Selection methods in self-pollinated crops

1. Selection Methods in Self
Pollinated Crops
Breeding Principles in self pollinated crops

2. Expected outcomes
• Self-pollinated species have a genetic structure
that has implication in the choice of methods for
their improvement.
• They are naturally inbred and hence inbreeding
to fix genes is one of the goals of a breeding
program for self-pollinated species in which
variability is generated by crossing.
• However, crossing does not precede some
breeding methods for self-pollinated species.

3. Expected outcomes….
• The purpose of this chapter is outline
specific methods of selection for
improving self-pollinated species.
• After studying this chapter, you should be
able to discuss the characteristics,
application, genetics, advantages, and
disadvantages of the following methods
of selection:

4. Selection
A procedure that allows some individuals in the
population to reproduce so that the freq. of the
descendants of these selected individuals increases
in succeeding generations and vice versa.

5. Selection…….
• Only selected individuals are allowed to become
parents of the next generation.
• The strength of selection is expressed as selection
differential (s)
• The proportionate contribution of the offspring's to
next generations is termed as fitness or selective value.
• Due to selection gene freq. in the population changes.

6. Selection Methods in Self Pollinated
Crops
1.Pure line
2.Mass selection
3. Bulk method
4. Pedigree
5. Single Seed Descent (modified pedigree)
6.Backcross

7. Pure Line
Selection

8. Pure line
• Usually no hybridization
• Initial parents (IPs) selected from a
heterogeneous population (i.e.
genetically variable)
• procedure continues until
homogeneity is achieved
• last phase is field testing

9. Pure-line Selection
• A pure line consists of progeny
descended solely by self-pollination
from a single homozygous plant
• Pure line selection is therefore a
procedure for isolating pure line(s)
from a mixed population

10. Pure-line selection
• More effective than mass selection in
development of self-pollinated
cultivars
• However, leads to rapid depletion of
genetic variation
• Genetic variability can be managed
through directed cross hybridizations
• Essential to progeny test selections

11. Pure-line Selection-Steps
Select desirable plants
• Number depends on variation of original
population, space and resources for
following year progeny tests
• Selecting too few plants may risk losing
superior genetic variation
• A genotype missed early is lost forever

12. Steps…..
• Seed from each selection is harvested
individually
• Single plant progen
• y rows grown out
 Evaluate for desirable traits and uniformity
 Should use severe selection criteria (rogue
out all poor, unpromising and variable
progenies)

13. Steps….
• Selected progenies are harvested
individually
• In subsequent years, run replicated
yield trials with selection of highest
yielding plants
• After 4-6 rounds, highest yielding plant
is put forward as a new cultivar

14. Advantages of pure line selection
• Individual of best pure line reflects maximum
genetic advance from a variable population; no
‘poor’ plants maintained
• Higher degree of uniformity
• Selection based on progeny performance is effective
for characters with relatively low heritability

15. Disadvantages of pure line selection
• Requires relatively more time, space, and resources for
progeny testing than mass selection to develop new cultivar
• High degree of genetic uniformity; more genetically
vulnerable and less adaptable to fluctuating environments
• Identifying and multiplication of one outstanding pure-line
depletes available genetic variation;
• Leads to fast genetic erosion

16. How long will a cultivar remain pure?
1. As long as the commercial life of the cultivar,
unless: Seed becomes contaminated with seed from
other sources (e.g. from harvesting and seed
cleaning equipment)
• Natural out-crossing occurs (amount varies by
species but seldom exceeds 1-2% in self-
pollinated crops)
• Mutations occur
2. To maintain purity, off-types arising from
mutation or out-crossing must be rogued out

17. Generalized steps in breeding by pure-line
selection.

18. Mass selection

19. Presentation Title

20. Mass selection
• May or may not include hybridization
• Make IP selections based on single, ideal or desirable
phenotype and BULK seed
• May repeat or go directly to performance testing

21. Functions of Mass Selection
1.Rapid improvement in land-race or mixed cultivars
2.Maintenance of existing cultivars (sometimes purification)