 Efforts started in the 1930s are still ongoing to repopulate the country with these trees, in Massachusetts and many places elsewhere in the United States.In the 1970s, geneticist Charles Burnham began back-breeding Asian chestnut into American chestnut populations to confer blight resistance with the minimum difference in genes.In the 1950s, the Dunstan chestnut was developed in Greensboro, N.C., and constitutes the majority of blight-free chestnuts produced in the United States annually.