Bulk method 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? 1

Requirements Two parents –Complementary in strengths and weaknesses AAbb x aaBB 2

Implementation 3 n genotypes in F 2 reduced to 2 n 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 3

Bulk 4 F1 F2 F3 Select among inbred lines Bulk w/o selection F n space plant

Features of Bulk method 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 5

Negative features 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. 6

Single Seed Descent Called “Recombinant Inbred Lines” in molecular marker literature First suggested by Goulden in 1939 and later expanded upon by Brim (a soybean breeder) in

SSD -Requirements Two parents crossed to produce F1 –Exactly like pedigree and bulk 8

Implementation 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 9

SSD systematic inbreeding w/o selection 10 F2 F3 Select among inbred lines Fn

Features of Single seed descent Inbreeding and evaluation of inbred lines Little record keeping Easy to handle populations - extensive field trials not required Final lines represent a “true”sample of variation 11

Negative features of SSD 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 12

Comparison All result in an array of inbred lines 13 Pedigree Select among and within during inbreedin g BulkSSD No selection, assume genes will remain at same frequency Systemati c process to insure that inbred lines represent balanced sample

Pedigree, Bulk and SSD How do they differ in terms of distribution of inbred lines ? 14

Inbred Backcross 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, 51: Develop inbred lines with an array of variation for the quatitative trait 15

Requirements Two parents –Desirable Recurrent parent –Exotic ‘Donor’ parent 16

Implementation 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 17

BC, then inbreed via SSD 18

Features of IBC 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 19

Negative features of IBC 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 20