Identification of American Chestnut Trees

Dr. Sandra L. Anagnostakis Department of Plant Pathology and Ecology The Connecticut Agricultural Experiment Station 123 Huntington Street, P. O. Box 1106 New Haven, CT 06504 Phone: (203) 974-8498 Fax: (203) 974-8502 Founded in 1875 Email: [email protected] Putting science to work for society Website: www.ct.gov/caes CHESTNUT RESTORATION FOR CONNECTICUT Chestnuts in Connecticut’s Early Forests chestnuts that were first imported in 1876. Connecticut was heavily forested in 1600, Japanese chestnut trees were also available but by the early 1800’s, forest covered only from catalogs, so mail-order movement of about 20% of the state. Now trees have infected trees helped to spread the fungus. grown up on land no longer farmed, and we Insects and small animals that walk over the are back to about 60% tree cover. In 1910, cankers also helped to spread the disease (5, when chestnut blight disease started killing 6). Chestnut blight disease reduced the our chestnut trees, half of the standing American chestnuts to understory shrubs, timber was chestnut and there were about which die, sprout from the base, die, and 130 million mature American chestnut trees sprout again. The fungus is now present in the state. Chestnut was the only wood throughout the original range of C. dentata, used for telephone poles and most of the and has spread to many areas of the Midwest railroad ties were chestnut. The trees were where chestnuts were planted. tall and straight, and after clear-cutting, they easily out-competed the other hardwoods to The Experiment Station and Chestnuts dominate the forests, making pure stands. The first plant pathologist at The Connecticut Agricultural Experiment Station American chestnut, Castanea dentata, is (CAES), George Clinton, studied the native from southern Maine to northern progress of chestnut blight disease through Georgia, all along the Appalachian mountain our native chestnuts. The pathogen was range. In the early 1800’s, trees in the described, and the species was eventually southern coastal part of this range were named Endothia parasitica by another killed by ink disease. This disease is caused CAES scientist, Paul J. Anderson. by Phytophthora cinnamomi, and is still present in that region (6). Fortunately, this Chestnut Breeding in Connecticut organism cannot overwinter in Connecticut, Chestnut breeding work began early in the and so is rarely a problem here. However, U.S., but the only program that has chestnuts in Connecticut and other areas continued without interruption is the continue to be challenged by another program at CAES. In 1930, Arthur Graves disease, chestnut blight disease. The made his first crosses of American and chestnut blight fungus, now called Japanese chestnut, and began a long Cryphonectria parasitica (Murr.) Barr, collaboration with CAES geneticist Donald entered the U.S. on infected Japanese Jones. Graves gave CAES about 9 acres of his land in Hamden, CT with plantings of make them fully resistant to the chestnut species and hybrids, to insure the blight fungus (8). In order to control continuation of Connecticut’s chestnut pollination, female flowers are bagged in breeding program. Graves’ students Hans late June to protect them from pollen; Nienstaedt and Richard Jaynes of Yale selected pollen is subsequently put on the University, made many of the hybrids that flowers in July and the bags are closed. are still part of the current breeding Many hybrids are male sterile—catkins program. form, but the flowers never bloom to produce pollen. This is only seen in My early work at CAES included studies of interspecific hybrid trees, but is a feature the basic genetics of the blight fungus (and valued by nut growers who want to plant the system of vegetative compatibility that orchards of male sterile trees with a few restricts hyphal fusion and the transfer of pollen-producing trees for yields of nuts that biocontrol viruses from one strain to are uniform. another) and tests of extracellular enzymes produced by the fungus (1, 2, 14). CAES has what is probably the finest collection of species and hybrids of chestnut Our breeding plan was first based simply on in the world for use in this breeding making hybrids of blight-resistant Asian program; seven Castanea species are trees with susceptible American trees and represented. The breeding program will be testing the hybrids for resistance to chestnut greatly helped by studies using molecular blight disease (4). When it became clear genetics, which are currently underway (12). that at least two genes were responsible for Trees of two kinds are being chosen: for this resistance, we began a back-cross timber (tall and straight, with little energy breeding program based on the plan of put into forming nuts) and for orchard or nut Charles Burnham (8). Asian trees are production (short and spreading with crossed with American trees, and the maximum energy put into