of quality traits in fruit and vegetables. It should be kept in mind, how-
ever, that virtually all of the present crop varieties with their impressive
level of yield, resistances and quality have been bred by conventional
plant breeding. From the view of the breeder, product quality is but one
of a large spectrum of traits that have to be combined to culminate in a
modern crop cultivar. Since most of the agronomic and quality traits are
oligogenically or polygenically inherited, classical breeding methods like
hybrid breeding, backcrossing or population breeding will continue to
be the major basis of plant breeding in the foreseeable future. Thus, ge-
netic engineering is generally not expected to convert a low-level culti-
var into a market runner. This is illustrated, e.g., by the early ‘FlavrSavr’
tomato variety, which was withdrawn from the market because of its
susceptibility to diseases and rough handling and unsatisfying flavor.
The main task of genetic engineering in plants remains to provide an
added value to an otherwise highbred crop variety. Thus, genetic engi-
neering of crop plants will be able to unravel its full potential only if it
is carefully integrated into classical plant breeding. As a consequence,
since any genetically engineered plant material is withdrawn for one to
several years from the continuous breeding progress that takes place in
classical cultivar development, the “added value” of the transgene(s) has
to be large enough to compensate for this delay and to render transgenic
cultivars competitive with respect to their conventional counterparts. In
the long run, genetically engineered crops will have a large potential of
gaining a premium quality labeling on the market if quality traits of
major public interest such as flavor, avoidance of common allergens or
increased contents of nutraceutically active ingredients are consequently
addressed as breeding goals. Besides monogenically inherited traits, new
technical developments that allow for the transfer of a panel of selected
genes at a time, together with rapidly evolving gene cloning techniques,
will open the way for also targeting the major group of quantitatively
inherited cultivar traits.
REFERENCES
Anonymous. 1995. Position of the American Dietetic Association: Phytochemicals
and functional foods. J. Am. Diet. Assoc.95: 493–496.
Bird, C. R., Grierson, D., and Schuch, W. W. 1994. Modification of carotenoid pro-
duction in tomatoes using pTOM5. U.S. patent 5,304,478.
Burkhardt, P. K., Beyer, P., Wünn, J., Klöti, A., Armstrong, G. A., Schledz, M.,
von Lintig, J., and Potrykus, I. 1997. Transgenic rice (Oryza sativa) endosperm
expressing daffodil (Narcissus pseudonarcissus) phytoene synthase accumu-
References 41