Early Efforts to Breed a Blight Resistant Tree
The blight (initially named Endothia parasitica and later changed to Cryphonectria parasitica) was first reported in 1904. Huge efforts were taken by state and federal governments to halt it spread, with Pennsylvania even cutting a several miles wide swath of forest to halt its spread westward. As it became clear that efforts to contain the spread were not working, efforts shifted to creating a blight resistant variant of the tree.In 1925 the US Deptartment of Agriculture began a program aimed at developing blight-resistant hybrids that would be able to compete in the forests. Several years later a program was developed at the Brooklyn Botanical Garden, and later transferred to the CT Agricultural Experiment Station (CAES). Both of these programs sought to establish blight resistance by breeding resistant Chinese chestnut (Castenea mollissima) or Japanses chestnut (Castenea crenata) with surviving and flowering American chestnuts.
By the late 1940s, several thousand hybrids had been developed, and Jesse Diller, formerly of the USDA, worked with others to plant the trees from Glenn Dale and CAES at forest plots along the original range, with the goal being the test of growth under forest conditions. A total of 1746 trees were planted at fifteen sites. These included 500 chinese chestnut hybrids and 541 hybrids from the promising tree PI-58602 both raised at Glenn Dale. There were an additional 705 hybrids from CAES. There were three sites located in Connecticut, two in Coventry, and one at Great Mountain Forest in Falls Village. These trees were measured and evaluated annually until 1978, and a summary report was written shortly thereafter by Frederick Berry of the US Forest Service. The conclusion was that none of these trees had developed into a blight-resistant forest stand – indeed it was never expected they would. It was noted that there was some success, and that trees showing promising levels of resistance, should be used for more extensive research and propagation.
Of interest was that one of the trees that Jesse Diller evaluated had been planted by Russell Clapper. Said Diller, “Russell B. Clapper has reported a promising new forest-type hybrid chestnut tree. This artificial hybrid forest tree is formerly named here as a new cultivated variety (cultivar), ‘Clap-per’ chestnut, in honor of its originator.” The background was (Castanea mollissima ♀ X dentata ♂) ♀ X dentata ♂, Backcross of a Chinese-American hybrid chestnut with the latter parent tree. And this was much later leveraged as the starting tree for resistance in the Connecticut TACF program.