Biology Reference
In-Depth Information
The crop is grown for a variety of purposes
such as salad, stem, and oilseed. The crop
is challenged by many biotic stresses lead-
ing to huge economic losses. In Chapter 14,
Simko reviews recent developments in MAS
for resistance to downy mildew, corky root, let-
tuce mosaic, and lettuce dieback. To achieve
these traits, both public and private sectors
are routinely utilizing allele-specific assays in
their breeding programs. Furthermore, details
and current status regarding mapping efforts
for other important traits are discussed. Impor-
tant progress has been made in generating
large-scale genomic resources/platforms in let-
tuce, such as an EST database that includes
sequences of more than 700 candidate resistance
genes (McHale et al. 2009), microarray chip
with more than 6.5 million feature Affymetrix
genechip (Stoffel et al. 2012), and complete
genome sequencing of cultivated and wild lettuce
( https://lgr.genomecenter.ucdavis.edu/; L avelle
et al. 2013), which promises to facilitate faster
diagnostics, gene expression analysis, high-
throughput genotyping, and cloning of genes.
tivars of Africa and India. The release in 2010
of cassava cultivar CR41-10 in Nigeria, made
possible through the activities of the CGIAR
Generation Challenge Program (GCP), is the
first example of MAS-derived product in cassava
(Ceballos et al. 2012). In Chapter 15, Okogbenin,
Moreno, Tomkins, Fauquet, Mkamilo, and Fre-
gene present an informative and critical review
of GAB activities in cassava.
The agricultural and horticultural uses of the
Brassica genus contribute an important part to
the human diet and to the global economy. Like
with all other crops, a plethora of pests and dis-
eases curtail the yield in Brassica . In Chapter 16,
Li and McVetty review the recent progress on the
genetics and gene mapping for disease resistance
in Brassica species. Tangible progress has been
achieved toward GAB for resistance to blackleg
and clubroot. However, the development of MAS
of sclerotinia stem rot has seen slower progress,
mostly because germplasm accessions with high
levels of resistance have yet to be identified.
Summary and Outlook
In summary, this volume presents recent
advances, useful insights, and comprehensive
reviews for GAB approaches to improve biotic
stress tolerance in a range of crops. Although
the potential for utilization of GAB in crop
improvement programs appears almost endless,
its application varies greatly among different
crop species, reflecting to a certain extent the
state-of-the-art genomics of each single species
and their economic importance. In crops such
as rice, maize, wheat, and barley, MAS and
MABC is already well integrated in breeding
programs, whereas in many others, the deploy-
ment of molecular breeding activities is under
way. Notably, GAB for several traits has recently
been initiated in orphan crops.
Thanks to the advent of NGS, it has
become possible to generate reference genome
sequence data of the main crops and also to
(re)sequence several varieties/lines. In parallel,
modern genetic mapping approaches such as
Improving Disease Resistance in
Cassava and Brassica
In addition to the aforementioned cereal, legume,
and vegetable crops, Volume I includes GAB
activities in cassava and Brassica , two other
important crops for human diet. Cassava, a
starchy root crop, is a major food source for
more than 800 million people in Sub-Saharan
Africa, Asia, and South America. It is culti-
vated on more than 20 million hectares, with an
annual production of more than 240 million tons
(FAO 2011). Cassava suffers from several biotic
stresses and is highly vulnerable to viral diseases.
Cassava mosaic disease (CMD), caused by cas-
sava mosaic Gemini virus, is one of the major
viral diseases of cassava, causing reported yield
loss of up to 40% (Taylor et al. 2004). Much suc-
cess has been achieved in identification of molec-
ular markers for CMD, and MAS for this trait is
currently being employed in several popular cul-
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