The bulk method is an inbreeding procedure used to develop self-pollinated crops where seeds from each generation are bulked and randomly mated without selection until advanced generations. In the bulk method, seeds from the F1 to F4 generations are combined in bulk and selection is delayed until later generations when most genetic variation has been reduced. The procedure involves making initial crosses between parent lines, bulk harvesting subsequent generations, and selecting superior lines in later generations for yield trials and cultivar release.

1. Bulk, Pedigree and
Back cross
(continued-Breeding of self pollinated crops)

2.  The bulk method is a procedure for inbreeding a
segregating population until a desired level of
homozygosity is reached. Seed used to grow
each selfed generation is a sample of the seed
harvested in bulk from the previous generation.
 In the bulk method, seeds harvested in the F1
through F4 generations are bulked without
selection; selection is delayed until advanced
generations (F5-F8). By this time, most
segregation has stopped.
A variant method to Mass Selection is the
Bulk Method

3.  Environmental considerations:
 Uses natural selection, therefore its important to avoid
environments that select types not desirable by breeder
 However, natural selection can work for you since it
tends to select for the best adapted, highest yielding
plants.
Breeding Methods in Self-pollinated Crops

4.  Outline of Bulk Method Procedures:
 Season 1: Select most desirable parents; make adequate
number of artificial hybridizations
 Season 2: Plant F1 seed and grow under favorable
conditions; harvest and bulk F2 seed
 Season 3: Plant F2 seed similar to commercial conditions;
harvest F3 seed and bulk
 Season 4-7: Repeat procedures above until F6; then select
individual plants and harvest seed from selections,
keeping seeds separate
Breeding Methods in Self-pollinated Crops:

5.  Outline of Bulk Method Procedures (cont.):
 Season 8: Plant progeny rows of each selection;
select best uniform rows; harvest seed from each
selected row and bulk seed from the row together.
 Season 9-11: Test performance of selections in
replicated trials with standard check cultivars.
 Season 12: Increase line(s) that are superior to
check cultivars; release new cultivar
Breeding Methods in Self-pollinated Crops

6. Bagan Prosedur Metode
Bulk
PROSEDUR METODE BULK
(Poespodarsono, 1988)
Galur A X Galur B
F1 Petak Bulk
F2 Petak Bulk
F3 Petak Bulk
F4 Petak Bulk
F5 Petak Bulk
Selaksi Individu
F6
F7 I I I I I I I I I I I I Penanaman dalam
barisan
F8 I I I I I I I I I Uji Pendahuluan
F9 Uji lanjutan

7.  Bulk Method Advantages:
 Simple
 Needs less labor: Less record keeping than pedigree
 Inexpensive
 Easy to handle more crosses
 Natural selection is primarily for competitive ability
 More useful than pedigree method with lower h2
traits
 Large numbers of genotypes can be maintained
 Works well with unadapted germplasm
 Can be carried on for many years with little effort by the
breeder
Breeding Methods in Self-pollinated Crops

8.  Bulk Method Disadvantages:
 Environmental changes from season to season
so adaptive advantages shift
 Most grow bulk seed lots in area of adaptation
 Less efficient than pedigree method on highly
heritable traits (because can purge non-
selections in early generations)
 Not useful in selecting plant types at a
competitive disadvantage (dwarf types)
 Final genotypes may be able to withstand
environmental stress, but may not be highest
yielding
 If used with a cross pollinated species,
inbreeding depression may be a problem
Breeding Methods in Self-pollinated Crops

9.  How long will a cultivar remain pure?
 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
 To maintain purity, off-types arising from mutation or
out-crossing must be rogued out
Breeding Methods in Self-pollinated Crops

10. Pedigree Selection
Combining the desirable traits of two or more
genotypes in a new improved variety or inbred line.
The keys to successful pedigree selection:
 Detailed record keeping
 Selection of parents
 Typically, one parent is already an
improved locally adapted line.
 The other parent brings one or more
desirable traits that are often well-
expressed.

11. Selection of Parents
 Mean Performance
 Over time and environments; adaptability.
 Genetic Diversity
 Want maximum diversity; geographic
diversity.
 Statistical Performance
 Ability to pass desirable traits to progeny,
early ID of good and bad crosses.

12. Pedigree Selection: Procedures
 Cross selected parents, grow out F1 and self
(manually, if necessary) to obtain F2
 F1 population primarily grown for production of
F2 seed. Rogue out possible selfs; ID of
heterosis
 F2 population is pivotal generation, maximum
genetic variation. Selection intensity ~10% of
most promising; select for components of
complex traits; discard all with major
deficiencies

13. Pedigree Selection
 Self the selected F2’s and grow out progeny rows
of the F3; row-to-row differences begin to appear,
since loci of interest are becoming homozygous
 Higher selection intensity in F3 generation; only
best individuals from a number of families (rows)
are selected; self and keep separate.
 Repeat cycles of selection for phenotype and
progeny row evaluations until F6-8; bulk final
selected families together to form new cultivar

14. Pedigree Selection: Notes
 Maintain records (pedigree) of the phenotypic
characteristics and ancestry of all selections;
selections should represent diverse F2 ancestry;
why records 1st became important
 The number of plants that need to be carried
forward at each cycle depends on:
 the number of traits under selection
 the frequency at which each desirable allele
occurs within the population.
 Dominance among the trait alleles can slow
progress, since homozygous and heterozygous
individuals may not be distinguishable.

