Principles of Plant Genetics and Breeding

Purpose and expected outcomes
As previously discussed, self-pollinated species have a genetic structure that has implication in the choice of methods
for their improvement. They are naturally inbred and hence inbreeding to fix genes is one of the goals of a breeding
program for self-pollinated species in which variability is generated by crossing. However, crossing does not precede
some breeding methods for self-pollinated species. The purpose of this chapter is to discuss specific methods of selection
for improving self-pollinated species. After studying this chapter, the student should be able to discuss the characteristics,
application, genetics, advantages, and disadvantages of the following methods of selection:
1 Mass selection.
2 Pure-line selection.
3 Pedigree selection.
4 Bulk population.
5 Single-seed descent.
And to:
6 Describe the technique/method of backcrossing.
7 Discuss the method of multiline breeding.
8 Discuss the method of breeding composites.
9 Discuss the method of recurrent selection.
Types of cultivars
At the beginning of each project, the breeder should
decide on the type of cultivar to breed for release to producers.
The breeding method used depends on the type
of cultivar to be produced. There are six basic types of
cultivars that plant breeders develop. These cultivars
derive from four basic populations used in plant breeding
– inbred pure lines, open-pollinated populations,
hybrids, and clones. Plant breeders use a variety of
methods and techniques to develop these cultivars.
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Breeding self-pollinated
species
Pure-line cultivars
Pure-line cultivars are developed for species that
are highly self-pollinated. These cultivars are homogeneous
and homozygous in genetic structure, a condition
attained through a series of self-pollinations.
These cultivars are often used as parents in the
production of other kinds of cultivars. Pure-line cultivars
have a narrow genetic base. They are desired
in regions where uniformity of a product has a high
premium.