damaged kernels, and DON content
in the harvested grains) and several agronomic
and grain quality traits. They reported that the
4B FHB resistance QTL from Wuhan-1 was the
most efficient QTL improving FHB resistance,
but at the same time it was associated with an
increase in plant height. The Wuhan-1 2D, Nyu-
Bai 3BSc, Sumai-3 3BSc, Nyu-Bai 5AS, and
Sumai-3 5AS alleles were also effective FHB
resistance alleles. There was a tendency that
recombinant lines possessing two or three resis-
tance alleles had higher resistance than the lines
with single resistance alleles. The three measures
for FHB resistance—visual scores, percent of
Fusarium-damaged kernels, and DON content in
the harvested grains—were highly correlated.
Miedaner et al. (2006), generated a four-
parent recombinant population involving two
regionally adapted German spring wheat culti-
vars (Munk, Nandu) and two experimental lines
carrying either the FHB resistance QTL at 3BS
and 5A derived from CM-82036 (Buerstmayr
et al. 2002, 2003) or the QTL on 3A from
MAS for QTL Other than
Fhb1
and
MAS for Multiple QTL
Simultaneously
A repeatedly detected QTL for type 2 resis-
tance has been mapped to chromosome 6BS
and a QTL governing mainly type 1 resis-
tance at chromosome 5A, both again descending
from Asian resistance sources (Buerstmayr et al.
2009). The QTL on 6B has been fine-mapped
2 cM from
Xgwm644
by Cuthbert et al. (2007)
and designated
Fhb2
. The QTL on 5A has been
fine-mapped between
Xgwm304
and
Xgwm415
in Wangshiubai-derived populations by Xue et al.
(2011) and designated
Fhb5
. In two QTL valida-
tion populations analysed by Yang et al (2003)
in addition to
Fhb1
as described earlier, a signif-
icant effect was associated with the SSR marker
Xgwm644
at chromosome arm 6BS (most likely
Fhb2
) in one population.
Somers et al. (2005) created a multiway back-
crossing scheme for assembling complex geno-
types. This included two backcrosses and selec-
tion for a total of six FHB resistance QTL,
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