Lecture 13-2

  1. What is a synthetic cultivar?
    —advanced generation of cross-fertilized (random mating) seed mixture of parents that may be strains, clones, or hybrids
  2. Generality of breeding synthetics:
    •  Parents are based primarily on GCA
    •  Propagated for a limited number of generations then must be reconstituted from the parental stocks
  3. Desirable Features of breeding synthetics:
    •  Yield reduction in advanced generations minimal
    •  May become better adapted to region over time
    •  Genetically heterogeneous
    •  Stability over changing environments
  4. Polycross testing for GCA:
    50-100 clones are planted so that each clone has the same random chance of being pollinated by other pollen sources
  5. Topcross testing for GCA:
    —selected clones are grown in alternate rows with a open-pollinated cultivar as a tester
  6. Diallel cross
    —achieves all possible single crosses involving all parents testing for GCA:
  7. Polycross breeding procedure:
    •  Year1: several thousand plants screened to identify superior
    •  Year2: 100-200 selected and selective pressure imposed
    •  Year3: Polycross nursery tests GCA
    •  Year4: Polycross progeny test and select 5-10 clones with highest performing progeny  Year5: Clones are propagated and intermated
    •  Year6: syn-0 increased to produce syn-1 seed
    •  Year7: released as cultivar
  8. General features of synthetic cultivars:
    • 100-200 genetically superior yet diverse plants are allowed to randomly intermate to generate seed for commercial use.  
    •  Bees cross-pollinate plants at random  
    •  Synthetic cultivars are highly diverse, non-uniform populations
  9. Synthetic genetic issues:
    •  The syn-1 generation is highest performing, subsequent generations show a decline in trait values (although not as much as hybrids)
    •  Additive gene action is considered more important than dominance genotypic variance  
    •  Synthetic cultivars exploit the benefits of both heterozygosity and heterosis
    •  Natural selection changes the genotypic composition of synthetics (if alfalfa seed in California is used for production in Midwest, winter hardiness might be lost)
    •  The genetic composition of the population changes after each generation of crosspollination.
    •  Populations are not stable like inbred lines or hybrids.
  10. Considerations when breeding synthetics:
    •  Number of parental lines used (5-6 is optimum).  Too few lines and the decline of heterosis between generations increases
    •  High mean performance of parental lines reduces the reduction in performance between generations (non-inbred parents)
    •  The higher the mean syn-1 value, the more acceptable the syn-2 value will be.
  11. Asexual synthetic reproduction:
    Asexual Kentucky bluegrass –faculative apomictic most of seed produced is carbon copy of mother plant w/o fusion of male and female gametes.  Ploidy level can vary and chromosome numbers vary from 28-150
  12. Sexual synthetic reproduction:
    Cross pollinated -most turfgrasses are obligate outcrossers. Heterosis is preferred for yield. Many grasses tetraplpoid/diploid with self incompatibility mechanisms
  13. List the Methods used by Turf Breeders
    • 1. Recurrent Selection
    • 2. Mass Selection
    • 3. Paired crosses
    • 4. Polycrosses
    • 5. Cell tissue culture
    • 6. Mutation breeding
    • 7. Collecting
    • 8. Serendipity
  14. Nuts and Bolts of synthetic planting:
    •  Field space-planted on 2 ½ foot centers
    •  Sections relate to different species/projects
    •  Each row is 20 plants
    •  Each row represents 1 family line of ½ siblings from seed or turf sprigs
    •  To see variability within lines typically 5-10 rows planted per line
    •  Isolation required between projects/compatible species
Card Set
Lecture 13-2
plant breeding