Principles of Plant Genetics and Breeding

Season 1 Source population C 0
Season 2
Season 3
Bulk seed from
superior progenies;
grow in isolation
Figure 17.2 Generalized steps in breeding by ear-to-row selection.
both steps occurring in one generation. The populations
are created by random pollination of selected
female plants in generation 1. The seed from generation
1 families are evaluated in replicated trials and in different
environments for selection. There are different
kinds of half-sib family selection methods including the
following.
Ear-to-row selection This is the simplest scheme of
half-sib selection applicable to cross-pollinated species
(Figure 17.2).
Applications Half-sib selection is widely used for
breeding perennial forage grasses and legumes. A polycross
mating system is used to generate the half-sib
families from selected vegetatively maintained clones.
The families are evaluated in replicated rows for 2–3
years. Selecting traits of high heritability (e.g., oil and
protein content of maize) is effective.
Procedure
Season 1 Grow the source population (heterozygous
population) and select desirable plants (S 0 )
based on the phenotype according to the
traits of interest. Harvest plants individually.
Keep remnant seed of each plant.
Season 2 Grow replicated half-sib progenies (S 0 ×
tester) from selected individuals in one environment
(yield trial). Select best progenies
and bulk to create progenies for the next
BREEDING CROSS-POLLINATED SPECIES 317
or
C 1 population
Open-pollinate;
select superior plants
Grow progeny rows (half sibs)
Bulk remnant seed from
selected (superior) plants
according to progeny test;
grow in isolation
cycle. The bulk is grown in isolation (crossing
block) and random mated.
Season 3 The seed is harvested and used to grow the
next cycle.
Alternatively, the breeder may bulk the remnant seed
of S 0 plants whose progeny have been selected, and use
that to initiate the next cycle.
Genetic issues The expected genetic gain from half-sib
selection is given by:
∆G HS = [( 1 / 4 )iσ A ]/σ PHS
where σ PHS = standard deviation of the phenotypic variance
among half sibs. Other components are as before.
The tester is the parental population and hence selection
or control is over only sex. The genetic gain is hence
reduced by half (the available additive genetic variance
is also reduced by half because of the control over
the female parent). Genetic gain can be doubled by
selfing each parent to obtain S 1 , then crossing to obtain
half sibs.
Modifications The basic or traditional ear-to-row
selection method did not show much gain over mass
selection. An improvement was proposed by J. H.
Lohnquist in which the creation of family structure,
evaluation, and recombination are conducted in one
generation. The half-sib families are evaluated in