Future Prospects - Genetics, Genomics and Breeding of Crop Plants - page 323

On one hand, the massive sequence data will offer access for developing
DNA markers for genes controlling economically important traits. These
markers will be useful for rapidly moving genes among elite lines to enhance
the target traits via marker-assisted breeding. Marker-assisted selection
evolved from the idea of indirect selection, which has been a common practice
in both plant and animal breeding. For two highly correlated traits, selection
imposed on trait A will result in a genetic gain for trait B. Similarly, if a
visible morphological trait is affecting or associated with a desirable
economical trait like high yield, this visible morphological trait will be useful
as a marker for selecting to increase yield. However, for a given species, the
number of visible and stable morphological markers is limited. In sunflower
the anthocyanin pigment gene ( T ), which was tightly linked to a nuclear
male sterile gene ( Ms 10 ), was proposed by Leclercq (1966) to be used as a
marker for utilizing genetic male sterility for hybrid production. When
isozyme markers were used to reveal genetic polymorphism in plants,
Tanksley and Rick (1980) applied the isozyme markers to tomato breeding
and proposed to use them in other crops.
With the advent of DNA-based markers, marker-assisted selection
became a reality for many important crop species. It has proven to be a
powerful tool for incorporating target genes into a recipient line at an
accelerated pace. Following the same trend of other crops, sunflower
researchers have applied marker-assisted selection to improve this crop.
Marker-assisted selection is the primary level for application of molecular
markers to breeding because only one or a few single-gene controlled traits
are targeted and low throughput techniques are used. The secondary level
is marker-assisted breeding in which a large number of qualitative and
quantitative traits are targeted and a high throughput genotyping facility is
required. The highest level for application of molecular markers to breeding
will be breeding by design, a fairly new concept which aims to optimize all
allelic variation for all genes governing traits of economic importance. The
achievement of such optimization will depend on a combination of precise
genetic mapping, high-resolution chromosome haplotyping and extensive
phenotyping (Peleman and van der Voort 2003). The practice of breeding by
design in sunflower waits for more available genetic information and
genomics tools to be developed in the near future.
On the other hand, the sequence data will enable scientists to determine
the genetic and molecular bases of agriculturally important genes through
massively parallel genetic analysis on microarray chips. Once a gene
conditioning a given trait is identified, it is possible and relatively easy to
replace, suppress, or otherwise modify that gene to achieve an ideal
phenotype through genetic engineering.
Up to now, there has not been commercial production of transgenic
sunflower. This has been due to two major concerns. The first relates to the