return of the american chestnut - university of maryland...the return of the american chestnut tree...
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The Return of the American The Return of the American The Return of the American The Return of the American The Return of the American The Return of the American The Return of the American The Return of the American
Chestnut Tree (Castanea dentata)Chestnut Tree (Castanea dentata)Chestnut Tree (Castanea dentata)Chestnut Tree (Castanea dentata)Chestnut Tree (Castanea dentata)Chestnut Tree (Castanea dentata)Chestnut Tree (Castanea dentata)Chestnut Tree (Castanea dentata)
Gary P. Carver, PhD
www.carverscarvings.com
� Six species of chestnut trees
� Several species of Asian and North American
chinquapins
� All hybridize to some degree
� All in the Fagaceae family, which includes beech
(Fagus) and oak (Quercus)
Chestnut Classification Chestnut Classification –– CastaneaCastanea
2
Castanea Leaf Identification (L to R): American Chestnut (C. dentata),
Chinese Chestnut (C. mollissima), Chinkapin (C. pumila), European
Chestnut (C. sativa), and Japanese Chestnut (C. crenata). 3
Castanea Nut Identification (L to R): American, Chinese, Japanese,
European
4
� Dispersal and evolution of Castanea from Asia to Europe to North America.
� Chloroplast DNA sequences suggest a common Castanea ancestor originated
in Asia about 40 – 60 million years ago.
� Castanea dentata probably diverged from C. sativa in the late Eocene epoch –
approximately 35 million years ago.
Castanea Castanea Migration Pathway Migration Pathway
5
Historic Historic
Natural Natural
Range of Range of Castanea Castanea
dentatadentata
6
Old Growth Old Growth
GiantGiant
Southern Appalachians
7 8
The Redwood The Redwood
of the Eastof the East
9
The King of the The King of the ForestForest
Abandoned Log Cabin – Shenandoah
National Park
Mountain Charcoal Hearth
Split Rails - Worm Fence
Historic Historic
Forest Forest
ResourceResource
10
Chestnut Harvest
Street Vendor
Chestnuts Are Good FoodChestnuts Are Good Food
11
1904: Disease Pandemic 1904: Disease Pandemic –– Identification Identification
of Chestnut Blight from Asiaof Chestnut Blight from Asia
� “Parasitic” fungus - Cryphonectria parasitica
� Enters bark and infects cambium, not roots
� Rapid and uncontrollable dispersal
12
13Ghost ForestGhost Forest
Spread of Spread of
Cryphonectria Cryphonectria
parasiticaparasitica
14
Sunken CankerSunken Canker
Swollen CankersSwollen Cankers
15 Coppicing Coppicing –– Response to StressResponse to Stress 16
American Chestnut American Chestnut TodayToday
� Minor component of the under story
� Few trees flower or grow large
� “Mother tree” orchards help preserve genetic diversity
� May disappear without intervention
17
Environmental Requirements of Environmental Requirements of
American Chestnut TreesAmerican Chestnut Trees
� Slightly acid (pH 5.5), well-drained soil
� Sunlight
18
Environmental Enemies of American Environmental Enemies of American Chestnut TreesChestnut Trees
� Fungi (cryphonectria parasitica, phytophthera cinnamomi)
� Browsers (deer)
� Grazers (cows)
� Borers (Asian ambrosia beetles)
� Egg layers (Asian gall wasps, chestnut weevils)
19
� Ecological and environmental benefits
� Economic value: wood and nuts
� Reforestation benefits: � Fast growing (suited for clear cuts)
� Tolerant of relatively acidic and dry soils (suited for strip-mined land),
� Coppices (resulting in less need for replanting)
� Educational opportunities
� Moral imperative
Why Restore the American Why Restore the American Chestnut Tree?Chestnut Tree?
