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How to choose parents for a breeding program
- From this, genetic variation is created
- Evaluate strengths and weaknesses
- Evaluate adaptability over environments
- Evaluate combining ability
- Agronomic Traits
- Yield Potential
- Disease Resistance
- End-use Quality
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Where are sources of germplasm?
- Current breeding program
- Regional breeding programs (public and
- private)
- International breeding program
- Landraces
- Wild relatives
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adapted by adapted example of parent selection:
- Don’t worry much about traits such as time to
- flower, maturity, plant height, etc
- Focus in on traits of most importance
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Adapted by unadapted example
- Adapted by Unadapted
- Focus in on the best of the adapted lines
- Agronomic traits start to become more of an
- issue
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How to decide on which traits to select for?
- Traits seen easily in the field
- Heritability of trait
- Availability of molecular markers
- Importance of trait
- Ease of testing (end-use quality)
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how to screen/Identification Traits
- Easily screened and highly heritable
- Can screen in earlier generations
- If predictive, negative selection occurs
- Easily screened and low heritability
- Usually screen later in the breeding process
- (or for multiple rounds)
- Importance of trait will determine how many rounds of selection will need to occur
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Identification of Traits that are hard to screen for:
- Hard to screen and low heritability
- Will be done mid to late generations for
- selection (might need a couple of rounds of
- selection)
- Will look for the use of molecular markers
- Will need larger population sizes
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When to use markers to screen for a trait?
- Trait very difficult to screen for and high on
- breeding objectives
- Biasing populations in favor of a trait
- Need for pyramiding multiple genes into one
- genotype
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Identification of traits hard to screen for and highly heritable:
- Hard to screen and highly heritable
- Will be done in late in selection process
- Again depends on importance of trait and
- resources of group
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Early Screening methods:
- Inexpensive
- Small amount of material
- Non-destructive
- Indirect measures of performance-negative
- selection
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Late screening methods:
- Expensive
- Large amounts of seed/fruit required
- Often destructive
- Direct measures of performance-Positive
- selection
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Describe Early screening:
- Early Generation
- –Number of entries is higher
- –Small quantity of seed required
- –Low genetic variance between entries
- - More difficult to distinguish between
- genetic and random effects
- –Space and labor requirements higher
- –Can eliminate poor performing entries
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Describe Late screening:
- • Late Generation
- –Smaller number of entries
- –Labor requirements still high
- –Positive selection for elite lines
- • Have eliminated poor performing lines
- –Multiple location testing
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Outline experimental design:
- Needs to fairly and effectively evaluate
- genotypes in the field
- Needs to be done in an environment similar to
- that of the farmer
- Need to limit environment to best evaluate
- genetic performance
- Evaluation must be error free
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Sources of error in experimental design:
- Treatments—impose conditions that generate
- variance in outcomes
- Units may be plots, rows, single plants, etc
- Experimental Error is the variation among
- plots that are treated alike
- Soil (site) variability
- – Soil minerals
- – Soil moisture
- – Organic matter
- – Topography and slope
- – Crop rotation/previous crop
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How to reduce error in an experimental design with border rows:
- Use of border rows
- – Competition from outside the plot area
- – Interplot competition
- – Data collected on middle rows only
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How to reduce error in an experimental design with plot size and shape:
- Plot size and shape
- – Dependent upon objectives, stage of breeding,
- resources available, equipment
- – F2 based on individual plant performance so
- plants must be space planted to allow for
- evaluation
- – Mico/mini-plots—inexpensive way of eliminating
- the inferior genotypes
- – Many time rectangular in shape
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How to reduce error in an experimental design with replications:
- Adequate number of replications
- – Replications is critical for statistical analysis
- – Usually 2-4 replications
- – No replications often used in early generations (dangerous!)
- – Number of replications depends on accuracy desired
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How to reduce error in an experimental design when using humans:
- Minimize operator errors
- – Human error
- – Must manage and treat uniformly
- – Data collection must be accurate
- – Mistakes must be accounted for and dealt with
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Experimental Design contin:
- Replication—critical for estimating
- experimental error
- Randomization—Eliminates bias in the
- estimation of treatment effects
- Local control—Use of a known genotype to
- standardize results
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Describe Plot Designs (single plants):
- No design arrangement
- – Usually done in segregating populations
- – Advantages:
- – Inexpensive and easy (large number of genotypes)
- – Limitations:
- – Environmental variations
- – Suitable for traits with high heritability
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Describe Unreplicated Plot Designs (multiple plants):
- Unreplicated
- – Planting single rows or plots for evaluation
- (usually designed to eliminate inferior genotypes)
- – Advantage:
- – Save space and are less expensive
- – Large number of genotypes quickly evaluated
- – Disadvantage:
- – No replications!
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Describe replicated Plot Designs (multiple plants):
- Replicated
- – Randomization important here
- – Complete block—small number of entries, each block contains all entries
- – Incomplete block—large number of entries, genotypes split between blocks to account for variation
- – Advantage:
- – Can account for environmental variation
- – Disadvantage:
- – Can be limited by # of entries and statistics
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