Summer 2024 7 In 1904, a small inquiry about American chestnut health at the New York City Zoological Garden indicated the start of a devastating blow to forests of the eastern United States. A parasitic fungus, now known as “Chestnut Blight” (Cryphonectria parasitica), had arrived on our shores. The blight originated in Asia where it naturally occurs within Chinese and Japanese chestnut trees, although these Asiatic trees exhibit co-evolved resistance. Over the course of 50 years, this blight spread across the native range of American chestnuts with devastating effects resulting in an estimated loss of four billion trees. This blight reduced our towering chestnut trees, which often reached more than four feet in diameter, to shrubby stump sprouts that could only survive for about five years before resprouting or succumbing to blight. The loss of this foundational forest species also meant the loss of the rot-resistant timber it provided (a quarter of all hardwood timber cut for lumber in the Southern Appalachians) and the nut crop that many people and wildlife relied upon. As the chestnut disappeared from our canopies, it was replaced with oak and hickory as dominant species. While both are hard mast producing trees, they were not able to completely fill the ecological and economic role that the abundant chestnuts once held. The American chestnut persists in our forests as small stump sprouts that survive in the shaded understory for multiple years but now rarely reach an age to produce burs. Due to the rarity of this tree, stumbling across a chestnut sprout is a fond experience for hikers and tree-enthusiasts. The Virginia Department of Forestry (DOF) enters the story of the American chestnut in 1967 with conversations between the agency’s State Forester George Dean, University of Virginia professor and corn geneticist Dr. Ralph Singleton, Dr. Dick Jaynes of the Connecticut Agricultural Experiment Station, and the philanthropist Anne Valk. Two years later, Valk would gift 422 acres of land to the Commonwealth of Virginia through the Lesesne Foundation (named for her father, Archibald Marion Lesesne du Pont) specifically for chestnut research and restoration. This newly acquired land would soon become one of the largest experimental planting of chestnuts since the blight began. One of DOF’s smaller state forests, Lesesne is located at the base of the Three Ridges Mountain. It was originally used as farmland until 1946 when it was first converted to apple orchards and then eventually to chestnut orchards in 1969. Meanwhile, in other parts of the eastern U.S., the straightest and tallest Chinese and Japanese chestnuts were being crossed with the American chestnut by scientists with the aim to breed a blight resistant hybrid. By 1976, under the direction of the DOF Chief of Applied Research Blight canker on a hybrid chestnut at Lesesne State Forest (2024). Tom Dierauf, approximately 11,500 hybrid seedlings and 3,000 irradiated seedlings had been planted at Lesesne. The hybrid chestnuts included seeds and seedlings from the Connecticut Experimental Station that were open pollinated from the best hybrids in the country. Some controlled crosses from the Clapper chestnut and other selectively bred hybrids were also included in this first large-scale planting. The American chestnuts included in the original plantings had been irradiated by Dr. Ralph Singleton, now also the director of The National Colonial Farm, and Albert Dietz from Ohio. These chestnuts were exposed to irradiation in hopes of eliciting a mutation that caused blight resistance. This methodology had previously been used on farm crops with some success. Lastly, about 500 one-year-old seedlings grown at DOF’s Augusta Nursery from irradiated chestnuts were planted in 1976 at Whitney State Forest. Unfortunately, those trees all died due to blight. The goal for all these plantings was simple: observe the chestnuts as they grow to assess their blight resistance and American traits, and eventually choose the best specimens to cross and create further generations of resistant trees. When evaluating chestnuts for conservation and restoration, there are a few important factors to consider. The first is blight resistance, including both survivability and tree growth with the presence of blight. The second is “American-ness” of the hybrid. The Japanese and Chinese chestnuts have smaller, shrubbier forms which don’t fit the role of American chestnut as a dominant canopy and timber species in our native forests. Thus, one of our main priorities in a hybrid is to maintain the fast growth rate, straightness and single-leader qualities of the American chestnut while incorporating the vital blight resistance from its Asian relatives. Over the last 60 years, DOF has continued our breeding program by choosing the best hybrids and backcrossing them with American chestnut trees or other best hybrids from our orchards. We partner with multiple agencies and academic institutions, primarily The American Chestnut
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