A lecture about genetic diversity and its applications and importance for agroforestry systems

1. Genetic diversity as a parameter for
managing agroforestry systems
Aristotelis C. Papageorgiou
Forest Genetics Laboratory
Democritus University of Thrace
Orestiada, Greece

2. plan
- genetic diversity
- changes of genetic diversity
- genetic system in plant populations
• Agriculture
• Rangeland
• Forest
- management approach
- examples / discussion
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5. Important things about
biodiversity
 Is of complex nature and finds its full meaning in
complex cases (e.g. landscapes and multiple
levels of organization)
 Involves different perceptions of its meaning and
importance
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6. Genetic component of biodiversity
 ...is a total of meaningless mathematic
expressions…
 Perlman & Adelson 1997
 …should not be given priority, since its
measurement is complicated and expensive…
 Dobson 1995
 Misunderstandings:
 “Laboratory analysis is the first step of any gene
conservation or management measure”
 “The object of conservation and management
programmes are the genes we see in the
laboratories”
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7. So, what is genetic diversity?
 The differences among organisms that can be
inhereited
 Passing from one generation to the other = mating
 Changes over time = evolution
 Is the basis of all other levels of biodiversity
 Underestimated and under-represented
 Measured by:
 Field observations (environment? / P=G+E)
 Lab observations (practical relevance?
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8. Field observations
- morphometry
• Environmental or genetic?
• Multivariable statistics
• Landmarks
- common environment (trials)
• Provenance / progeny tests
• Traits of practical relevance
– Growth, survival, resistance...etc.
• ANOVA
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9. Lab observations
- previously: chromosomes, visible traits, enzymes
- nowadays: polymorphism at DNA level
• Fragments (fragment length)
• Sequencies of nucleotides
• Some more sofisticated things...
- no direct relevance with traits
• This changes however
- frequencies of genotypes and alleles
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10. The population
- central concept to genetics
- a set of individuals
• Mating (same species – or not?)
• Same place (more or less)
- demography
- frequency of alleles and genotypes
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11. Alleles and genotypes
- allele: variant of the same gene that does
the same job, just differently
• Mendel had yellow and green peas (gene
= pea color / alleles = green and yellow)
• A diploid organism can have up to two
different alleles at each gene
- genotype: the types of alleles at a gene
• Homozygote: two copies of the same
allele
• Heterozygote: two different alleles
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12. Importance of genetic diversity
 Main condition for adaptation under new
environments
 Maintenance of populations and species
 Stability of communities and ecosystems
 Constant production of goods and services
 Biological information base
 Is transferred over generations and rearranged
through mating system
 Influenced by population size
 Changes and promotes adaptation
 Is imported and exported
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13. Evolution
Changes of allele or genotype frequencies
over time and/or space
• Selection / adaptation
• Small population size / genetic drift
• Non-random mating / inbreeding
• Migration / gene flow
• Mutation
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15. Selection
Some genotypes produce traits that have better
chance to lead an organism to survive and
reproduce
Higher fitness
The alleles of this genotype pass easier to the next
generation
Genotypes with greater fitness increase / so do their
alleles
The population is adapted to an environment
• Just until it changes...
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17. Small population size
Not all individuals pass to the next generation
Not all gametes successfully mate
A fraction of the initial number of individuals (and
alleles) passes to the next generation
Reduction in numbers (randomly) changes allele
frequencies over time
• Rare alleles are easier lost
• Small populations lose their diversity
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18. Ν=10000, p(A)=0,5
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19. Ν=1000, p(A)=0,5
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20. Ν=100, p(A)=0,5
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21. Ν=20, p(A)=0,5
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22. Genetic bottleneck
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23. Fragmentation
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24. Non random mating
Random mating
• Equal probability of all mating events
• Keeps frequencies of alleles and
genotypes stable
• Equilibrium
Non random mating – inbreeding
• Decreases heterozygotes
• Increases the appearence of lethal genes
• Inbreeding depression
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25. Hedrick p. 183 up
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26. Self – pollination / selfing
Most severe form of inbreeding
• Results in full homozygosity in 6 / 7
generations
• Reduces heterozygotes by 1/2 every
generation
In natural plant populations
• Dissadvantage in outbreeding species
• However, most species self pollinate
• Evolutionary advantage under stable
environment
– Stability of traits
26 – 13/07/11of lethal genes...
Finall loss

27. Plant breeding
The creation of new varieties
In agriculture
• Self pollination creates “pure breeds”
• Absolutely homozygous
• Stable in artificial environment
In forestry
• Self pollination is avoided
• Reduces heterozygosity and fitness
• More complex and variable environment
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28. Migration – gene flow
Migration of individuals (seeds) or gametes
(pollen)
• New alleles arrive aqnd increase diversity
• Adaptation may be delayed
Ideal situation: small levels of gene flow
allow diffrentiated adaptation and
maintenance of high diversity levels
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30. Lack of gene flow - fragmentation
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31. Mutation
Primary source of variation
New alleles
Rare event
Does not change frequencies of alleles
much
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32. The genetic system of a forest
Genetic diversity is maintained when the genetic system is working!
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33. In agriculture
Fields are ecosystems & production units
Farming requires uniform conditions and uniform
material (one genotype)
• Pure lines
• Hybrids
How to increase genetic sustainability?
• Change the scale!
• See the broader picture
• Use of local & adapted varieties
• Uniformity in the field, not among fieldsI
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34. In Forest Management
Natural populations on variable sites
• Great diversity
Maintaining genetic diversity
• Avoid disturbance of the genetic system
• Use natural regeneration dynamics
• Avoid fragmentation and small
populations
• Proper / adapted reproductive material
See the broader picture
34 • Manage at the landscape level
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35. In rangelands and pastures
Natural ecosystems with large diversity
Use natural dynamics
Introduce proper material (local is safe)
Avoid fragmentation
Avoid overuse and degradation
Landscape level
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36. Agroforestry systems
Extensive, not intensive use of land
Landscape level management
• Keep diversity within and – most important – among
landscape elements and among landscapes
Maintain dynamics of nature
• Natural cycles
• Genetic system of plants
Avoid fragmentation – establish connectivity
Use of proper plant material
• Adapted
• Variable among units
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37. Strategies
 Forest management
 Secure pollen & seed movement
 Promote natural regeneration
 Expand management in non productive forests
– This includes rangelands
 Landscape connectivity
 Sustainable use of rangelands
 Improvement through proper material
 Restoration
 Local seed or best adapted seed
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38. New approach in forest
management
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39. Adaptive conservation &
management
 Ex situ: to preserve current genetic
structures for future needs
 Frequent collection of reproductive material
for plant species
 Restore in gene banks
 Keep in plantations in different locations
 Seed orchards for restoration purposes
 Adaptive breeding
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40. Thank you
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