Principles of Plant Genetics and Breeding

Comments
Generation
Year 1 P 1 × P 2
Year 2
Year 3
Year 4
Year 5
Year 6
Year 7
Year 8
F 1
F 2
F 3
F 4
F 5
F 6
F 7
Years 9–11 F 8–F 10
Figure 16.5 Generalized steps in breeding by bulk selection.
1 Space planting of the F 1 will increase the yield of F 2
seed.
2 The breeder may screen the bulk population under
different natural environments in a rotation (e.g., soil
condition – salinity, acidity; disease resistance; temperature
– winter kill, etc.). There may be an increase
in broad adaptation of the cultivar. However, care
should be exercised to avoid the evaluation of plants
under a condition that could eliminate genotypes
that are of value at different sets of environmental
conditions.
3 Screening for photoperiodic response is desirable and
advantageous in the early stages to eliminate genotypes
that are incapable of reproducing under the environmental
conditions.
BREEDING SELF-POLLINATED SPECIES 295
Number
of plants
50–100
2,000–3,000
2,000–3,000
2,000–3,000
3,000–5,000
300–500
30–50
10
1
Action
Bulk and space plant F 1
Bulk and plant at
commercial seeding rate
Bulk and plant at
commercial seeding rate
Bulk and plant at
commercial seeding rate
Space plant; select
superior plants
Select and establish family
rows from plants or heads
Conduct preliminary
yield trials
Conduct advanced yield
trials
Cultivar release
4 Natural selection may be aided by artificial selection.
Aggressive and highly competitive but undesirable
genotypes may be physically rogued out of the population
to avoid increasing the frequency of undesirable
genes, or to help select benign traits such as seed
color or fiber length of cotton. Aiding natural selection
also accelerates the breeding program.
5 The degree of selection pressure applied, its consistency,
duration, and the heritability of traits, are all
factors that impact the rate at which unadapted segregates
are eliminated from the bulk population.
Genetic issues
Applying the theories of population genetics (see
Chapter 7), repeated self-pollination, and fertilization
will result in three key outcomes: