The future of the chestnut tree

The future of the chestnut tree

There have been many scourges to strike this planet from the Bubonic Plague to the AIDS epidemic but humans are not the only living things that have been affected. A fungal blight wiped out nearly every chestnut tree in North America in the early 20th century and it has prevented re-population of the species even to this day. In an attempt to find a cure for this blight another species of chestnut tree was used to find a cure.

The Asian chestnut tree was found to be resistant to the fungal blight. Attempts to introduce these trees to combat the blight began in the 1920s but were not successful. The Asian chestnuts simply were not able to compete in North America’s forests and were not able to thrive and the program was abandoned by the 1960s.

The blight is a fungal infection spread by spores in the wind. The infection forms a canker sore beneath the bark killing the cambium all the way around the circumference of the tree. A toxin is produced and introduces an acid that lowers the pH of the infected cells to toxic levels killing everything above the infection. Chinese and Japanese chestnut trees were found to be much more resistant to the blight than their North American cousins but were not immune. They had developed a resistance before the fungal blight broke out here and it was when these trees were introduced into North America that the blight spread.

Other methods to fight the blight were tried and proved to be failures as well and by 1983 scientists had come full circle. Another cross-breeding program was initiated. These hybrid chestnut trees would be mostly American chestnut to keep the timber and only the genes responsible for blight resistance would be introduced. This was the brainchild of Dr. Charles Burnham who helped found The American Chestnut Foundation. He realized that the earlier program had made one major mistake, resistance to the blight was never bred into new trees.

This is a complicated process. Four successive crosses of the two chestnut species were believed to be needed in order for the genes that resist the blight to become heterozygous. A further subset of these trees will have a dominant Asian gene which can then be used for breeding. With the sixth generation of breeding completed and after 25 years it was time to put Burnham’s idea to work.

On U.S. Forest land in 2012 in Virginia, North Carolina and Tennessee several hundred little chestnut trees were planted. After one growing season the trees all stand between three and seven feet tall and are maturing faster than expected. These trees, known as Restoration chestnuts, are beginning to produce nuts as well, over 13,000 of them. In 2013 500 new Restoration chestnut trees were planted on private land in western Pennsylvania to give a real world test in a place appropriately named Chestnut Ridge.

Others are working on this project as well from other angles. Another group at the SUNY College of Environmental Science and Forestry found that by introducing a wheat gene an enzyme would be released that would detoxify the fungus. Their method requires no interbreeding with the Asian chestnut and is awaiting approval from the federal government. Only two genes out of 40,000 were altered, much fewer than the 2,500 genes that are switched by backcrossing. They believe that blight resistance on the early specimens are picked up in the laboratory and will pass those genes onto their offspring.

This is exciting news. The chestnut tree, once one of the dominant trees of the United States may be on its way back. By all regards it seems as if these Restoration chestnuts are doing well but there is still a lot of work to do before the species returns to its former glory.

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