Principles of Plant Genetics and Breeding

318 CHAPTER 17
replicated trials in many environments. The approach
was to better manage the environmental and G × E
interactions.
Modified half-sib selection This is a modified version
of the half-sib family selection method.
Applications This method of breeding has been
applied to the improvement of perennial species as previously
indicated for the traditional ear-to-row selection.
It has been used in maize for yield gains of between
1.8% and 6.3% per cycle.
Procedure
Season 1 Select desirable plants from source population.
Harvest these open-pollinated (half sibs)
individually.
Season 2 Grow progeny rows of selected plants at
multiple locations and evaluate for yield performance.
Plant female rows with seed from
individual half-sib families, alternating with
male rows (pollinators) planted with bulked
seed from the entire population. Select desirable
plants (based on average performance
over locations) from each progeny separately.
Bulk the seed to start the next cycle.
Genetic issues The genetic gain has two components –
among ear rows across environments (interfamily selec-
Season 1
Season 2
Season 3
Figure 17.3 Generalized steps in breeding by the full-sib method.
×
Source
population
× ×
tion) and within families (intrafamily selection). The
total genetic gain is given by:
∆G mHS = [( 1 / 8 )iσ A ]/σ PHS + [( 3 / 8 )iσ A ]/σ we
where σ we = square root of the plant-to-plant withinplot
variance. Others components are as before.
Full-sib family selection
Full sibs are generated from biparental crosses using
parents from the base population. The families are evaluated
in a replicated trial to identify and select superior
full-sib families, which are then recombined to initiate
the next cycle.
Applications Full-sib family selection has been used for
maize improvement. A selection response per cycle of
about 3.3% has been recorded in maize.
Procedure: cycle 0
Season 1 Select random pairs of plants from the base
population and intermate, pollinating one
with the other (reciprocal pollination). Make
between 100 and 200 biparental crosses.
Save the remnant seed of each full-sib cross
(Figure 17.3).
Season 2 Evaluate full-sib progenies in multiple location
replicated trails. Select the promising half sibs
(20–30).
Season 3 Recombine the selected full sibs.
Select and cross pairs of
parents (reciprocal crosses)
100–200 plants
Grow replicated
testcross progeny rows
Composite equal amounts of
remnant seed from superior
testcross progeny; grow
in isolated block