Grafting toolsThe Chattanooga Chestnut Tree Project Annual Report for 1999

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The goal of the Chattanooga  Chestnut Tree Project is the restoration of the American chestnut to the Southern Appalachian and Cumberland Plateau Regions.  The return of the chestnut to its place in the forest canopy requires a two-part plan of action: research on biological control of the chestnut blight disease and breeding the trees for disease resistance.  A secondary goal of the Project is to provide support for the establishment of a commercial chestnut industry (for nut production) based on improved cultivars.

The Chestnut in Chattanooga.  The Chattanooga community has a long history of involvement with  the chestnut tree - historically - and most recently with restoration of the American chestnut tree.  Primarily due to the effort and enthusiasm of one man, the late William G. Raoul of Lookout Mountain, Tennessee, the Chattanooga Chestnut Tree Project is now supported in part by the Summerfield Johnston Endowment for the Restoration of the American Chestnut and the Robert M. Davenport Professorship of Biology at the University of Tennessee at Chattanooga.
        Field work is ongoing at four locations; Bendabout Farm, The Lula Lake Land Trust, The Tennessee River Gorge Trust and Reflection Riding Arboretum.

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Scope and Accomplishments to Date.  The long-term goal of the project is the restoration of the American chestnut, Castanea dentata, to its former position as a component of the southern Appalachian hardwood forest ecosystem.  A secondary goal is to provide support for the establishment of a commercial chestnut industry (for nut production) based on improved cultivars.  The restoration effort relies on a two-part approach to solving the problem of chestnut blight:  Breeding for blight resistance and biological control of the chestnut blight fungus.  The breeding work, in turn, will depend on the continued availability of locally adapted American chestnut trees (southern germplasm) to use as parents.  My role in the Project will be to establish University research objectives designed to accomplish the long-term goals. Research is planned or currently underway in all of the following project areas:
 

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Bendabout Farm.  Bendabout farm is a privately owned property located about 40 miles east of Chattanooga in the Ridge and Valley domain, near Cleveland, Tennessee.  The owners have been very supportive of the chestnut project and quite willing to enter into Memoranda of Agreement with UTC and TACF for long term cooperation. The chestnut plantation there now includes four separate orchards.  The first, Orchard #1, was planted between November 1992 and March 1993. It is composed primarily of Castanea  dentata   (30 transplants) collected as saplings from a wild population found in Attala County, Mississippi.  This central Mississippi population of American chestnut marks the extreme southwestern boundary of the native range for the species and may be  very interesting from a genetic perspective.  Fifteen other trees in the first orchard were transplanted from Lookout Mountain, Georgia and two trees were found locally at Bendabout Farm.  Orchard #1 also includes one grafted tree of a clone from Lookout Mountain.
        Orchard #2 includes about 120 trees that were grown from seeds planted at the site in May 1996 and March 1997.  The seed nuts planted were the fruit of open pollination of second backcross (B2) trees at TACF Research Farm, Meadowview, Virginia.  The resulting seedlings are designated B2F2s. The B2F2 planting will be measured for growth, form blight resistance and other segregating traits according to TACF guidelines. Orchards 1 and 2 are fenced and gated.  Drip irrigation was installed and has been used effectively during summer drought.  Orchard #2 also includes six native chinquapins (Castanea  pumila).
        Orchard #3 is a planting of our own seedling progeny from crosses made at Bendabout Farm.  And orchard #4 is a small planting of 9 Japanese chestnut seedlings, Castanea crenata (from Connecticut).
        Results of the backcross breeding work at Bendabout include 17 hybrid trees from the 1996 season, 40 progeny from the 1997 season and more than 200 hand-pollinated seedlings from the 1998 season (Harvest Photo).  The 1999 pollination season went very well and fruit set appears very good (as of this writing, July 1999). Pollen from TACF-Meadowview was used all four years.  In 1998 and again in 1999, I also employed pollen collected locally from two large Chinese chestnuts (FF-2-1 and FF-5-1), part of large planting of introduced chestnuts made in the 1930s by the Tennessee Valley Authority.

