Agriculture Reference
In-Depth Information
ary structure of the gluten proteins and that it
could be employed to rapidly and accurately
screen wheat lines in early generations of the
breeding process.
100 seeds, then the 95% exact binomial confi -
dence interval indicates that there is a 0.2%-7%
admixture of the incorrect cultivar in the whole
sample. For 1 in 50, nominally the same propor-
tion, the limits are 0.05%-10.7%. For 15 seeds
in 50 (30%) of the incorrect cultivar, a propor-
tion likely to provide functional changes in con-
trasting cultivars, the uncertainty at
p
= 0.05 is
from 14% to 44%. In any technique that cannot
handle mixed samples and is required to assess
individual seeds to detect admixtures, these sta-
tistical stringencies need to be addressed in
reporting of results.
The choice of the most appropriate technique
is predicated on the purpose of cultivar identifi -
cation. If for example one desires the separation
of genotypes with fully waxy starch from partial
waxy or wild-type starch, then NIRS may be
suffi cient (Delwiche et al., 2006), although simple
screening of cut kernels with iodine to quickly
identify seeds with endosperm that does not have
the blue reaction of normal (or partial waxy)
starch to iodine may be more cost-effective. If
one needs to segregate genotypes on the basis of
high-molecular-weight glutenin subunits, such
as differentiating 2 + 12 genotypes from 5 + 10
types, then simple MFCE (Uthayakumaran et
al., 2005) or PCR-based analyses (Xu et al., 2008)
may suffi ce. Additionally the potential for MFCE
to establish quantitative estimates of the presence
of individual subunits may make it a candidate
for predicting dough properties in wheat. For
more complex distinctions between many culti-
vars, MFCE may be coupled with libraries of
gliadin patterns from the cultivars expected to be
found in a growing region so that pattern match-
ing (Wrigley et al., 1992) is possible. Use of anti-
body-based tests is also possible (Skylas et al.,
2001). The area of wheat cultivar identifi cation
was recently reviewed in brief (Wrigley et al.,
2006).
Cultivar identifi cation
Cultivar identifi cation is an important part of
“passing the test” for wheat. Several circum-
stances may allow cultivar identifi cation to be of
value: (i) identity preservation of one cultivar or
a limited group of cultivars for a specifi c market-
ing purpose; (ii) as an enforcement backup for
statutory or contractual requirements for cultivar
declaration at delivery; (iii) as a method of estab-
lishing a priori knowledge of quality traits that are
primarily under genetic control. Such traits
include kernel texture (hard or soft), seed coat
color (red or white), starch properties (with or
without
Wx-1
null alleles), and dough attributes
(via gluten composition).
Other than segregation by visually distinguish-
able market classes (where these exist) there are
a number of techniques that have been applied in
attempts to rapidly and accurately identify culti-
vars in the marketing stream where speed,
coupled with reliability, is essential. These tech-
niques include NIRS, microfl uidic capillary elec-
trophoresis (MFCE), and cultivar-identifi cation
methods based on molecular markers. Tradi-
tional methods such as identifying gliadin poly-
morphisms via electrophoresis are generally too
slow and too complex for wide adoption as routine
screening methods. Although each method has
its virtues, limitations are evident where there are
too many cultivars to identify, or where they are
highly related, or where small admixtures of
unwanted cultivars are allegedly present in a
grain lot. In the latter case stringent adherence to
correct sampling procedures is required as well
as the application of relevant statistical proce-
dures to determine confi dence limits for percent-
ages [see Clopper and Pearson (1934) for the
exact binomial confi dence interval and Agresti
and Coull (1998) for further discussion]. For
example, where 2 seeds are found to be from an
incorrect cultivar in an individual subsample of
FUTURE PERPECTIVES
For the cereal technologist there are many excit-
ing advances on the horizon that promise better,
