If "American Chestnut, part 1," you learned that the American Chestnut tree was a towering and grand component of our eastern forests and that its lumber and nuts were highly prized. You also learned that in 1904 a deadly fungus (Cryphonectria or Endothis parasitica) arrived in the U.S. and quickly wiped it out.
Recently some excellent progress has been made in combating that disease and I, for one, am keeping my fingers crossed in hoping for its recovery. A few years ago, scientists in France discovered that a related fungus damaged Chestnut trees but did not kill them. Sandra Anagnostakis of the Connecticut Agricultural Experiment Station began treating the wounds in American Chestnut trees with this new fungus. While this innoculation did not cure the disease and also caused deep gnarly wounds, this "biocontrol" approach importantly kept the trees alive long enough for them to flower and reproduce.
Meanwhile other scientists learned that the Asian Chestnut trees have at least two genes that allow them to successfully resist the lethal fungus. These trees, however, are smaller than the American variety and can't compete for the all-necessary sunlight in our forest canopy. However, researchers like Anagnostakis saw an opportunity and they began a cross-breeding program combining the Asian Chestnut with its American counterpart.
At the Connecticut station, Sandra's crossbreeding program required her to wait for the American Chestnut trees to bloom. She then covered the flowers with a paper bag to isolate them from pollen. When the flowers were fertile, she removed the bags and the desired Asian tree pollen was "simply dumped" on them. Then the bags were replaced. In the fall the bags were cut off and the nuts gathered and stored over the winter. After germination in the spring, the nuts were planted.
By continuously crossbreeding she has produced trees that are 15/16 American and plans to continue the process until the only Asian component is the desired genes to protect the tree from the fungus. Sandra believes that "chestnut trees should once again tower above the forest canopy." Let's hope so!