Principles of Plant Genetics and Breeding

Purpose and expected outcomes
As indicated in Chapter 1, plant breeders want to cause specific and permanent alterations in the plants of interest.
They use various technologies and methodologies to accomplish their objectives. Certain natural processes can also
cause permanent genetic changes to occur in plants. In this chapter, three processes that bring about such heritable
changes – evolution, domestication, and plant breeding – are discussed, drawing parallels among them and pointing
out key differences. After studying this chapter, the student should be able to:
1 Define the terms evolution, domestication, and plant breeding.
2 Discuss the impact of domestication on plants.
3 Compare and contrast domestication and evolution.
4 Compare and contrast evolution and plant breeding.
5 Discuss plant breeding as an art.
6 Discuss plant breeding as a science.
7 Present a brief overview of the plant breeding industry.
Concept of evolution
Evolution is a population phenomenon. Populations,
not individuals, evolve. Evolution is concerned with the
effect of changes in the frequency of alleles within a gene
pool of a population, such changes leading to changes in
genetic diversity and the ability of the population to
undergo evolutionary divergence. Simply stated, evolution
is descent with modification. Proposed by Charles
Darwin in 1859, there are certain key features of the
concept or theory of evolution. Variation exists in the
initial population of organisms, both plants and animals.
As Darwin stated, variation is a feature of natural populations.
More individuals are produced each generation
than can be supported by or survive in the environment.
Environmental stresses place certain individuals in the
population at a disadvantage. The individuals with the
best genetic fitness for the specific environment will
2
The art and science of
plant breeding
survive and reproduce more successfully and become
more competitive than other individuals. The more
competitive individuals will leave more offspring to
participate in the next generation. Such a trend, where
the advantageous traits increase, will continue each
generation, with the result that the population will be
dominated by these favored individuals and is said to
have evolved. The discriminating force, called natural
selection by Darwin, is the final arbiter in deciding
which individuals are advanced. When individuals in
the original population become reproductively isolated,
new species will eventually form.
Patterns of such evolutionary changes have been
identified and exploited by plant breeders in the development
of new cultivars. Scientists have been able to
identify relationships between modern cultivars and
their wild and weedy progenitors. Further, adaptive
variations in geographic races of crops have been