Agriculture Reference
In-Depth Information
Table 14.1
Wheat quality traits typi-
cally evaluated as part of the Canada
Western Red Spring variety registra-
tion testing.
Wheat Quality Trait
Method
Grain protein content
Near-infared refl ectance
Flour protein content
Modifi ed Dumas, AACC Method 46-30
Milling yield
Buhler, AACC Method 26-21
Hagberg falling number
Perten, AACC method 56-81
Flour ash content
Combustion, AACC Method 08-01
Flour color
Agtron, AACC Method 14-30
Grain hardness
Rotap, AACC Method 55-30
Absorption and dough mixing
Farinograph, AACC Method 54-21
Baking test
Can. short process (Preston et al., 1982)
a
Approved methods of the American Association of Cereal Chemists (AACC
2000).
for favored alleles in specifi c
chromosome
deployment of genes that give horizontal resis-
tance (i.e.,
Lr34
). Gene pyramids are desirable
because defeated resistance genes can be com-
bined with effective genes to build new resistance
combinations that, in some instances, can be
exceedingly diffi cult for pathogens to circumvent.
For example, the leaf rust resistance in the Cana-
dian spring wheat cultivar Pasqua is believed to
contain fi ve leaf rust resistance genes (Dyck 1993).
No report exists of the Pasqua leaf rust resistance
combination being overcome by a virulent race
of
Puccinia triticina
Eriks. (B. McCallum, pers.
comm.). This scenario provides another applica-
tion of QTL analysis and molecular breeding.
First, QTL analysis can assist in identifying the
genomic location of multigenic disease resistance
traits, and this can be followed by molecular
breeding strategies (Somers et al., 2005) to
pyramid multiple genes effective against a
common pathogen, such as
Lr34
intervals.
COMPLEX TRAITS AND GENE
PYRAMIDING
Many of the traits with which wheat breeders are
concerned are complex multigenic traits, such as
grain yield, maturity, and resistance to Fusarium
head blight (FHB, caused by
Fusarium gra-
minearum
Schwabe). Environmental effects are
often important in these traits, and both additive
gene action and pleiotropic effects can be impor-
tant. Wheat breeders are continually attempting
to increase grain yield, which can often be accom-
plished through the use of new germplasm
sources. However, quality traits, which are also
usually controlled by multiple genes, are often
static or change rather slowly. The need for novel
germplasm to create new genetic combinations
that would increase grain yield is generally at odds
with the need to retain gene complexes selected
over several generations for desirable end-use
quality.
In the case of disease resistance, wheat breeders
and geneticists have worked for decades to develop
cultivars with improved disease resistance through
the introduction of novel resistance genes from
other germplasm, including wild relatives (i.e.,
Lr19
). Further, durable resistance has been gen-
erated by combining several resistance genes into
a single genotype (gene pyramid) and by the
+
Lr19
+
Lr21
.
GENETIC MAPPING
In order to perform QTL analysis and marker-
assisted selection (MAS) for wheat improvement,
we must fi rst consider genotyping and the devel-
opment of genetic maps. Over the past 20 years,
several types of DNA markers have been devel-
oped, which were often relevant to certain genetic
applications, crop species, and research budgets.
Briefl y, the primary marker types include random
amplifi ed polymorphic DNA (RAPD), restriction
