Chestnut blight fungus is a disease caused by the pathogen Cryphonectaria parasitica, which primarily affects American chestnut trees. This fungus was introduced to North America in the early 1900s and quickly spread, leading to the near extinction of these trees. The fungus attacks the bark, causing cankers that disrupt the tree's ability to transport nutrients and water. The impact of chestnut blight has been significant, as the American chestnut was once a dominant tree species in eastern forests. Efforts to combat the blight include breeding resistant tree varieties and exploring biological control methods to restore the chestnut population.