15. Pedigree Selection: Advantages
 Eliminates unpromising material at early stages;
 Multi-year records allow good overview of
inheritance, and more effective selection
through trials in different environments;
 Multiple families (from different F2 individuals)
are maintained yielding different gene
combinations with common phenotype
 Allows for comparison to other breeding
strategies

16. Pedigree Selection: Disadvantages
 Most labor, time and resource intensive method;
usually compromise between # crosses and
population sizes;
 Very dependent on skill of breeder in recognizing
promising material;
 Not very effective with low h2
traits;
 Slow; can usually put through only one generation
per year, and the right environmental conditions
must be at hand for accurate selection.
 Upper ceiling set by allelic contents of F2; can not
purge selections of undesirable alleles once
‘fixed’.

17. One solution: Single Seed Descent (Goulden, 1941)
 SSD procedure based on advancing generations
through single seed from each plant in each generation;
 SSD separates the inbreeding phase from the
selection phase - reach the F6 generation faster;
 SSD carries forward maximum number of F2 plants to a
stage near homozygosity;
Basic observation: low response to early
generation selection for complex quantitative
traits due to non-additive effects associated
with high levels of heterozygosity.

18.  Cross selected parents and produce
sufficient F1 seed;
 Grow enough F1 plants to produce 1000-
2000 F2 seed;
 Grow F2 plants under constrained conditions
that force early maturity and harvest 1 seed
form each plant; no observations need to be
recorded;
 Repeat through approximately F5 generation;
Single Seed Descent: Procedures

19.  F5 generation are space planted to produce
seed for F6 progeny row evaluations; can
rogue plants with obvious defects;
 Grow F6-7 progeny rows with standard
cultivar checks; dump poor performers and
rows with residual variation;
 Plant replicated trials and continue as with
pedigree or pure-line selection.
Single Seed Descent: Procedures

20. Single Seed Descent: Advantages
 Rapid generation advance; 2-4 generations/yr
 Requires less space,time and resources in early
stages, therefore accommodates higher # crosses;
 Superior to bulk/mass selection if the desired
genotype is at a competitive disadvantage; natural
selection usually has little impact on population.
 Delayed selection eliminated confusing effects of
heterozygosity; more effective than pedigree
breeding when dealing with low h2
traits;
 Highly amenable to modifications and can be
combined with any method of selection.

21. Single Seed Descent: Disadvantages
 May carry inferior material forward
 Fewer field evaluations, so you lose the
advantage of natural selection
 Need appropriate facilities to allow controlled
environment manipulation of plants for rapid
seed production cycles (day length, moisture
and nutrient control)

22. Backcross Breeding
 Important traditional breeding method for
both self- and cross-pollinated crops
 Consists of the repeated crossing of
progeny with one of the original parental
genotypes (recurrent parent)
 Designed to recreate the genotype of the
recurrent parent plus the desired allele(s)
from the other parent (donor parent; non-
recurrent parent)

23. Backcross Breeding
 Trait of interest should be simply inherited, if
possible and easily phenotyped
 Recurrent parent should be a highly acceptable
genotype (e.g. existing commercial cultivar or inbred
line)
 The best BC donor parent will possess the desired
trait but will not be seriously deficient in other
traits;
 The BC procedure used will depend on the genetic
control of the trait to be transferred, and whether
progeny testing will be needed to identify the
genotype

24. Backcross Breeding
Recovery of the recurrent parent genotype
follows this pattern:
% recurrent % donor
F1 50 50
BC1 75 25
BC2 87.5 12.5
BC3 93.7 6.3
BC4 96.9 3.1
BCm 1-(1/2)m+1
(1/2)m+1

25.  BC-derived lines are expected to be well-
adapted to the environment in which they will
be grown - progeny need less extensive field
testing
 BC line production is repeatable, if the same
parents are used
 If two or more characters are to be
introgressed, these would usually be tracked in
separate BC processes, and the individual
products are combined in a final set of crosses
Backcross Breeding

26.  If the nature of the cytoplasm of the BC-
derived line is critical, the sex of the
recurrent parent must be chosen
accordingly
 Expected recovery of recurrent genotype
slowed by linkage: Linkage Drag
 Rapid method when using greenhouse or
growth rooms
 Requires only small populations; provides
breeder with high degree of genetic control
Backcross Breeding

27. Backcross Breeding: Possible concerns
 BC does not permit extensive gene recombination
 The improved variety differs only slightly from
recurrent parent (e.g. one trait)
 Closely linked deleterious genes may cause
problems
 BC may be difficult to use in some cross-pollinated
species (open pollinated varieties need large
populations to avoid inbreeding depression)
 Environmentally conditioned traits, and multigenic
traits can be a challenge for BC