20
1. Backcross breeding
2. Intercrossing large survivors
3. Genetic modification
4. Hypovirulence
5. The “Phil Rutter genetic storm”
6. Natural evolution
Paths to Blight ResistancePaths to Blight Resistance
21
� The American Chestnut Foundation (TACF) backcross breeding program uses resistance from Castanea mollissima (Chinese chestnut species common in United States)
� Three stages of backcross breeding; six generations in 30 years
� Intercross American and Chinese chestnuts to make an F1
� Backcross F1 to pure Americans three times
� Intercross third backcross trees two times
� Assumption: three “incompletely dominant” genes convey resistance
Path 1. Backcross BreedingPath 1. Backcross Breeding
22
Backcross Breeding Backcross Breeding
ProgramProgram
Chinese
F1 ½ American (50%)
AmericanX
American
BC1 ¾ American (75%)
X
American
BC2 7/
8American (88%) American
BC315/
16American (94%)
X
X
BC3
BC3 F215/
16American (94%)
X
BC3 F2
BC3 F315/
16American (94%)
X
� Each generation select for:
� Blight resistance
� American characteristics
� Initial Product: true-
breeding American type
with a high level
of blight resistance23
First Generation: HybridizationFirst Generation: Hybridization
AmericanAmerican ChineseChinesex
100% American 0% AmericanNo Resistance Full Resistance
F1F1
50% American
Moderate Resistance
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F1 x American50% American 100% American
Moderate Resistance No Resistance
B175% American
Moderate Resistance
American100% American
No Resistance
B287.75% American
Moderate Resistance
x
American100% American
No Resistance
B393.75% American
Moderate Resistance
x
7
25
Resistance in the F1 and Backcross Resistance in the F1 and Backcross
GenerationsGenerations
rrr
RRR RrRrRr 3R
RRr RrRrrr 2R
rRR rrRrRr 2R
RrR RrrrRr 2R
Rrr Rrrrrr 1R
rrR rrrrRr 1R
rRr rrRrrr 1R
rrr rrrrrr 0R
No offspring can be homozygous for full resistance in
these generations.26
B3
93.75% American
Moderate Resistance
x B3
93.75% American
Moderate Resistance
B3F2
93.75% American
Fully Resistant
B3F2x
93.75% American
Fully Resistant
B3F393.75% American
Fully Resistant
Initial Seed for Reforestation
and Distribution
8
27
RRR RRr rRR RrR Rrr rrR rRr rrr
RRRRRRRRR RRRRRr RrRRRR RRRrRR RRRrRr RrRrRR RrRRRr RrRrRr
RRrRRRRrR RRRRrr RrRRrR RRRrrR RRRrrr RrRrrR RrRRrr RrRrrr
rRRrRRRRR rRRRRr rrRRRR rRRrRR rRRrRr rrRrRR rrRRRr rrRrRr
RrRRRrRRR RRrRRr RrrRRR RRrrRR RRrrRr RrrrRR RrrRRr RrrrRr
RrrRRrRrR RRrRrr RrrRrR RRrrrR RRrrrr RrrrrR RrrRrr Rrrrrr
rrRrRrRRR rRrRRr rrrRRR rRrrRR rRrrRr rrrrRR rrrRRr rrrrRr
rRrrRRRrR rRRRrr rrRRrR rRRrrR rRRrrr rrRrrR rrRRrr rrRrrr
rrrrRrRrR rRrRrr rrrRrR rRrrrR rRrrrr rrrrrR rrrRrr rrrrrr
One cross should be homozygous for all resistance genes, and many homozygous for one or two resistance genes.
Resistance in the Intercross Resistance in the Intercross GenerationsGenerations
28
Staminate Catkins – Male Flowers
Dried Pollen Applied From Vials
Bisexual Catkins – Female and Male
Controlled Pollination Controlled Pollination –– Breeding Monoecious TreesBreeding Monoecious Trees
Pollen Bags Prevent Open Pollination
Staminate Catkins – Male Flowers Bisexual Catkins – Female and MaleStaminate Catkins – Male Flowers Bisexual Catkins – Female and Male
29
Controlled Pollination In the FieldControlled Pollination In the Field
30
Growing Backcross ChestnutsGrowing Backcross Chestnuts
MDTACF has 15 orchards with over 5000 trees
31
� Chestnut blight fungus introduced to the stem of a tree
� Inoculation identifies the trees suitable for producing future crosses
� 1st step in determining blight resistance in backcross chestnuts
� Backcross chestnuts should range from highly susceptible to
moderately resistant to blight infection
� Intercross chestnuts should range from moderately susceptible to
highly blight resistant
Resistant canker
Susceptible canker
Inoculation With the Blight FungusInoculation With the Blight Fungus
32
� Look at EP155 (high virulence) and SG2-3
(moderate virulence) cankers on all trees
� Score based on size of each canker: 1 = good
resistance, 5 = little or no resistance
� Of those trees showing acceptable resistance,
also rate American character based on 15
traits
� Select those few trees showing moderate
resistance and good American character for
further breeding
� Remove all other trees from the breeding line
Evaluating Inoculation ResultsEvaluating Inoculation Results
33
Inoculating Inoculating
Trees With Trees With BlightBlight
1. Bore hole in cambium
2. Insert cultures
3. Seal with tape
34
1 year post-inoculation
Resistance Rating: 5
SG 2
3
EP 155
EP 155
35
Resistance Rating: 2.5
1 year post-inoculation 2 years post-inoculation
SG 2-3
EP 155
36
Timeline for Timeline for
RestorationRestoration
� 2005: harvest first B3F3 nuts
� 2008: plant B3F3 nuts in field trials
� In Maryland 2012: planted B3F2 nuts in our first seed orchard
� Large scale restoration will take decades—or centuries
� Questions:
� How will trees be introduced into existing ecosystems?