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Reflection Riding Arboretum and Botanical Garden.   The existing chestnut species collection at the Arboretum includes mature specimens of Chinese chestnut (C. mollissima), native C. dentata sprouts, some recently planted seedlings of C. dentata  from Lula Lake, Japanese chestnut (C. crenata)  and chinquapin (C. pumila).  The Arboretum seems almost ideally suited for building a good germplasm collection (chestnuts grow well there) and progeny testing (particularly for gall wasp resistance).

Bill Chipley at Lula LakeLula Lake Land Trust.  The private, non-profit Trust manages and protects several thousand acres of land in the Rock Creek watershed on Lookout Mountain, in Georgia about 10 miles south of Chattanooga.  The Lula Lake population of surviving American chestnuts represents a very important genetic resource and will be the source of much of the germplasm used in the Chattanooga breeding program.  Surviving American chestnut clones are being mapped and labeled with metal tags.  The term "clone" is used because most of the surviving specimens appear as clumps of multiple stems arising from a common root, although the connections are not always clearly evident.  Several of the larger stems appear physiologically mature (they may bloom) and will be watched with particular attention during the growing season.  These trees have survived probably because they have escaped blight infection to date, not because they are resistant to the fungus.  The largest stems are all heavily cankered with blight and many stems are dead.  The chestnut blight fungus (Cryphonectria  parasitica) was isolated from bark cankers on three separate clones and is being grown in pure culture in the laboratory.  The Lula Lake C. parasitica  isolates have been converted to hypovirulent and will provide the basis for eventual biocontrol efforts (see "Biological Control" below).
        Two "orchards" were established in 1998 at Lula Lake.  One is a "B2F2" seedling orchard planted using seed from Meadowview.  200 open pollinated seeds in three families were planted into an open forest setting.  The canopy is a mix of oaks and pine.  The other orchard is of 100 C. dentata  seedlings from The American Chestnut Cooperators Foundation .  For more about the Chestnut Project at Lula Lake, follow this link.

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Tennessee River Gorge Trust. A demonstration plot was established at the southern tip of Williams Island.  Although the purpose of the planting is primarily educational,  this planting will allow a direct comparison of growth habit, form, chestnut blight resistance and climatic adaptability for all of the different chestnut species.  So far, four species are included:  American chestnut (Castanea  dentata), Chinese chestnut (C.  mollissima), Japanese chestnut (C. crenata), and Allegheny chinquapin (C. pumila var. pumila).  Five seedlings of each species were planted on May 14 by UTC students.  Wire cages were installed over the small trees for protection from deer-browse.  Hybrids and other species will be added to the Williams Island planting in the future.

    Campus Chestnut Nursery and Propagation Facility.  Progress is being made on the development of a chestnut nursery/propagation facility to be located on the UTC campus.  I have a small greenhouse and a partly shaded container yard.  All of the trees (seedlings and grafted trees) are grown in containers.

    Germplasm Collection.  Chestnut Project germplasm is listed in Table 1.  Additional germplasm collections will be made from throughout the Southern Appalachian and Cumberland Plateau regions. The breeding orchard will be a diverse population of southern C. dentata  types.  This will allow us to choose an American parent for each new breeding line that is well adapted to the local growing conditions and will increase the likelihood that our future hybrids will grow well here.  Rather than transplant from the wild, new additions to the breeding orchard will be made as grafts onto seedling rootstocks.  Advantages to this approach include the possibility of earlier bloom for breeding, genotypic evaluations of the selections and lastly, from a conservation perspective, the parent clone will not be removed from its place in the wild.  For example, scionwood (small twigs with dormant buds) were collected in late winter from the labeled clones at Lula Lake, within the Tennessee River Gorge Trust and from several other sites on Lookout Mountain and Walden Ridge.  The scionwood was grafted onto rootstocks growing in the propagation greenhouse and then transplanted to the breeding orchard.  In this way, the surviving Lula Lake trees will be multiplied without risking loss of the parent clone.
        Exotic germplasm will be added to the breeding orchards in order to maximize the diversity of our resistant parents.  The search for additional sources of blight resistance will include other species of chestnut not well represented in the TACF breeding program as well as diverse cultivars of European, Japanese and Chinese chestnut different than the parents used in the original TACF crosses.  Recent germplasm acquisitions are listed in Table 2.

