Principles of Plant Genetics and Breeding

Purpose and expected outcomes
As previously indicated, plant breeders depend on variability for crop improvement. Plant genetic resources (plant
germplasm) used in plant breeding are natural resources that are susceptible to erosion from use and abuse. It is
important that they be collected, properly used, managed, and conserved to avoid irreparable loss of precious genetic
material. After completing this chapter, the student should be able to:
1 Discuss the importance of germplasm to plant breeding.
2 Define the types of germplasm.
3 Discuss the sources of germplasm for plant breeding.
4 Discuss the mechanisms for conservation of germplasm.
5 Discuss the international role in germplasm conservation.
Importance of germplasm to plant breeding
Germplasm is the lifeblood of plant breeding without
which breeding is impossible to conduct. It is the genetic
material that can be used to perpetuate a species
or population. It not only has reproductive value, but
through genetic manipulation (plant breeding), germplasm
can be improved for better performance of the
crop. Germplasm provides the materials (parents) used
to initiate a breeding program. Sometimes, all plant
breeders do is to evaluate plant germplasm and make a
selection from existing biological variation. Promising
genotypes that are adapted to the production region are
then released to producers. Other times, as discussed in
Chapter 5, breeders generate new variability by using a
variety of methods such as crossing parents, mutagenesis
(inducing mutations), and, more recently, gene transfer.
This base population is then subjected to appropriate
selection methods, leading to the identification and further
evaluation of promising genotypes for realease as
cultivars. When breeders need to improve plants, they
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Plant genetic resources
for plant breeding
have to find a source of germplasm that would supply
the genes needed to undertake the breeding project.
To facilitate the use of germplasm, certain entities
(germplasm banks) are charged with the responsibility
of assembling, cataloguing, storing, and managing large
numbers of germplasm. This strategy allows scientists
ready and quick access to germplasm when they need it.
Centers of diversity in plant breeding
The subject of centers of diversity was first discussed
in Chapter 2. Whereas the existence of centers of
crop origin or domestication is not incontrovertible, the
existence of natural reservoirs of plant genetic variability
has been observed to occur in certain regions of the
world. These centers are important to plant breeders
because they represent pools of diversity, especially wild
relatives of modern cultivars.
Plant breeding may be a victim of its own success.
The consequence of selection by plant breeders in their