Construction
Hybrid Chestnut
Seed Orchard

 

 

Source: Tim Phelps
"… A variety of chestnut can be created that is essentially American chestnut in all respects except for being resistant to blight."
 

 

 

 

 

The plantation should become larger and larger each year as more selected parent trees from the fourth generation reach maturity and begin intercrossing.

 

Source: Greg Grieco
Tim Phelps, research technologist for the hybrid chestnut plantation, explains the methodology of the breeding program during a field trip on April 30, 2003. Standing beside Tim is Kim Steiner, director of the Arboretum.

 

 

 

 

 

Source: Tim Phelps
Looking down a row of chestnut seedlings after a December snowfall.

 

 

 

Early in 2004, the Pennsylvania Chapter of The American Chestnut Foundation installed a protective fence around the expanding orchard.

 

 

 

 

 

 

Sara Fitzsimmons, tree breeding program coordinator, assisting with the inoculations.

 

 


Hybrid Chestnut Seed Orchard

 

Chestnut Research Milestone Achieved at Penn State's Arboretum
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.

History of the Orchard at Penn State 

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).

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.
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.

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.

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."

 

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 2003, 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.

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 is able to determine the level of resistance of the tree based on the tree's response to the wound. Initial selections of breeding stock are made in the fall, followed by final selections in spring.
 
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 are made when selected plants are flowering.

Rating Blight Resistance (November 2005)

By fall 2005, 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, a research technologist, 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.

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.

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.
 

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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