November 1999 Perishables Handling Quarterly Issue No. 100 Page 10
Top California Varieties
Top Ohio Varieties
Desert Varieties
DNA-marker Group
Similarity Coefficient
- Anchor variety
0
Figure 2. Schematic representation of “cluster analysis”
applied to processing tomatoes. Regionally adapted
varieties fall into distinct groups that guide breeders in
designing efficient crosses and broad selections without
knowing the specific genes involved.
Another practical application, developed at
UC Riverside, is being used to identify seed lot
purity in asparagus. Molecular markers were used
to show that some seed lots used for crown
production contained over 70% poor yielding types
and types with low postharvest quality. This can be
critical information for a perennial crop that is
expected to be productive over a 10-12 year span.
What are theAdvantages of These DNA-based
Fingerprinting Techniques ?
Recent developments have made great progress
towards Faster, Cheaper, and More Reliable. These
specific DNA-based techniques have the following
advantages;
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● Highly reproducible fingerprint pattern
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● Fingerprinting based on DNA can be done at any
stage of plant growth. In comparison, enzyme or
protein-based fingerprinting of traits only found in
flowers or fruit may only be done at that stage of
plant maturity.
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● Only a small amount of plant tissue is needed.
Breeders can make selection determinations at the
seedling stage, for example, and save only those
plants of interest for a whole plant observation.
Larger plant populations may be assessed than
with conventional techniques; or space, time, and
resources may be more economical applied to
variety development.
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● Traits, such as insect and disease resistance, can
be selected by the breeder without having to
depend on the presence of the pest to confirm that
the resistance trait is carried in the varieties.The
expensive and regionally unpredictable field
resistance evaluations can be postponed, with
confidence, until a later stage of variety selection,
closer to commercial release. Variety selections are
not regionally limited, at the early stages, since
issues of plant pest quarantine are removed. No
pest introductions for screening are necessary, as a
simple seedling grow-out is sufficient to monitor
the desired trait.
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DNA-based fingerprinting allows the reliable
tracking of beneficial traits during variety selec-
tion. These have traditionally been difficult or
impractical due to the variable influence of envi-
ronment, plant tissue dependencies ( seed vs. root
vs. leaf vs. fruit etc.), local or regional field condi-
tions, or other factors on enzyme/protein finger-
printing and whole plant visual traits or crop
performance.
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● DNA-based fingerprinting is the only practical or
available technique for ensuring the presence of
multiple beneficial genes in a single variety.
Stable and durable pest resistance strategies that
depend on “stacking” or “pyramiding” resistance
factors, for example, have become much more
attainable with the development of these new
techniques.
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● DNA-based fingerprinting provides the best
currently available technology to establish differ-
entiation for patent protection and Plant Variety
Protection Act Certification.
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● DNA-based marker systems are more readily
automated to increase cost efficiencies.
Automated Marker Systems
Recent advances in “fingerprinting” technology for
multiple markers, 10 to 100 times more efficient
than prior methods, have been applied to corn,
tomatoes, brassicas (the broccoli family), pepper, and
lettuce. The technology is readily automated and
commercial systems are available. Combined with
computer-assisted analysis of the complex pattern,
several hundred DNA marker sites can be generated
per day. Selection for multigene traits, such as
sensory quality, will be greatly aided by these
technology systems. Careful economic analysis is
required for each crop application, as these
approaches are costly. Their use must be justified
relative to the effectiveness of other strategies.