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Table 1.  Type and number of chestnut trees at Chattanooga1, July 1999, with the number of sources of blight resistance and the number of American chestnut lines.





                                                                                                Number of
                                                                                  Sources of            American
Type of tree                                            Trees           Resistance              Lines
American (Mississippi)                            30                                               30
American (Northwest Georgia)                15                                               15
American (Southeast Tennessee)                2                                                 2
American (Western Virginia)                  100                                                  ?
Chinese2                                                 >50                       ?
Japanese                                                 >10                       ?
Chinkapin                                               >10
American hybrids (B2F1)3                       38                      3                        3
American hybrids (B2F2)                     ~250                      3                        8
American hybrids (B3F1)                       ~60                      1                        1
Other hybrids4                                        ~20                      1                        1


1  Includes breeding and germplasm orchards at Bendabout Farm, Lula Lake Land Trust, Williams Island and Reflection Riding Arboretum.  Does not include native C. dentata sprout populations.  Does not include recent accessions currently in propagation.
Includes established, mature trees (30-60 years old) at Reflection Riding and on TVA property at Ware Branch (Friendship Forest).
3  Progeny of Bendabout Farm crosses
Male sterility study
 

Table 2.  Recent Germplasm acquisitions at Chattanooga.





                                                                                            Number of
                                                                                Sources of              American
Type of tree                                        Trees           Resistance                  Lines
American (grafted clones)                     5                                                   5
Chinese (rootstocks)                         ~100              ?
Japanese                                             ~50               ?
Chinkapin                                           ~20
American x Chinese hybrids (F1)        15              2*                                 3
American hybrids (B2F1)                    66              3                                   3
Other hybrids and seedlings **         ~200             1                                   1


* Sources of resistance are: FF-5-1 and FF-2-1 from the "Friendship Forest" TVA planting at Ware Branch.
** Includes seed introductions from Europe, Australia and collaborative work with the Connecticut Agricultural Experiment Station.

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    A new threat to the American chestnut.  The oriental chestnut gall wasp Dryocosmus kuriphilus, is a tiny insect that lays its eggs in the buds of susceptible chestnut trees.  The infestation causes a gall to form instead of a normal shoot, quickly affecting the productivity of the tree.  Severely infested trees may weaken and eventually die.  This pest is native to northern China and was first seen in this country in the 1970s after its accidental introduction to the State of Georgia.  The gall wasp is credited with the near total collapse of the chestnut orchard industry in Georgia in the early 1980s.  It is now moving northward throughout the native range of Castanea  dentata.  Chestnut species that possess resistance to gall wasp may include C. crenata, C. mollissima, and C. pumila.  Inclusion of these species in the American chestnut breeding orchard will permit breeding for resistance to this serious pest.

