Principles of Plant Genetics and Breeding

Purpose and expected outcomes
Physiological processes are common to all plants. However, there are morphological and physiological differences
among plants. Morphological and anatomical traits are products of physiological processes. Yield is the ultimate
goal of a plant breeding program. It is the product of complex biochemical processes. Plant breeders rarely select solely
on yield without regard to some morphological trait(s). After completing this chapter, the student should be able to:
1 Define yield.
2 Discuss the biological pathway to economic yield.
3 Discuss the concept of yield potential.
4 Discuss the concept of yield plateau.
5 Discuss the concept of yield stability.
6 Discuss breeding of lodging resistance.
7 Discuss breeding of shattering resistance.
8 Discuss breeding of plant stature.
9 Discuss breeding for early maturity.
10 Discuss breeding of photoperiod response.
Physiological traits
Plant growth and development depend on a complex
interaction of biochemical and physiological processes.
Plant physiological processes are under genetic control
as well as under the influence of the environment.
The genotype of the plant determines the total complement
of enzymes in the cell and hence is a determining
factor in plant growth. As D. C. Rasmusson and
B. G. Gengenbach stated, physiological gene functions
determine the manner and extent of the genotypic contribution
to the phenotype of the plant. Physiological
gene action also reflects gene differences that provide
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Breeding for
physiological and
morphological traits
the basis for selection of desirable genotypes in plant
breeding.
The major physiological processes are photosynthesis,
respiration, translocation, and transpiration. Crop yield
and productivity depends on the proper functioning of
these processes. These traits are quantitatively inherited.
Physiological traits may be broadly defined to include
the major physiological processes, and yield and its components.
It also includes plant environmental responses
(to photoperiod and environmental stresses). Some of
the specific physiological traits that have been bred by
plant breeders with varying degrees of success are photosynthetic
rate, leaf angle, leaf area, stomatal frequency,