Biology Reference
In-Depth Information
applications for important biotic stresses in
legumes, namely soybean, peanut, common
bean, cowpea, and chickpea. Two additional
chapters deal with GAB for enhancing the tol-
erance of potato and tomato to late blight, one
of the most devastating diseases of these two
important vegetable crops. The three final chap-
ters highlight GAB efforts toward improving dis-
ease resistance in lettuce, cassava, and
Brassica
species.
linkage and linkage-disequilibrium approaches,
are becoming increasingly popular (Yu et al.
2008). The chapter reports on the use of the NAM
approach to identify genomic regions responsi-
ble for three important diseases in maize, namely
southern leaf blight, northern leaf blight, and
gray leaf spot (Benson et al. 2011; Kump et al.
2011; Poland et al. 2011). In addition, the authors
outline the potential of genomic selection to
accelerate the breeding efforts for disease resis-
tance, especially in cases where small-effect and
environment-sensitive QTLs are involved, as in
Aspergillus
ear rot and aflatoxin accumulation
(Warburton et al. 2009). These genetic studies
provide an insight into the disease resistance
mechanism, thereby helping molecular breeders
understand the genes to be used for their deploy-
ment in elite cultivars.
In the case of wheat, among several other dis-
eases, Fusarium head blight (FHB) is an age-old
and severe one (Leonard and Bushnell 2003).
Importantly, contamination caused by fusarium
secondary metabolites, known as mycotoxins,
poses a major threat to animal and human health
(Van Egmond 2004). Extensive QTL studies for
FHB resistance have led to the identification
of 19 meta-QTLs spread across wheat chro-
mosomes (Buerstmayr et al. 2009; Liu et al.
2009; Loffler et al. 2009). These GAB efforts
for FHB have been summarized in Chapter 4
by Hermann Buerstmayr, Maria Buerstmayr, and
Schweiger and Steiner. A closely linked codom-
inant marker is always a prerequisite for mak-
ing any MABC program a success. In particular,
Umn10
, a PCR-based marker linked to a major
gene (
Fhb1
) located on the long arm of chromo-
some 3B and explaining 40-50% of phenotypic
variance (Rosyara et al. 2009), is being used rou-
tinely in breeding programs of both hexaploid
and tetraploid wheat.
In barley, improving virus resistance is one of
the top research priorities because it has a serious
impact on its production, particularly in Western
Europe. Much work has been done in the recent
past toward identification of resistance genes for
four major viruses affecting barley (Ordon et al.
Improving Disease Resistance
in Cereals
Bacterial blight (BB), effected by
Xanthomonas
oryzae
pv. o
ryzae
(
Xoo
), is a major constraint for
rice production, with reported yield losses of up
to 50% (Ou 1985). Recently several genes and
QTLs have been identified for various virulent
strains. Chapter 2 by Kou and Wang provides a
comprehensive review of and valuable insights to
understanding the interaction between rice and
Xoo
pathogen. This review provides strategies
and prior knowledge for effective deployment of
resistance genes in target environment against
Xoo
pathogen. Until now, more than 35 BB rice
resistance genes have been identified and 7 of
these have been isolated. MABC has been quite
successful in the case of BB, and various genes
such as
Xa4
,
xa5
,
Xa7
,
xa13
,
Xa21
,
Xa23
in sin-
gle or in pyramided form have been introgressed
in popular varieties/parental lines such as, Samba
Mahsuri, Pusa Basmati 1, Minghui 63, and have
been developed and released in India and China
(Gopalakrishnan et al. 2008; Sundaram et al.
2008; Perumalsamy et al. 2010; Huang et al.
2012; Singh et al. 2012).
Chapter 3 by Jamann, Nelson, and Balint-
Kurti provides a comprehensive survey of the
genetic basis of disease resistance in maize,
especially against fungal diseases. In the past,
bi-parental linkage mapping was commonly
adopted for mapping important genes and QTLs.
However, in recent years, modern mapping
approaches such as nested association mapping
(NAM), which is an effective combination of
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