Transcript chap5 Genetics - Langston University Research and Extension

Forest Genetics And Tree
Breeding
Elements of
Forestry
Kenneth Williams
Fisheries Extension Specialist
Langston University Aquaculture
Extension Program
Problems in Forest Genetics

Large size
 Long life cycle
– 15-20 yrs to sexual maturity

Large land area needed
– Over time may be destroyed by natural
catastrophe
Natural Variation in Populations

Allows trees to adapt to changing
environment
 Increases likelihood of finding individual
trees with economically superior traits.
Continuous vs. Discontinuous
Variation

Discontinuous ex. Seeds red or white
 Continuous ex. Seeds red through many
shades of pink to white. Most colors
clustered around the mean.
 Most tree traits of interest show continuous
variation.
Genetic Variation
Genotype – genetic makeup of an
individual organism.
 Phenotype – external appearance of the
individual.
 Phenotype can be seen and measured.
Genotype usually cannot.

“Nature / Nurture”

What traits are inherited and what traits are
environmentally caused?
Provenance Studies

Seeds from various geographic regions are
grown together in 1 or more locations under
similar conditions that allow a comparison
of the seed sources in order to identify
superior seed stocks.
Provenance Studies

These studies demonstrate that many tree species
are genetically quite variable.
 Certain variations related to climate.
Characteristics changed systematically with
increasing altitude and latitude of seed origin.
 Variation was shown to be in response to
environmental factors. Ex. Growing season and
minimum winter temperature.
Provenance Studies

Adaptation to climate is and other survival
and growth traits are controlled by patterns
of continuous variation.
 Geographic patterns of variation are best
explained by natural selection in response to
environment.
Provenance Studies

Complex adaptations due to competitive
interactions for light , moisture etc.
 Sun leaves and shade leaves.
 Sun leaves - smaller, thicker outer edges of
canopy. More chlorophyll. Shade leaves
opposite.
Shade leave / Sun Leaves


Shade leaves are:
* thinner and weakly lobed
* large surface area
* less support tissue fewer
stomata
*Sun leaves are:
* more xerophytic in nature,
* possess thicker cuticles,
* more and longer palisade
cells
* well developed vascular
tissues.
Origin and Modification of Natural
Variation
Mutations – source of all genetic variation.
Most are harmful.
 Trees not good organism for studying
mutation. Life cycle too long.
 Genetic recombination more common
source of variation.
 Because most trees reproduce sexually,
recombination is an extremely important
evolutionary mechanism.

Migration and Gene Flow As A
Source Of Variation

Migration by way of seed dispersal and
pollination.
 Pollen from outside sources can
contaminate and hinder production of
improved seed.
Random Processes That Modify
Variation

Isolated
populations.
 “founder
effect” –
population
established
by a very
few
individuals.
Directional Modification of
Variation
Principle of selection – there is variability
of organisms.
 Selecting small transmittable differences
over time accumulates until visible
differences appear in the organism.
 Natural selection has no purpose. It is the
consequence of the differences between
individuals with respect to their ability to
produce offspring.

Provenance Selection

Select best stands before selecting
individuals within a stand. Difference
between stands ( groups of trees from a
specific location) can be very great.
Exotic Introduction
Exotic – a plant growing outside of its
natural range.
 Conifers introduced into the southern
hemisphere for timber and fiber
production.
 Often introduced in the search for
disease and pest resistance. Ex.
Eurasian elms introduced in U.S. after
problems with Dutch Elm disease.
 Environmental similarity important
for the success of exotics.

Interspecific Hybrids

Success in forestry is small.
 Greatest use in developing disease and pest
resistant trees.
Plus- Tree Selection

Trees selected from wild populations that
exhibit one or more superior traits.
Comparison – Tree Selection

Tree compared to neighboring trees and is
selected if it exceeds neighbors in traits of
interest.
 Used in Southern, even aged pine stands
where most environmental, age and planting
factors are the same for all trees.
 Does not work well in uneven – aged
stands.
Baseline Selection

Comparing a selected tree to the regional
average. To be selected the tree must exceed
regional average in traits of interest.
What Size Breeding Population?

Large enough to maintain genetic variability
for future.
 Small enough to be cost effective and fit
space available.
 Small enough to make substantial genetic
gains quickly.
 Need a balance of all factors.
Seeds or Scions?
Seeds – original genotype no longer intact.
Each seedling contains a different sample of
the original trees genes plus genes from
pollinating tree.
 Scions – exact genotype of selected tree.
Generally provides greater opportunity for
genetic improvement.

Evaluation Of Select Trees

Wild tree selection serves as first
approximation of individual tree’s genetic
worth.
 Observations over time used to refine
evaluation.
Progeny Testing

Evaluates offspring
of selected trees.
 Trees shown to have
undesirable
genotypes are
eliminated from the
seed orchard.
Genetic Gain

Genetic gain = improvement
 Can be lost if breeding populations are
severely limited. = inbreeding depression.
 Expanding number of stands from which
trees are selected reduces the chance of
inbreeding becoming a problem.
Heritability Estimate

Proportion of variation in the population that is
due to genetic differences among individuals.
 Can be increased by controlling as many
environmental factors as possible. Then selection
from orchard is more likely to be due to genetic
differences.
 Genetic gain from wild-tree selection is about 1020% depending on species and trait selected.
Advanced Generation Breeding

Just beginning to have significant numbers
of 2nd or 3rd generation selected trees.
 Many promises of improvement.
 Many problems associated with F2
generations.
 Lonnnnng term research.
Domesticating The Forest

Natural forests are being
rapidly replaced with native
or exotic trees.
 Monoculture on the rise.
Natural Population Pros

Well adapted to site
 Replacement trees from distant source may
be poorly adapted.
Plantation Forests

May be ecologically unstable in
monoculture. However, some species (ex.
Douglas fir and Jack pine) naturally grow in
monocultures.
 Most concern is not species monoculture
but genetic diversity.
 Most examples of devastated monoculture
systems involve clones.
Plantation Forests

Most objectionable feature to many people
is the visual uniformity of monocultures.
– Even aged stands
– Even spacing
– Same species
Plantation Forests

Solution – mixed species plantings that are
compatible in the plantation system.
Preserving Natural Variation

Need for genetic resource conservation is
widely recognized.
 Original wild population called progenitor
populations. Many have already been lost.
Preserving Natural Variation

Logging and other human activities
have depleted the genetic base of forest
trees.
 High-grading – removing the best trees
from a forest. And monoculture tends to
reduce genetic variability.
 Inadvertent introduction of pests cause
loss of genetic variation. (chestnut
blight and Dutch elm disease.)
Preserving Natural Variation

Parks and National forests may be
used to preserve genetic material.
 Special storage facilities. (Colorado
and in Arctic)
 Breeding orchards and other
collections of trees.
Future Directions

Forecasting human needs for timber 1-2
generations in the future is difficult.
 Large trees are a thing of the past. Trees will
be harvested at increasingly smaller size
and younger age.
 Forest products industries will have to adapt
to changes in tree size.
Future Directions

Gene banks needed in case tree
selections prove to be disastrous
in the future.
 Additional genetic gains appear
to be possible for a number of
generations in the future.
 Ability to stimulate flower
production in juvenile trees will
greatly accelerate breeding and
testing programs.
Biotechnology

Efforts have lagged behind because trees are
slow and difficult organisms to work with.
 Their genetics are poorly understood.
 Economic payoff is slower.
 Will eventually play some part in traditional
breeding programs.
THE END