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Physiological v. Morphological
- Physiological—processes common to all plants
- photosynthesis, translocation, transpiration, leaf angle, water utilization, harvest index
- Morphological—products of physiological processes
- Yield, plant height, maturity, flowering date
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Yield
- Most important aspect of plant breeding
- Composed of many important physiological and morphological traits
- What traits are these?
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What is biological yield?
the total dry matter produced per plant or per unit area
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What is economic yield?
- the total weight per unit area of a specified plant product that is of marketable value
- Corn-both ear and stalk of value
- Sugar beet-all plant parts of value
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How to enhance yield:
- Seasonal adaptation
- Tolerance to adverse environmental factors Pest and Disease resistance
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What are the components of yield?
- Can be difficult to breed directly for yield Components are easier to select for
- Plants per unit area
- Tillers per plant
- Number of ears per plant
- Number of seeds per ear
- Compensation can occur in some circumstances
- Wheat and tiller number
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What is Yield Potential?
the inherent optimum capacity to perform under a given environment
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What is Yield Stability?
no G x E interactions
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What does yield plateau?
- Less focus on yield and more on disease resistance
- Increases in fertilizer prices
- Genetic potential is present
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What is Lodging resistance?
- resistance to leaning, bending, or breaking of the plant prior to harvest
- Short stature
- Stronger, thicker stalks,
- Resistance to stalk/stem pests
- Recurrent Selection
- Molecular markers
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What is Shatter Resistance
- Shatter-fruits split open upon maturity and discharge their seeds
- Advantageous in the wild, not in cultivation
- Of high economic importance
- Breeding is often done by visual selection Also subject to environmental conditions Hail, wind, etc.
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Why is reduced plant height desirable?
- Reduced stature increases harvest index
- Less straw desired only in some instances Selection mainly done visually
- Genetics fairly well understood in many crops
- Played role in the green revolution
- GA sensitive and insensitive types
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Long-day plants:
- require a light period longer than a certain critical length in order to flower
- Wheat, barley, alfalfa, sugar beet
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Short-day plants:
- —require a photoperiod of less than a certain critical length
- Corn, rice, soybean, peanut, sugarcane
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Day-neutral:
- plants will flower regardless of the duration of day length
- Desirable when producing crop over latitudes
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Photoperiod Response:
- Need plant to flower at the correct time to maximize yield potential
- Genetics highly understood
- Breeding done both visually and with markers
- Need a firm understanding of the environment one is breeding for before selecting for photoperiod response
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Breeding for Resistance:
- A high priority for many breeding programs Yield potential can never be reached if pests are a limiting factor
- Various breeding methods and strategies have been developed
- Main disease will vary greatly by type of crop one is breeding for
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Disease Biological and Economic Effects:
- Complete plant death
- No economic return and weed issues
- Stunted growth
- Typical of viruses
- Partial plant death
- Usually when adult plants are attacked
- Direct product damage
- High economic damage
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Disease control methods:
- Exclusion of the pathogen from the host
- Reduction of the pathogen’s inoculum
- Improvement of host resistance
- Protection of the host Chemicals
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Disease Concepts:
- Pathogenecity The capacity of the pathogen to cause a disease
- Virulence The extent of disorder or disease development
- Disease triangle Pathogen—Host—Environment
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Plant disease defense:
- Pre-existing defense mechanism
- Morphological features that post as barriers Secondary metabolites
- Infection-induced defense mechanism
- Upon infection host produces chemical products
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Plant disease defense Avoidance:
- Reduces the probability of contact between pathogen and host
- Time of planting
- Morphological traits
- Allelochemicals
- Odors
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Plant disease defense Resistance:
- Manifests after the host has been attacked by the pathogen
- Passive resistance—mechanism is preexisting
- Active resistance–the mechanism is induced
- Hypersensitive reaction-prevents pathogen establishment
- Overdevelopment of tissue-excessive abnormal growth such as galls or leaf curling Underdevelopment of tissue-afflicted part becomes stunted or underdeveloped
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describe tolerance:
- Ability of plant to maintain economic yields while under attack from pest
- Plant vigor
- Rapid root growth
- Photosynthate partitioning
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What is Vertical Resistance
- Race or pathogen specific
- Single gene or qualitative resistance
- Typically absolute in reaction
- Typically termed non-durable resistance
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What is horizontal Resistance
- Race-non-specific
- Multiple genes/minor genes (quantitative) Minor gene reactions
- Typically termed durable resistance
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Resistance Breeding Strategies I:
- Breeders typically only focus on pests of major economic importance
- Ease and level of success varies greatly
- Consistency in screening of high concern Instability of pest may require constant selection of new resistance mechanisms
- Must justify breeding for pest (the process is long and expensive) Natural resistance is not always available Level of success varies from one pest to another (foliar pathogens easier than root pathogens)
- Instability of pest resistance modifies the host (it is what keeps us in business)
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Resistance Breeding Strategies II:
- Gene pyramiding
- Planned release of resistance genes
- Multilines
- Breeding with vertical resistance
- Combining vertical and horizontal resistance
- Role of wild germplasm
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Resistance Breeding Procedures:
- Identification of resistance genes
- Either through literature or own efforts
- Transfer of these genes into germplasm
- Backcross, forward breeding, markers
- Consistent reliable screening
- Field screening, greenhouse screening
- Selection
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