introduction of “exotic,” i.e., agronomically unadapted donor geno-
types into their highbred elite gene pools. The addition or modifica-
tion of single genes to elite lines by genetic engineering would help
to alleviate these difficulties.- Genetic engineering speeds up the breeding process and provides bet-
ter cultivars to farmers and consumers with less effort of labor and
time. There is expectation that the concerted use of biotechnological
methods may substantially shorten the breeding cycle for a given
crop, which presently is in the range of 10–15 years or, for some
woody fruit species, extends to 25 years. This time span appears quite
large if one considers the need for the breeder to adapt his breeding
goals to the rapidly changing requirements by growers, industry,
traders and consumers.
It should be stressed, however, that biotechnological methods such as
genetic engineering are not, and most probably will not become, self-
sufficient in breeding better cultivars. Rather, they may provide addi-
tional tools to the breeder who will still have to apply classical breeding
methods, which continue to constitute the backbone of plant breeding.
The genetic engineering approach relies on (1) a detailed knowledge
of the biochemical pathways that generate the quality trait, (2) the iso-
lation of genes that have an impact on these pathways, and (3) the trans-
fer and expression of one or several of these genes into crops in order
to specifically modify the trait of interest. A number of strategies are
available to genetically engineer a trait.
First, if the plant to be modified expresses a gene leading to unde-
sirable characters, this gene may be shut down by introducing the same
gene once more into the plant but in the opposite direction so that tran-
scription of the native gene is neutralized by its antisense counterpart.
Gene silencing can also be achieved by introducing a truncated version
of the native gene in either direction, a phenomenon that is called co-
suppression. Second, if expression and not suppression of genes is de-
sired, then novel genes that are not originally owned by the plant may
be introduced from any source organism and may be expressed either
constitutively or specifically in a tissue or developmental stage. Finally,
the plant’s own genes may be expressed more abundantly by inserting
additional copies of them or by combining these genes with different
promotors which drive gene expression more efficiently than the gene’s
native promotor.