PB Ch 18. Bulk Method of Breeding

• Bulk Method: F2 to F5-F6 generations grown in bulk at commercial densities without individual selection; harvest in bulk; individual plant selection practised in F6 or later.
• Also known as: Mass method, Population method.
• Proposed by: Nilsson-Ehle of Sweden (Svalof) — year approximately 1908-1909
• Modified bulk method: Atkins 

Year

Generation

Action

1

Hybridization

Cross selected parents (simple or complex cross)

2

F1

Space-plant; harvest in bulk (20-100 F1 plants recommended)

3-7

F2 to F6 (Bulk Period)

Grow at COMMERCIAL density (high plant count 30,000-50,000/generation); harvest in bulk each year; NO individual selection; natural selection operates

7 (or later)

F7: Individual plant selection

Space-plant 30,000-50,000 plants; select 1,000-5,000 superior individuals; harvest separately

8

F8: Progeny evaluation

Individual plant progenies in single or multi-row plots; most nearly homozygous; reject weak and inferior progenies; retain 100-300

9

F9: Preliminary yield trial

With commercial check; quality tests; advance superior lines

10-13

F10-F13: Multilocation trials

Standard varieties as checks; lines superior to checks released

14

F14: Seed multiplication

Seed of released variety increased for farmer distribution

Merits

Demerits

Simple, convenient, less expensive — no pedigree records during bulk period

MAJOR LIMITATION: Takes much longer — natural selection important only after F8-F10; bulking to F20+ possible; most breeders avoid bulk for this reason

Each F2 plant equally represented till F6 — no risk of losing good genotypes in early generations

In short-term bulks, natural selection has little effect on population composition

Natural disease/drought selection eliminates undesirable types; increases desirable types — easier isolation of good genotypes

Little opportunity for breeder to exercise skill and judgement in selection

Progenies from long-term bulks superior to short-term selections

Large number of progenies to screen at end of bulk period

More crosses can be handled simultaneously — less labour demand during bulk period

Information on inheritance of characters cannot be obtained (unlike pedigree)

Transgressive segregants more likely to appear in large bulk populations

Natural selection may act AGAINST agronomically desirable types (e.g., dwarf plants shaded by taller plants in dense populations)

S.No.

Pedigree Method

Bulk Method

1

Most widely used breeding method globally

Used to limited extent — mainly barley in USA

2

Individual plants selected in F2 and subsequent generations

F2 to F6 grown in bulk; no individual selection till F7

3

Artificial selection (+ artificial disease epidemics) from F2 onwards

Mainly natural selection during bulk period

4

Natural selection plays NO role — breeder selection only

Natural selection determines population composition during bulk period

5

Pedigree records maintained — time-consuming but informative about inheritance

No pedigree records during bulk period — much simpler

6

12-13 years to release a new variety

15+ years — longer bulk period adds years

7

Requires close attention of breeder from F2 onwards

Little attention required during bulk period

8

Segregating generations space-planted (wide spacing) for individual plant expression

Bulk populations at commercial planting densities — no individual expression needed

9

Smaller population sizes — each line tracked individually

Very large populations (30,000-50,000 plants) recommended

• IFoS 2019 (Q2c, 10M) — Distinguish between Pedigree and Bulk method.
• CSE 2016 (Q7, 20M) — Describe pedigree, bulk and SSD methods.