Presentation on theme: "The Pedigree Method. History Practice of the pedigree method predates rediscovery of Mendel’s work Vilmorin used the pedigree method in France in the."— Presentation transcript:
The Pedigree Method
History Practice of the pedigree method predates rediscovery of Mendel’s work Vilmorin used the pedigree method in France in the 1830’s Institute at Svalof - used pedigree type breeding in the 1880’s
Nillson Represented families by one or more plants Noted that when harvested seed came from only one plant, the progeny were much more uniform Came to call this the “system of pedigree”
Begin with the F 2 generation May be space planted to provide maximum individual plant expression May be planted at the same density as the crop normally is
F 2 plant selection Identify best plants, e.g. short, early, clean, vigorous Tag or spray paint plants to signify selects May tag at flowering to indicate traits that will not be readable at maturity Historical - pull or dig up whole plants at maturity to provide plenty of F 2:3 seed
F 2 Selection To harvest (dig up) single plants or simply harvest single heads is a decision with several implications Single head harvest is much quicker and easier, but it limits the amount of seed and thus the experimental unit that is grown in the F 3
F 2 selection Space-planted or solid seeded - another critical decision Space planted populations allow for individual plant expression, maximum tillering (etc.), and maximum individual plant yield But if it does not mirror the way the crop is grown, how “real” is it?
Variability Issues GenerationAmongWithin F 2: F 3: F 4: F 5:
Selection Pressure / No. of Lines Maximize the number of F2:3 lines because the among line variation is greater than the within line variation If 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.
Selection Pressure / No. of Lines If you have selected only plants from an F 2 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.
Pedigree Information The keeping of pedigree information is very tedious One rationale for keeping it is to make sure that lines trace back to different F 2 plants
Pedigree Information Sister lines - what are they? Pedigree information allows us to keep track of sister lines E.g. 1) KY95C and 2) KY95C and 3)KY95C and 2 are sisters at the F 2:3 level and 1 and 3 are sisters at the F 4:5 level
Characters for Selection High heritability desirable Amenable to visual selection Traits that can be evaluated in individual plants or progeny rows Number of plants grown must be adequate for number of traits evaluated Must maintain sufficient number of plants such that variability for low h 2 traits like yield still remains.
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 practiced Alternative is to grow a bulk version of a generation at another location
Pros Discard inferior types early Each generation grown in different year which exposes material to different environments Genetic relatedness of lines known, so variability among lines retained can be maximized
Cons Can’t be used in environments where genetic variability for trait not expressed (off season nursery) Tremendous record keeping May need experienced person to select Land and labor intensive
Pedigree Selection Most breeders use some aspect of it Few breeders use very strict pedigree selection Too expensive and labor intensive May be most suitable for small program where quality considerations limit size and genetic variability (e.g., malting barley)