Bulk Method

• Inbreed in bulk to have homozygous lines
• Select superior lines after F6
• Crosses with no high heritability traits segregating

Points to consider in Bulk Method

1. Natural selection changes gene freq. via natural survival
2. Breeder may assist nature and discard obviously poor types
3. Relieves breeder of most record keeping
4. Most of us treat bulks with extremely low inputs and low expectations.

Note:

• 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.

Advantages of Bulk Method

1. Less record keeping than pedigree
2. Inexpensive
3. Easy to handle more crosses
4. Natural selection is primarily for competitive ability
5. More useful than pedigree method with lower h2 traits
6. Large numbers of genotypes can be maintained
7. Works well with unadopted germplasm
8. Can be carried on for many years with little effort by the breeder

Disadvantages of Bulk Method

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