2 HistoryPractice of the pedigree method predates rediscovery of Mendel’s workVilmorin used the pedigree method in France in the 1830’sInstitute at Svalof - used pedigree type breeding in the 1880’s
3 Nillson Represented families by one or more plants Noted that when harvested seed came from only one plant, the progeny were much more uniformCame to call this the “system of pedigree”
4 Begin with the F2 generation May be space planted to provide maximum individual plant expressionMay be planted at the same density as the crop normally is
5 F2 plant selectionIdentify best plants, e.g. short, early, clean, vigorousTag or spray paint plants to signify selectsMay tag at flowering to indicate traits that will not be readable at maturityHistorical - pull or dig up whole plants at maturity to provide plenty of F2:3seed
6 F2 SelectionTo harvest (dig up) single plants or simply harvest single heads is a decision with several implicationsSingle head harvest is much quicker and easier, but it limits the amount of seed and thus the experimental unit that is grown in the F3
7 F2 selection Space-planted or solid seeded - another critical decision Space planted populations allow for individual plant expression, maximum tillering (etc.), and maximum individual plant yieldBut if it does not mirror the way the crop is grown, how “real” is it?
8 Variability Issues Generation Among Within F2:3 1 0.5 F3:4 1.5 0.25 1.750.125F5:61.8750.0625
9 Selection Pressure / No. of Lines Maximize the number of F2:3 lines because the among line variation is greater than the within line variationIf you do not maximize the number of distinct F2:3 families, then you will be relying on within line variation, which is of diminishing magnitude as inbreeding progresses.
11 Selection Pressure / No. of Lines If you have selected only plants from an F2 population, then you will be relying on variation within inbred lines that trace back to those few F2 plants.The problem is that theory tells us that the within line variation will simply not be there.
12 Pedigree InformationThe keeping of pedigree information is very tediousOne rationale for keeping it is to make sure that lines trace back to different F2 plants
13 Pedigree Information Sister lines - what are they? Pedigree information allows us to keep track of sister linesE.g. 1) KY95C and 2) KY95C and 3)KY95C1 and 2 are sisters at the F2:3 level and 1 and 3 are sisters at the F4:5 level
14 Characters for Selection High heritability desirableAmenable to visual selectionTraits that can be evaluated in individual plants or progeny rowsNumber of plants grown must be adequate for number of traits evaluatedMust maintain sufficient number of plants such that variability for low h2 traits like yield still remains.
15 Choice of Environments Assume F2 will be grown in main nursery environment (ex. Lexington)With pedigree selection, early generations will all be grown there because individual plant selection is practicedAlternative is to grow a bulk version of a generation at another location
16 Pros Discard inferior types early Each generation grown in different year which exposes material to different environmentsGenetic relatedness of lines known, so variability among lines retained can be maximized
17 ConsCan’t be used in environments where genetic variability for trait not expressed (off season nursery)Tremendous record keepingMay need experienced person to selectLand and labor intensive
18 Pedigree Selection Most breeders use some aspect of it Few breeders use very strict pedigree selectionToo expensive and labor intensiveMay be most suitable for small program where quality considerations limit size and genetic variability (e.g., malting barley)