Agriculture Reference
In-Depth Information
As for the merits of hybrid wheat, progress
continues to be made on the hybridization process
using CMS (Chen 2003). In the US southern
Great Plains for the period from 1975 to 1995,
wheat hybrid performance was compared to con-
temporary pureline performance (Koemel et al.,
2004). The wheat hybrids had higher grain yields
than purelines, but were not more or less stable
than purelines. In one way these results are
remarkable in that throughout this period, the
investment in human and other resources would
most likely be equal or higher in pureline breed-
ing programs. Hence the hybrid advantage was
developed with less resources.
mercially, transgenic wheat will be available in the
future, because its potential and competitive
advantages manifested in other crops are too great
to preclude its adoption. New or traditional (e.g.,
organic) markets will be developed for those not
desiring transgenic foods.
As molecular marker technology continues to
decrease in cost and increase in effi ciency, marker-
based breeding methods (Bernardo and Yu 2007)
will become more prevalent. However, in order
to truly use these methods, precise and reliable
phenotypic evaluations will be needed to link with
the marker data. In this case, the best statistical
experimental and genetic designs will need to be
used, which may drive programs to doubled
haploid technologies where homozygous lines are
evaluated phenotypically, at least to determine
marker values and epistatic interactions. The
advantage of using doubled haploid lines in this
process is that elite doubled haploid lines can be
used directly for release and, as all breeding pro-
grams are a form of recurrent selection, numerous
advantages exist for doubled-haploid-based recur-
rent selection (Baenziger et al., 2001).
As markers and the underlying genes that affect
major traits are identifi ed, it may be possible
to incorporate genes into simulation models
for growth and development and productivity
(Baenziger et al., 2004). There are two important
reasons for this research. The fi rst is that, despite
the hundreds of environments that a candidate
line will be tested in before release, a breeder can
only estimate the thousands of farms (environ-
ments) where a successful cultivar may be grown.
Though it may be unrealistic for a crop model to
predict on the basis of genotype how a given cul-
tivar will perform in environments that the culti-
var has never been tested—especially for those
extreme environments outside the range of tested
environments—a gene-enhanced wheat model
could greatly expand the available information to
help a grower decide among cultivars. Past
attempts to incorporate environmental informa-
tion to explain QTL×environment interactions
have been modestly successful at best (Campbell
et al., 2004).
Gene-enhanced crop models may also help
wheat breeders develop an improved understand-
IMPORTANCE OF TECHNOLOGY
To this point, we have understated the impor-
tance of new technology. Clearly, advances in
technology have drastically changed wheat breed-
ing. The popularity of the bulk breeding method
coincided with the development of the small plot
combine, which can quickly harvest bulk popula-
tions. Breeding for minimum-tillage or no-till
environments is only possible with better, small-
plot drills. Sophisticated experimental designs
and analyses are due to the revolution in comput-
ing power. Similarly, backcrossing for traits
expressed in the adult plant has been greatly
enhanced by molecular markers, which allows
the breeder to select desirable plants for adult
traits at the seedling stage. Wheat breeding
will continue to evolve based upon emerging
technologies.
FUTURE PERSPECTIVES
If the past is prologue to the future, wheat breed-
ing will retain its long-successful methods and
improve them using new technology. While sexual
hybridization will remain the main way for creat-
ing new variation, germplasm developed through
targeting induced local lesions in genomes
(TILLING)(McCallum et al., 2000) will add
precision and effi ciency to the effective use of
mutations. Though currently not available com-
