Chestnut Blight is a fungal disease caused by the pathogen Cryphonectaria parasitica, which affects American chestnut trees. This disease was first identified in the early 1900s and has led to the near extinction of these trees in North America. The fungus infects the bark, causing cankers that eventually girdle and kill the tree. The spread of Chestnut Blight was accelerated by the introduction of infected trees from Asia, where the Chinese chestnut has some resistance. Efforts to restore the American chestnut population include breeding programs and genetic engineering to develop blight-resistant trees.