The important thing to remember about ideotypes, or fitness surfaces, is that both are
dependent on a specific environment. If the environment changes (e.g., if a stress is
added or removed), then the value of an ideotype or the shape of a fitness surface could
change dramatically. A genotype that was near a global peak on the previous surface
may now be in a valley. Given that different agricultural production techniques are really
just different environments, it is not difficult to realize why varieties that were adapted to
one production practice may not be adapted to another. A variety that is short may
produce high yields only when fertilizer is applied, or a variety that does not produce
branches may produce high yields only when planted in high-density stands.
By visualizing plant breeding as a mountaineering expedition on a complex and con-
stantly changing fitness surface, you can easily see why different breeders can have
vastly different approaches and philosophies. Whether a breeder believes that there is a
higher mountain, or not, can determine long-termvs.short-term success.
3.2.10 Other Considerations
Lack of space in this chapter prevents detailed discussion of many additional topics that
make plant breeding challenging and interesting. What follows are some general statements
about additional factors that the interested reader may wish to pursue.
†Some crops exhibitpolyploidy(doubling, tripling, or quadrupling of basic chromo-
some number). This can lead to nondiploid chromosome pairing, which complicates
normal diploid inheritance. Polyploidy can also be induced artificially in order to
create “artificial species” that may be more vigorous, or to combine characters from
two different species.
†Variations in chromosome number (aneuploidy) or chromosome structure (transloca-
tions, inversions, duplications, anddeletions) can affect genetic inheritance. These
phenomena may also be induced artificially for genetic studies.
†Xenia, the expression of pollen genes in the tetraploid endosperm or embryo of a seed,
can complicate the selection of seed traits. Seeds normally show the phenotype of the
parent plant, but carry the genotype of a genetically different offspring.
†Breeders are important stakeholders in efforts to maintain biodiversity throughin situ
andex situcollections of germplasm.
†Interspecific hybridization has been used to transfer alleles controlling traits such as
disease resistance, which may not be present in the normal germplasm of a species.
†Male sterility, and various methods of pollen control, may be useful in the production
of hybrid varieties, but have also been used in normal recurrent crossing programs.
†Plant breeders must manage large amounts of data, and they may need to share data
with other researchers. Electronic data management systems are becoming increas-
ingly important in plant breeding.
†Plant breeders must also be statisticians. There is a large body of literature concerning
the optimization of field plot techniques, and the statistical analysis of test results.
†Resistance to disease is an ongoing battle between plant breeders and the organisms
that cause disease (a variant of the “evolutionary arms race”). Many pest organisms
mutate very quickly, and mutations that overcome new types of resistance are selected
quickly in crop monocultures of a single plant variety. One strategy to overcome this3.2. CENTRAL CONCEPTS IN PLANT BREEDING 61