Principles of Plant Genetics and Breeding

Purpose and expected outcomes
Plants are plagued by a host of insects and pathogens that often must be controlled or managed in crop production.
To control a parasite effectively requires an understanding of its biology, epidemics, spread, and the damage it
causes. A variety of methods are used in pest control, each with advantages and disadvantages. These methods are
chemical, biological, cultural, legislative, and physical controls. A specific tactic in the method of biological pest control
is the use of disease-resistant cultivars in crop production. Breeding for disease and insect resistance is one of the
primary objectives in plant breeding programs. After completing this chapter the student should be able to:
1 Discuss the economic importance of plant pests.
2 Discuss the genetic basis of disease resistance.
3 Compare and contrast resistance breeding strategies.
4 Discuss the role of wild germplasm in disease- and insect-resistance breeding.
5 Discuss specific applications of biotechnology in plant breeding to control pests.
6 Discuss disease epidemics and their breeding implications.
Groups of pests targeted by plant breeders
Plant diseases are caused by pathogens that vary in
nature and may be microscopic or readily visible (e.g.,
virus, plant, animal). These pathogens may be airborne
or soil-borne. Six general groups of causal agents of disease,
which represent six general approaches to breeding
for pest resistance, may be identified as: airborne fungi,
soil-borne fungi, bacteria, viruses, nematodes, and
insects. Through an understanding of the biology, epidemics,
spread, and damage caused by these organisms
in each category, breeders have developed certain strategies
and methods for breeding cultivars to resist certain
types of biotic stress in plant production.
It should be pointed out that plant breeders have
devoted varying amounts of resources to breeding for
resistance in these categories with varying degrees of
success. Plant species vary in their susceptibility to
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Breeding for resistance to
diseases and insect pests
diseases caused by pathogens or pests in each group.
Some crop production pests are conspicuously absent
from the list because they are relatively unimportant
(e.g., mites) or are not practical to breed against (e.g.,
birds).
Cereal crops tend to have significant airborne fungal
disease problems, while solanaceous species tend to
experience viral attacks. Diseases that afflict crops of
world importance and cause major economic losses
and are readily transmitted across geographic boundaries
receive funding from major donors. Breeding
for resistance to fungi, especially airborne fungi, is
the most prominent resistance breeding activity. N. W.
Simmonds has suggested that the relative importance
of the six groups of pathogens of importance to
plant breeders, might be something like this: airborne
fungi > soil-borne fungi > viruses > bacteria = nematodes
= insects.