Agriculture Reference
In-Depth Information
Chapter 14
State of QTL Detection and Marker-
Assisted Selection in Wheat Improvement
Daryl J. Somers and Gavin Humphreys
SUMMARY
(5) In the future, microarray-based gene
expression data will be a new source of
phenotypes to map gene expression pro-
fi les in relation to measurement of the
physical properties of wheat.
(6) Wheat is generally bred and improved by
selection for visual traits such as height,
lodging, and grain yield. This is labor-inten-
sive and marker-assisted selection (MAS)
can assist with selection for these traits.
(7) Wheat breeding programs can combine
MAS and doubled-haploid technology,
fi rst to screen parents with markers and
then to screen haploids prior to chromo-
some doubling, to reduce costs and increase
effi ciencies of breeding.
(8) Perfect markers, or markers within genes
controlling traits, are ideal, with no recombi-
nation expected between the trait and gene.
(9) Field performance and end-use quality
testing of wheat breeding materials will con-
tinue to be the ultimate evaluation methods
in the development of new wheat cultivars.
(1) Quantitative trait locus (QTL) analysis is
the merger of genotyping and phenotyping
data to draw associations of traits with
specifi c chromosome regions; QTL analy-
sis hinges on having a good genetic map of
the wheat population.
(2) Wheat genetic maps have improved for
over 20 years in both number and quality
of markers, beginning with restriction
fragment length polymorphism (RFLP)
and advancing to single nucleotide poly-
morphisms (SNPs).
(3)
Hundreds of QTLs have been published
for disease, agronomic, and quality traits in
wheat, including simply inherited and
complex, polygenic traits.
(4)
Association mapping is emerging as a new
approach for mapping quantitative traits.
Wheat and the associated technical
resources appear to be amenable for asso-
ciation mapping.
INTRODUCTION
global production was approximately 571 million
tonnes from 211 million hectares. Wheat supplies
humanity with 20% of its caloric intake (Western
Organization of Resource Councils 2002). Thus,
it is not surprising that wheat breeding continues
to develop the crop and that the most modern
plant breeding techniques are being applied to its
improvement.
This chapter will examine the use of quantita-
tive trait locus (QTL) analysis; QTL analysis is a
Wheat is a crop of great historical signifi cance. Its
domestication approximately 10,000 years ago
marks a turning point for humanity. The cultiva-
tion of crops including wheat allowed early humans
to move from hunter-gatherers to agriculturalists.
Wheat continues to be of great importance in our
age. It is the most widely cultivated and is third
to maize and rice in global production. In 2000,