forming large, hybrids (partially blight-resistant) are good-tasting nuts). Both kinds of trees must crossed to American trees again. If there are have resistance to chestnut blight disease two resistance genes, one out of four of the and be well-adapted to our climate. We are progeny from these back-crosses have one also starting to select our trees for resistance copy of both resistance genes, giving them to ink disease, caused by the root pathogen partial resistance. If there are three genes P. cinnamomi. for resistance, one out of eight of the progeny will have one copy of all three Biological Control of Chestnut Blight resistance genes. Trees with partial blight Disease resistance are crossed again to American In the late 1950’s, a chestnut recovery trees. Repeated back-crossing increases the phenomenon was discovered and studied by percentage of American genes in the Jean Grente in France. He called the system hybrids, and selecting for partial resistance “hypovirulence,” because the chestnut blight insures passage of the resistance genes. A fungus that he isolated had less than normal final cross of two trees with partial ability to kill chestnut trees, and the “fungal resistance should result in one of sixteen sickness” could spread. We found that this trees having two copies of two resistance is due to a viral infection of C. parasitica (6, genes (or one of sixty-four trees having two 7, 9, 10) that is transferred from strain to copies of three resistance genes), which will strain when the hyphae fuse. The genes of Chestnut Restoration for Connecticut S. L. Anagnostakis 2 The Connecticut Agricultural Experiment Station (www.ct.gov/caes) three kinds of these (dsRNA) viruses have Griswold at the CAES Griswold Research now been sequenced, and the viruses placed Center, formerly the Connecticut State in the genus Hypovirus by Bradley Hillman Nursery. These will serve as our “seed and his collaborators (11). In Connecticut, orchard” for producing timber chestnut trees hypovirulence can keep trees alive in the for the forests of Connecticut. The rest will forest and orchards, and we have studied the be planted in state and private forests many kinds of organisms (e.g., birds, throughout the Northeast. squirrels, ants, and beetles) that move both killing and curing strains of the fungus from Ozark chinquapin tree to tree (3, 6). There has not been a Ozark chinquapins (Castanea ozarkensis) general recovery of forest chestnuts in are timber trees found on the Ozark Plateau Connecticut, but 10 to 15% of American in Oklahoma and Arkansas. They have a trees are kept alive and flowering. single nut in each bur, as do the Allegheny chinquapins (C. pumila) and Chinese Synthesis of Breeding and Biological chinquapins (C. henryi). Chestnut blight Control disease has recently reached their native American chestnuts range on the Ozark Plateau, and this disease, Chestnut seeds of four kinds of hybrids were in combination with forest fire damage and planted in Griswold at the Connecticut State land disturbance, seriously threaten their Nursery in the spring of 1998. The resulting survival. We have started testing Ozark 500 chestnut trees were lifted in the spring chinquapins for resistance to chestnut blight. of 2000 and 100 of them were planted in a We have 65 of these from Oklahoma and clear-cut in Prospect on land owned by the Arkansas ranging in age from 6 years old to Town of Prospect and managed by the 73 years old. In addition, we have many Connecticut Water Company, and 25 were hybrids of C. ozarkensis crossed with planted in a clear-cut at Sessions Woods various Asian chestnuts and ranging in age Wildlife Area in Burlington. These trees are from 5 years old to 50 years old. Since being evaluated for survival under forest these hybrids have already been evaluated competition conditions. Of the remaining for form, similarity to C. ozarkensis, and seedlings, the 200 best were planted in an resistance to chestnut blight, they will be orchard at the CAES laboratory and farm in useful in a back-cross breeding program to Windsor. The Windsor trees with the best improve the fitness of the chinquapins. We timber form, hardiness, and blight resistance have been crossing our Ozark chinquapins have been selected over the years since with each other and with Chinese planting, and the rest have been removed. chinquapins, Japanese chestnuts, and There were 50 trees left in 2006 and their hybrids, and these will be back-crossed to C. offspring were planted in 2007 in the ozarkensis. Using all of these methods we Goodwin State Forest, in the Farmington expect to produce trees that will have a Town Forest, at Windsor, and on private better chance of surviving in their native land in Connecticut and New York. In the habitat. fall of 2007, we sent 2,500 nuts from the best of the Windsor trees to Georgia to be The Next Problem raised for us in a commercial nursery.

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