Agriculture Reference
In-Depth Information
9
Genetic and
Varietal Purity
Testing
Variety Testing - The Twenty-first Century
For the majority of primary agricultural crops, the seed remains the basic delivery system of genetic and
molecular advances to the farmer. The increase in biotech-derived varieties, as well as the many other
changes rapidly occurring in agriculture, has had a direct impact on variety testing. As seeds developed
from biotechnology become more common, and as many of the newly released varieties differ in just one
or a few genes, seed technologists are increasingly being challenged to develop ever more sophisticated and
sensitive genetic purity tests. At the same time, some existing tests are being improved, others are limited
to only speciic crops, while still others have been largely abandoned. Though variety tests are frequently
classiied as traditional and non-traditional, the distinction between those two groups is not always evident.
Isozyme analysis, commonly classiied as a non-traditional biochemical test, has been established and used
for a long time, almost as long as some other 'traditional' quick tests. The same can be said of the ELISA
test, although it has undergone continuous reinement. Many chemical tests continue to evolve and are
still considered reliable and quick methods for routine variety testing. New DNA marker tests share many
common features, the most obvious of which are polymerase chain reaction (PCR) ampliication of DNA
segments and DNA separation by electrophoresis. Variety tests are therefore best classiied according to
their main features and uses rather than an ambiguous grouping into traditional and non-traditional tests.
The continued development of new and improved varieties is the cornerstone of increases in crop yield
and agricultural productivity. By deinition, a variety of a cultivated crop differs from other varieties of the
same species in one or more speciic characteristics. Such characteristics as maturity, lodging resistance,
disease resistance, plant height, and market quality make varieties distinct from one another. Farmers are
vitally interested in the selection of a variety which is best suited to their particular needs because they
recognize that this single decision can have a marked effect on their yields and proit. Varietal identiication
testing is so important that it was the subject of many books (Wrigley, 1995; Henry, 2001; Wesing, 2005)
and several reviews (McDonald, 1998a; Smith and Register, 1998; Cooke, 1984, 1988, 1995, 1998).
When new varieties are developed by plant breeders, a limited amount of seed is increased to quanti-
ties suficient to supply growers' needs. As seeds increase, they must be monitored to ensure that the genetic
purity of the breeder seed is not compromised. The rapid progress in molecular genetics has further led to
an increasing need for new advanced tests to assure the genetic integrity of many new genetically modiied
cultivars. The traditional cultivar purity testing methods using seed or plant morphological traits or even the
This chapter along with many of the images were prepared by Dr. M. B. McDonald for this topic prior to their selec-
tion for inclusion in the AOSA Cultivar Purity Testing Handbook (2008). This, in part, accounts for the use of the
same images in both publications.
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