Bulk method

1
Bulk method
1

• Bulk is an extension of the pedigree method.
• In contrast to pedigree, early generations are
  grown as bulk populations w/o selection.
• The last generation of bulking, the plants are
  grown as spaced plants
• Bulk is used in self-pollinated species
• What role may natural selection play?

2
Requirements
2

• Two parents
• Complementary in strengths and weaknesses
• AAbb x aaBB

3
Implementation
3

• 3n genotypes in F2 reduced to 2n homozygotes
• Natural selection during bulk phase
• Theoretically, natural selection may result in
  poor genotypes contributing relatively fewer
  seeds to the next generation
• At F5 or F6 space plant for preliminary yield
  evaluations

4
Bulk
4
F1
Bulk w/o selection
F2
F3
Bulk w/o selection
space plant
Fn
Select among inbred lines
5
Features of Bulk method
5

• Inbreeding and evaluation of inbred lines
• Should bulking be done in production environment?
  Natural selection?
• Little record keeping
• Easy to handle populations - harvest in bulk
• Extensive field trials not required

6
Negative features
6

• Maximum productivity is established in F2
  generation
• No recombination among superior lines
• Objective is an array of inbred lines which have
  been inbred from an F2 population, but, how
  natural selection, migration, mutation and drift
  may have shifted the population is unknown.

7
Single Seed Descent
7

• Called Recombinant Inbred Lines in molecular
  marker literature
• First suggested by Goulden in 1939 and later
  expanded upon by Brim (a soybean breeder) in
  1966.

8
SSD -Requirements
8

• Two parents crossed to produce F1
• Exactly like pedigree and bulk

9
Implementation
9

• Objective is rapid inbreeding to evaluate inbred
  lines
• Easy way to maintain populations
• Often minimum space required
• Inbreeding can be done in greenhouse or winter
  nursery

10
SSDsystematic inbreeding w/o selection
10
F2
F3
Fn
Select among inbred lines
11
Features of Single seed descent
11

• Inbreeding and evaluation of inbred lines
• Little record keeping
• Easy to handle populations - extensive field
  trials not required
• Final lines represent a truesample of variation
  

12
Negative features of SSD
12

• Maximum productivity is established in F2
  generations
• No recombination among selected lines
• Must evaluate large numbers of inbred lines to
  identify superior ones
• Little opportunity for early generation
  selection, as inbreeding may be done in
  greenhouse or winter nursery

13
13
ComparisonAll result in an array of inbred lines
Pedigree
Bulk
SSD
Systematic process to insure that inbred lines
represent balanced sample
Select among and within during
inbreeding
No selection, assume genes will remain at same
frequency
14
14
Pedigree, Bulk and SSD How do they differ in
terms of distribution of inbred lines ?
15
Inbred Backcross
15

• Combines features of Backcross and SSD
• Generally used in crosses with exotic germplasm
• The goal is to identify major genes involved in
  quatitative variation (Wehrhan and Allard,
  Genetics 1965, 51109-119.
• Develop inbred lines with an array of variation
  for the quatitative trait

16
Requirements
16

• Two parents
• Desirable Recurrent parent
• Exotic Donor parent

17
Implementation
17

• P1 Adapted parent x P2 Donor parent
• BC1 (P1 x F1) 25 exotic
• BC2 (P1 x BC1) 12.5 exotic
• BC3 (P1 x BC2) 6.25 exotic
• Thus, BC before initiating SSD

18
BC, then inbreed via SSD
18
19
Features of IBC
19

• Incorporate exotic germplasm
• Final evaluation based on inbred lines that
  represent a range of variation for quantitative
  trait.
• Can be done in GH or winter nursery

20
Negative features of IBC
20

• Maximum productivity is established in BC
  generations
• No recombination among lines
• Little opportunity for selection
• Often used in genetic studies vs. breeding
• Must evaluate many inbred lines