Cp population improvement-phenotypic and genotypic (half sib) method

1. Breeding Methods of Cross Pollinated Crops
Genetic Structure of Cross pollinated crops
Comprised of a highly heterozygous and heterogeneous plant population--e.g., AaBbcc:
AABbCc: AaBBcc: etc.
Consequences 1. Shows mild to severe inbreeding depression
2. Progeny from heterozygous plant would be heterogeneous, different from
parents due to segregation and recombination in each generation
Therefore, breeding methods based on
(1)POPULATION IMPROVEMENT Procedures (to avoid inbreeding depression)-INTRA and
INTER population Improvement and
(2) HBRID AND SYNTHETIC VARIETIES.(exploitation of heterosis by production of hybrid
by crossing a variable number of strains selected on the basis of combining ability)
Population Improvement Procedures
• Purposes “ Why”:
a) For maintenance of genetic variability as gene pool
b) As supplement to or replacement of F1 Hybrid
c) As a source of improved parents (inbred) for hybrids
• Principle: To increase the frequency of desirable alleles in the populations which would
result in increase in the frequency of desirable gene combinations or genotypes and the
phenotype of the population would be favorably changed; Interest in over all population
rather than value of individual
• The Recurrent Selection Principle – Recurrent selection is any breeding system to
increase the frequency of desired alleles for particular quantitatively inherited traits by
repeated cycles of selection. A recurrent selection cycle involves
• Identify genotypes superior for a specific trait and
• intermate selected genotypes to produce new gene combinations with improved
expression of the trait.
The amount of progress per cycle will depend on the heritability of the trait for which we
are selecting.
A. population improvement procedures
1. Phenotypic recurrent selection procedures
2. Genotypic recurrent selection procedures
1. Phenotypic recurrent selection procedures
(a) Mass Selection with modification or simple recurrent selection
2. Genotypic recurrent selection procedures (Progeny testing and selection)
(a) Half-sib selection with progeny (Ear to row method)
(b) Half-sib selection with test cross progeny by using broad base tester (Recurrent selection for
GCA)
(c) Recurrent selection for SCA by using simple narrow base inbred in place of broad base tester
(d) Full sib family selection.
(e) Inbred or selfed (S1/S2) family selection.
(f) Reciprocal recurrent selection (Inter population improvement)
B. Hybrids
C. Synthetics and Composites

2. Phenotypic Recurrent Selection (MASS SELECTION)
(without progeny testing)
Ist year (i) Superior plant selected on the basis
(first selection cycle) of phenotype
(ii) open pollinated seed from selected
plants harvested and bulk
2nd year (i) Bulk seed of selected plant grown
(2nd selection cycle) (ii) selection may be repeated
Selection cycle may be Modification:
repeated one or more times Field divided in to small
plots and selection within
plots; composited the seed of
selected plants and raise next
generation to reduce GxE interaction
Yield Trials
OOOOOOO
OOOOOOO
OOOOOO
OOOOOOO
Fig. Mass Selection with modification or simple recurrent selection
Monoecious:
Staminate (Tassel) and
Pistillate (Ear)
inflorescences
OPEN
POLLINATED
FIELD
CONTROLLED
POLLINATION
HALF SIB
FAMILY
FULL
SIB
FAMILY
ONE PARENT COMMON
BOTH PARENTS COMMON
Fig. Half sib and full sib family

3. 1. Genotypic recurrent selection procedures (Progeny testing and selection)
(a) Half-sib selection with progeny (Ear to row method)
Procedure
Season 1 Grow the source population (heterozygous population) and select desirable 50-100
plants 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 from selected individuals in one environment (yield
trial).
Season 3 The population is reconstituted by compositing equal quantities of either (a) seed
harvested from the 5-10 superior progenies or (b) remnant seed from the 5-10 lines with
superior progeny performance. Grow the composite (C1) in isolation with open
pollination to obtain new gene combination.
(b)Half-sib selection with test cross progeny by using broad base tester (Recurrent selection
for GCA)
In this procedure, the selection of the half sib lines to composite is based on test cross
performance rather than progeny performance.
a
a
a
a
a
a
b

4. Procedure A typical cycle of half-sib selection entails three activities –
Season 1 Either (a) Crossing the selected 50-100 plants to pollinate the a common tester and
open pollinate the selected plant or (b) selected plant pollinate the tester and self also
the selected plant.
Season 2 Grow test cross
Season 3 Reconstitute the population (a) by mixing equal quantities of open pollinated seed from
5 to 10 selected plants having superior test cross performance or (b) by mixing equal
quantities of selfed seed from 5-10 selected plants showing superior test cross
progenies. Grow these composite seed in an isolated plot with open pollination to
obtain new population with new gene combination.
Source population
Open pollinated
Superior plant selected
Cross to Self and cross to
Testerplant tester plant
Source population
Open Pollinated
Superior plants selected
Cross to tester parent Self and cross to tester parent
(a) Composite open pollinated
seed from plants with superior
test cross progenies
(b) Composite selfed seed
from plants with superior
testcross progenies
Selected
plant
Tester
parent
Tester
parent
Selected
Plant
Testcross Progeny Testcross progeny
1st
season
3rd
season
Half sib selection with testcross progeny