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Chestnut Research Milestone Achieved at Penn State's
Arboretum
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In the first test of blight resistance
in the hybrid chestnut orchard in The Arboretum at Penn
State, two strains of chestnut blight fungus were inserted,
one in each of two small holes in the trunks of seedlings
planted in 2002. |
The hybrid chestnut orchard in The Arboretum at Penn State was
inaugurated on
June 24, 2002, as part of a ceremony establishing the partnership
between The Pennsylvania State University's College of Agricultural
Sciences and The American Chestnut Foundation (TACF). The mission
of TACF is to create a blight-resistant variety of American chestnut,
using a breeding plan developed by the organization’s founders,
and restore the species to its native range within the woodlands
of the eastern United States. The orchard is the final stage of
the breeding program and represents the efforts of countless volunteers
who contributed their time and efforts to this mission.
Until a century ago, the American chestnut was one of the most
abundant tree species in eastern North America. The species was
valued highly for its wood and for the food it provided to both
humans and wildlife. Unfortunately, the species was virtually
eliminated from the wild during the first several decades of the
20th century by an introduced fungal pathogen to which American
chestnuts had little resistance. Today wild chestnut trees survive
only as short-lived stump sprouts that rarely flower and seldom
produce fruit.
"We are extremely happy to forge this cooperation between Penn
State and TACF through the establishment of this plantation in
the Arboretum," says Kim Steiner, Arboretum director. "The American
chestnut was once the dominant tree species in Pennsylvania, so
it is extremely important for us to be working toward restoring
the species. Penn State has three scientists participating in
chestnut research through the support of the Robertson Family
Endowment for the Reestablishment of the American Chestnut and
an endowment from the Louis W. Schatz Center for Tree Molecular
Genetics."
Source: Howard Nuernberger Marshall Case, left,
executive director of The American Chestnut Foundation,
and Robert Steele, dean
of Penn State's College of Agricultural Sciences, watch
as Herb Darling, president
of The American Chestnut Foundation, signs the memorandum
of understanding that documents Penn State's partnership
with the foundation (June 24, 2002). |
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The chestnut trees in Penn State's orchard are fifth-generation
hybrid chestnut, containing approximately 95% American chestnut
characteristics (on average). The hybrids were derived through
a backcross-breeding program that began with a crossing of American
with Chinese chestnut. The Chinese chestnut was used due to its
high resistance to chestnut blight (Cryphonectria parasitica).
Subsequent generations were then backcrossed with American chestnuts
to regain the American chestnut “type” in combination
with Chinese resistance genes.
It is thought that two or three genes control blight resistance
in chestnut. Parents of the orchard trees each had blight resistant
alleles from their paternal parents and susceptible alleles from
their American “mothers.” When two of these trees
are intercrossed, one out of 64 of its progeny will be homozygous
for resistance (assuming three genes control resistance). Homozygosity
is necessary since blight resistance is incompletely dominant.
According to Timothy Phelps, the research technologist working
on this project, “To ensure that we get at least one individual
that is homozygous for blight resistance we will plant 150 seeds
from each cross of a mother and a father tree. Statistically,
this should give us two blight resistant offspring trees, and
we will choose the one with morphological characteristics that
most closely resemble American chestnut.”
To ensure biodiversity of both American and blight resistant
characteristics, Penn State will plant one replication of 150
seeds from 30 families (i.e. genotypes) bred on TACF’s research
farm in Meadowview, Virginia, plus nine replications of 150 seeds
from 20 families bred through the Pennsylvania Chapter of TACF’s
regional breeding program. Following this procedure will ultimately
result in planting 31,500 trees on the orchard grounds. Keeping
just one tree from each replication will result in 210 seed orchard
trees that are homozygous for resistance, thus ensuring that all
of their progeny are also homozygous for resistance. These progeny
will then be used to begin reintroducing the American chestnut
to its native range. Breeding work will continue in order to expand
the genetic base and strengthen "American" characteristics
of the restoration trees.
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The block of seedlings in this photo
contains the seedlings that were planted in 2002. Only 1
in 64 will be able to survive the inoculation. It is hoped
that these few will produce blight-resistant seed for field
tests throughout the Mid-Atlantic region. |
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The 257 seedlings planted in 2002 at Penn State represent four
TACF families. Routine maintenance of the seedlings involves frequent
watering and fertilization soon after transplanting, as well as
keeping the neighboring vegetative competition down through mowing,
weeding, and mulching. The Pennsylvania Department of Conservation
and Natural Resources’ Bureau of Forestry kindly provided
materials and installation of a deer exclosure around the initial
planting area.
The orchard will continue to grow larger each year as more parent
trees from the fourth generation reach maturity and begin intercrossing.
Within five to ten years, the most promising of the families planted
throughout the first few years will have been selected and will
be producing the initial seed for restoration.
Source: Howard Nuernberger Robert Steele, dean
of Penn State’s College of Agricultural Sciences;
Kim C. Steiner, director of The Arboretum
at Penn State and professor of forest biology; R.