   Student Projects.  One goal of the Chestnut Project as it was originally envisioned by William Raoul and the Late Provost Dr. Grayson Walker of UTC was that it should involve university students at every level.  There are several student projects currently underway.
        Survey of surviving Castanea dentata germplasm in the South Cumberland.  The students are helping me on a census and mapping of Castanea  dentata germplasm in the Chattanooga area.  Specifically we proposed to survey the Tennessee River Gorge, Lula Lake Land Trust and similar adjacent  areas for surviving American chestnut stems.  We use a systematic survey technique with the intent to map the location and densities of the living sprouts.  Scionwood was collected for grafting into the breeding orchard now being established at UTC.  Ideally we will be able to collect and identify a significant sample of southern C. dentata  germplasm from the Cumberland Plateau.  The survey will permit a detailed study of the chestnut blight fungus, Cryphonectria  parasitica , for future inoculation with hypovirulent strains.
Biological control of chestnut blight.   The students are working with me on the chestnut blight disease problem.  Our hope is to apply some biological control methods to the fungus Cryphonectria  parasitica.   Biological control is based on "hypovirulence," a phenomenon marked by the reduced virulence of the pathogenic fungus, making it less dangerous for its host.  Hypovirulence is transmitted by a virus.  The viral RNA can transform "lethal" cankers into slower growing superficial bark cankers that do not kill the tree.  Slowing the growth of the fungus allows the tree to live and bear fruit. We isolated the fungus from the native chestnut trees in the Tennessee River Gorge, Lula Lake Land Trust and from Bendabout Farm Orchard #1 .  The  isolates in pure culture were paired in compatibility group tests and converted to hypovirulent by Dr. Sandra Anagnostakis, Connecticut Agricultural Experiment Station (CAES). We are using two viruses - one from France and the other from Italy.  Three hypovirulent strains were deployed in orchard #1 at Bendabout Farm.  Different from the normal, lethal strains of blight fungus, the virus-containing hypovirulent strains cause a swollen, superficial canker with healthy bark tissue underneath.   The first inoculations at Bendabout were done in early June 1998.  At monthly intervals, we inspect all of the treated cankers, reinoculate some cankers and treat newly-formed cankers.  We have seen some evidence that this biological control may be working; some of the treated cankers have ridges of callus tissue forming along the canker margins - a sign that the chestnut blight fungus was attenuated.

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Related Publications of Project Members

Craddock, J.H.  (1999)  Chestnut Resources in North America.  Annual Report of the Northern Nut Growers Association 89: in press.    Click here for the web version of this paper.

Bassi, G. and Craddock, J.H.  (1998)  Performance and description of the introduced chestnut cultivar 'Colossal' in Cuneo province, northwest Italy.  In: Salesses, G. (ed.) Proc. 2nd International Chestnut Symposium, Bordeaux, France.  Acta Horticulturae 494: 317-318

Craddock, J.H. and Bassi, G.  (1998)  Effect of clonally propagated interspecific hybrid chestnut rootstocks on short-term graft incompatibility with four cultivars of Italian "Marrone". In: Salesses, G. (ed.) Proc. 2nd International Chestnut Symposium, Bordeaux, France.  Acta Horticulturae 494: 207-121  Click here for the web version of this paper.

Craddock, J.H. and Bassi, G.  (1998)  Introduction into Italy of eight  Castanea mollissima cultivars from China.  In: Salesses, G. (ed.) Proc. 2nd International Chestnut Symposium, Bordeaux, France.  Acta Horticulturae 494: 319-321

Craddock, J.H.  (1997)  Castanea genetic resources in North America.  Keynote speech (invited).  COST G-4 Multidisciplinary Chestnut Research Workshop on Tree Physiology and Genetic Resources of Chestnut.  Torre Pellice, (Torino) Italy, 18-21 June 1997.  European Commission and Universitą di Torino Dipartimento di Colture Arboree (in prep.).

Craddock, J.H.  (1998)  The Chattanooga Report.  Report to the US Dept. Agriculture NE-140 Regional Project on Biological Improvement of Chestnut.  College Park, Maryland.  10-12 September 1998.

Craddock, J.H.  and Schlarbaum, S.E. (1997)  The Tennessee Report.  Report to the US Dept. Agriculture NE-140 Regional Project on Biological Improvement of Chestnut.  Matamoros, PA.  19-21 September 1997.

Craddock, J.H. (1996) The Chestnut in Italy.  Proc. Nut Growers Soc. OR, WA & B.C.  81:69-78.


For more information about chestnut, try clicking on the links below:

The American Chestnut Foundation


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