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The Pedigree Method

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

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The Pedigree Method

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  1. The Pedigree Method

  2. 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

  3. 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”

  4. Begin with the F2 generation • May be space planted to provide maximum individual plant expression • May be planted at the same density as the crop normally is

  5. F2 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 F2:3seed

  6. F2 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 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 yield • But if it does not mirror the way the crop is grown, how “real” is it?

  8. Variability Issues

  9. 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.

  10. Selection Pressure / No. of Lines • If you have selected only 5 - 10 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.

  11. 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 F2 plants

  12. Pedigree Information • Sister lines - what are they? • Pedigree information allows us to keep track of sister lines • E.g. 1) KY95C - 100 - 14 -23 - 8 - 6 - 0 and 2) KY95C - 100 - 14 -25 -2 - 2 - 0 and 3)KY95C - 100 - 14 -23 - 8 - 12 - 0 • 1 and 2 are sisters at the F2:3 level and 1 and 3 are sisters at the F4:5 level

  13. 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 h2 traits like yield still remains.

  14. 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

  15. 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

  16. 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

  17. 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)

  18. Fulhio / Purkof /3/ Trumbull // Hope / Hussar /5/ Fairfield /4/ PI94587 /3/ Hungarian // Fultz / Hungarian /8/ LaPorte /7/ Minhardi / Wabash /5/ Fultz / Hungarian // Illinois No. 1, W38 /3/ Wabash /4/ Fairfield /6/ Redcoat / Wisconsin 245 / Afghanistan /9/4* Knox /8/( Purdue 5127 ) Kawvale /5/ Fultz / Hungarian // Illinois No. 1, W38 /3/ Wabash /4/ Fairfield /6/3* Trumbull // Hope / Hussar /7/ Knox sib /5/ Fairfield /4/ PI94587 // Fultz / Hungarian /3/ Fultz / Hungarian / 10 /2* Knox / Frex // Riley sib. Pedigree of Compton Wheat

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