Lecture 13-2

—advanced generation of cross-fertilized (random mating) seed mixture of parents that may be strains, clones, or hybrids

•  Parents are based primarily on GCA
•  Propagated for a limited number of generations then must be reconstituted from the parental stocks

•  Yield reduction in advanced generations minimal
•  May become better adapted to region over time
•  Genetically heterogeneous
•  Stability over changing environments

50-100 clones are planted so that each clone has the same random chance of being pollinated by other pollen sources

—selected clones are grown in alternate rows with a open-pollinated cultivar as a tester

—achieves all possible single crosses involving all parents testing for GCA:

•  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

• 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

•  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.

•  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.

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

Cross pollinated -most turfgrasses are obligate outcrossers. Heterosis is preferred for yield. Many grasses tetraplpoid/diploid with self incompatibility mechanisms

• 1. Recurrent Selection
• 2. Mass Selection
• 3. Paired crosses
• 4. Polycrosses
• 5. Cell tissue culture
• 6. Mutation breeding
• 7. Collecting
• 8. Serendipity

•  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