Genetic diversity as a parameter for managing agroforestry systems

Aristotelis C. PapageorgiouForest Genetics Laboratory

Democritus University of ThraceOrestiada, Greece

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plan

- genetic diversity- changes of genetic diversity- genetic system in plant populations

• Agriculture• Rangeland• Forest

- management approach- examples / discussion

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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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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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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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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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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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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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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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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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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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Selection

Some genotypes produce traits that have better chance to lead an organism to survive and reproduce

Higher fitnessThe alleles of this genotype pass easier to the next

generationGenotypes with greater fitness increase / so do their

allelesThe population is adapted to an environment

• Just until it changes...

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Small population size

Not all individuals pass to the next generationNot all gametes successfully mateA fraction of the initial number of individuals (and

alleles) passes to the next generationReduction in numbers (randomly) changes allele

frequencies over time• Rare alleles are easier lost• Small populations lose their diversity

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Ν=10000, p(A)=0,5

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Ν=1000, p(A)=0,5

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Ν=100, p(A)=0,5

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Ν=20, p(A)=0,5

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Genetic bottleneck

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Fragmentation

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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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Hedrick p. 183 up

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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– Finall loss of lethal genes...

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Plant breeding

The creation of new varietiesIn 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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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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Lack of gene flow - fragmentation

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Mutation

Primary source of variationNew allelesRare eventDoes not change frequencies of alleles

much

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The genetic system of a forest

Genetic diversity is maintained when the genetic system is working!

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In agriculture

Fields are ecosystems & production unitsFarming 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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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• Manage at the landscape level

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In rangelands and pastures

Natural ecosystems with large diversityUse natural dynamicsIntroduce proper material (local is safe)Avoid fragmentationAvoid overuse and degradationLandscape level

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Agroforestry systems

Extensive, not intensive use of landLandscape 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 connectivityUse of proper plant material

• Adapted• Variable among units

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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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New approach in forest management

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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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Thank you