Alexander Day, nursery operations manager at Penn
Nursery in the Bureau of Forestry in the Pennsylvania Department
of Conservation and Natural Resources; and John
Oliver, secretary of the Pennsylvania Department
of Conservation and Natural Resources, discuss chestnut
research efforts and reforestation plans using the blight-resistant
chestnut. |
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Eventually TACF hopes to build on Penn State's involvement in chestnut
research by establishing an office in the Education Center at the
Arboretum to provide technical assistance for regional breeding
efforts in Pennsylvania, New York, New England, and possibly other
northeastern states.
"In our agreement with Penn State, we have a goal to assign two
staff members to the Arboretum," says Marshal Case, director of
the foundation. "One would work on the ongoing science of dealing
with the blight leading up to the reforestation plans for the
chestnut, and the second would be an outreach position to work
with our other state chapters in the northern Appalachian region."
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Source: Pennsylvania
Chestnut Tree Blight Commission
The healthy American chestnut trees in this photograph once
grew in Crawford County, Pennsylvania. |
The foundation operates a research farm in Virginia and is headquartered
in Vermont. A nonprofit organization, it has approximately 5,000
members nationally and 600 in Pennsylvania. The trees planted
at the Arboretum are the outcome of TACF breeding efforts begun
in 1983 using pedigreed, hybrid material created by U.S. Department
of Agriculture breeders back in the 1940s.
In 2003, Penn State field-planted greenhouse seedlings from seven
new families of Pennsylvania origin, which represent one line
of blight resistance. Of 313 planted, 306 survived, resulting
in a 98% survival rate. Also, an additional 274 Meadowview seedlings
were transplanted which completed the existing sub-plots begun
in 2002. Altogether during this past year, the plantation was
home to 826 chestnut trees, which is about 2.5% of all of the
trees that will be planted over the life of the plantation (31,500)--a
small, but healthy start.
During winter 2004, funding for an eight-foot tall, woven-wire
deer exclosure fence
that encompasses the entire plantation was provided by grants
from the Hardwood
Forestry Fund and the National
Tree Trust awarded through The American Chestnut Foundation.
In spring 2004, Penn State expanded the orchard by planting 188
seeds and 155 seedlings, all of Pennsylvania origin.
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Source: Timothy Phelps
This picture, taken in spring 2004,
features seedlings that were planted in the Arboretum in
2002. |
As of spring 2005, there were over 2,000 trees growing in the Arboretum
seed orchard, which has reached only six percent of its capacity.
Volunteers expanded the orchard on April
21, 2005, by planting 700 chestnut seeds.
Inoculating Seedlings with Chestnut
Blight
A milestone in the program was reached on Wednesday, June 8, 2005,
at 9:00 a.m. when a group of volunteers in the Pennsylvania Chapter
of TACF (PA-TACF) inoculated the oldest seedlings (planted in 2002
and pictured above) with two strains of the chestnut blight fungus
(Cryphonectria parasitica). Inoculation involved wounding
the tree and inserting the fungus into the wound. Penn State will
be able to determine the level of resistance of the tree based on
the tree's response to the wound. Initial selections of breeding
stock will be made this year, followed by final selections next
spring.
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 Tape
was applied to each wound after the fungus had been inserted
in order to prevent the fungus from drying out, and to prevent
other contaminants from entering the wound. |
Statistically, one out of 64 should breed homozygous for blight
resistance. When two selected plants are crossed, all of their
progeny will breed true for resistance. Controlled crosses could
be made as early as next year if selections have been made and
the plants are flowering. It may, therefore, be possible to harvest
a few blight-resistant chestnut seed in October of 2006.
Rating Blight Resistance (November 2005)
By fall, all 232 inoculated trees had developed the cankers that
verify the presence of the disease. PA-TACF volunteers measured
the length and width of these cankers and rated the trees for relative
resistance to the blight on a scale of 1 to 5. (A tree with a rating
of "1" has the smallest cankers and is considered highly
resistant.) On November 18, Tim Phelps, the research technologist
who maintains the orchard, cleared all trees that had not shown
enough blight resistance to merit further testing. A brief video
of this process, called "rogueing," more information about
the selection criteria, and a table showing the results of the initial
selection are available on the College of Agricultural Sciences'
Chestnut
Growers' Web site.
In May 2006, Sara Fitzsimmons, tree breeding program coordinator,
will lead a crew in choosing the best of the surviving trees (probably
10 to 15) for production of blight-resistant seed.
For more information about this research project, please contact
Kim Steiner at (814) 865-9351 or steiner@psu.edu.
You may also wish to visit The
American Chestnut Foundation for more information about their
efforts to restore the American chestnut to its former place in
our Eastern hardwood forests. Information about chestnut restoration
activities in Pennsylvania is available on the Pennsylvania
Chapter of TACF's Web site.
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Source: Pennsylvania
Chestnut Tree Blight Commission
In this photo taken early
this century, a portable sawmill is used to process blighted
trees. Until a fungus was introduced in America, the American
chestnut, highly valued for its lumber and the food it
provided both humans and wildlife, was the most abundant
tree species in Pennsylvania.
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For information about volunteer activities, please contact the
following:
Sara Fitzsimmons
Research Support Technologist
The Pennsylvania State University
School of Forest Resources
206 Forest Resources Laboratory
University Park, PA 16802
814-863-7192
sff3@psu.edu
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Sara Fitzsimmons, tree breeding program coordinator, assisting with
the inoculations.
