—advanced generation of cross-fertilized (random mating) seed mixture of parents that may be strains, clones, or hybrids
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
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
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
Topcross testing for GCA:
—selected clones are grown in alternate rows with a open-pollinated cultivar as a tester
Diallel cross
—achieves all possible single crosses involving all parents testing for GCA:
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
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
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.
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.
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
Sexual synthetic reproduction:
Cross pollinated -most turfgrasses are obligate outcrossers. Heterosis is preferred for yield. Many grasses tetraplpoid/diploid with self incompatibility mechanisms
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
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