� How will we measure success?
37
breeding
testing reintroduction
Restoration—
a continuous process
38
Path1. (Cont.) Backcross BreedingPath1. (Cont.) Backcross Breeding
� The Connecticut Agricultural Experiment Station
(Sandra Anagnostakis) backcross breeding program uses Castanea crenata (Japanese
chestnut) resistance
� Dr. Anagnostakis has already produced B3F3’s
with Japanese heritage
� MDTACF plans to intercross Chinese and Japanese-heritage B3F3s to determine whether
this will produce a more robust resistance
39
Path 2. Intercrossing Large SurvivorsPath 2. Intercrossing Large Survivors
� The American Chestnut
Cooperators Association provides
“cooperators” nuts from large survivors. The association’s main
priorities are
� Development of an all-
American blight resistant
chestnut tree� Biological control of the blight.
� The hope is that any small native
American chestnut resistance will be reinforced
40
Path 3. Genetic ModificationPath 3. Genetic Modification
� New York State chapter of TACF using transgenic micro propagation to produce blight-resistant American
chestnut trees
� Incorporate plant blight-resistance-enhancing
genes� First introduced gene: oxalate oxidase (from wheat)
� “Plantlets” take 2 years from laboratory to field
� 31 different “vector constructs” (target gene or
genes and selectable marker genes) being grown
� Different promoters used to create a variety of “gene constructs”
� Thousands of field-growing transgenic trees have
begun screening for blight resistance41
Other BioOther Bio--Technology AdvancesTechnology Advances
� New leaf assay technique using molecular markers
being tested for early screening� Chestnut genome mapping has begun
� Experiments to insert hypoviral DNA into blight
fungus
� Hybrids grown to evaluate new sources of resistance from Chinese chestnut trees (Castanea henryi and
Castanea seguinii)
42
� Besides increasing the resistance of the trees, it is
possible to decrease the virulence of the fungus
� Natural soil and plant viruses (“hypoviruses”) are
known to infect the blight fungus and weaken it
� Orchard chestnut trees in Europe are inoculated with
hypoviruses
� Hypovirulence often promotes infection by other soil
organisms, which tends to be beneficial to the tree
(“cruddy bark”)
Path 4. HypovirulencePath 4. Hypovirulence
43 “Clopper Lake” tree with “cruddy bark” and no visible blight fungus stromata 44
Almost all the
large survivors in Maryland are
“cruddy bark”
trees, like this
one at Sugarloaf
Mountain
45 46
� Hypovirulence can be cytoplasmic or nuclear
� Cytoplasmic hypovirulence spreads only via
infected bark
� Nuclear hypovirulence can also be spread by spores
� Vegetative incompatibilities limit spread of
cytoplasmic hypovirulence
� Upwards of 64 vegetative compatibility types identified in North America
� As a result, cankers must be converted to
hypovirulence individually
More About HypovirulenceMore About Hypovirulence
47
Path 5. The Path 5. The ““Phil Rutter Genetic StormPhil Rutter Genetic Storm””
� “Plant everything—let them
fight it out”
� “If It’s Not Dead, DON’T KILL
IT”
� “If there’s lots of fungus growing, something will show
up to eat it”
48
Path 6. Natural SelectionPath 6. Natural Selection
� Might have already worked if millions of trees had not been cut down in advance of the blight
� Today, deer and development are major barriers
to the spread of blight-resistant chestnut trees
� The forest is not the same as it was before the chestnut blight, making natural reintroduction of
chestnut problematic
� Maples, oaks and hemlocks have filled the gap
� Invasives (e.g., stilt grass) have changed the forest floor
� Natural spread of hypovirulence may occur
49
An F1 (dentata x
mollissima) growing
in a grove of six others in
Mechanicsville, MD
50
� I thank you all for listening
� I hope you learned interesting things about
American chestnut trees
� I hope you are anxious to see them return
Final SlideFinal Slide
301-831-9151
www.carverscarvings.com
51