Principles of Plant Genetics and Breeding

Purpose and expected outcomes
Biological variation is a fact of nature. No two plants are exactly alike. Plant breeders routinely deal with variability
in one shape or form. It is indispensable to plant breeding, and hence breeders assemble or create it as a critical
first step in a breeding program. Then, they have to discriminate among the variability, evaluate and compare
superior genotypes, and increase and distribute the most desirable genotypes to producers. After completing this
chapter, the student should be able to:
1 Discuss the types of variation.
2 Discuss the origins of genetic variation.
3 Discuss the scale of genetic variation.
4 Distinguish between qualitative and quantitative variation.
5 Discuss the rules of plant classification.
Classifying plants
Plant taxonomy is the science of classifying and
naming plants. Organisms are classified into five major
groups (kingdoms) – Animalia, Plantae, Fungi, Protista,
and Monera (Table 5.1). Plant breeders are most
directly concerned about Plantae, the plant kingdom.
However, one of the major objectives of plant breeding
is to breed for resistance of the host to diseases
and economic destruction caused by organisms in the
other four kingdoms that adversely impact plants. Plant
breeding depends on plant variation or diversity for
success. It is critical that the appropriate plant material
is acquired for a breeding program. An international
scientific body sets the rules for naming plants.
Standardizing the naming of plants eliminates the
confusion from the numerous culture-based names of
plants. For example corn in the USA is called maize in
Europe, not to mention the thousands of other names
worldwide.
5
Variation: types, origin,
and scale
Table 5.1 The five kingdoms of organisms as described
by Whitaker.
Monera (have prokaryotic cells)
Bacteria
Protista (have eukaryotic cells)
Algae
Slime molds
Flagellate fungi
Protozoa
Sponges
Fungi (absorb food in solution)
True fungi
Plantae (produce own food by the process of photosynthesis)
Bryophytes
Vascular plants
Animalia (ingest their food)
Multicellular animals