We’ve probably all heard of the American chestnut, and its fatal succumbing to a fungal infection brought from East Asia.
This is about all I knew about the topic, aside from that many are sad about the loss of this tree, before hearing the Nature Connection Series presentation at the WVU Core Arboretum last week. Amy Metheny, a WVU research assistant in forest pathology and environmental microbiology gave an overview of restoration efforts for this tree.
According to the American Chestnut Foundation website, this tree was almost perfect. The north eastern United States forests were full of them — over a century ago there were nearly four billion trees dominating the woods in our area of the country.
The American Chestnut grows fast — up to 100 feet tall with a diameter often over 10 feet – straight and tall and bears tasty nuts. This made the tree optimal for timber for building homes, furniture and fences as it was also rot resistant. The nuts fed humans and a plethora of wild animals and livestock.
But when the chestnut blight was introduced to this region around the turn of the century (likely by import of a different species of chestnut tree from Asia), this once dominant tree became practically eliminated within about 40 years. This was after it had survived for over 40 million years.
The blight, fungus Cryphonectria parasitica, attacks the tree through any wound — anything from insect damage to a broken limb, and creates a bright orange canker. It then grows in and under the bark, eventually circling all the way around the tree.
As it grows it produces oxalic acid among other toxic compounds. The oxalic acid lowers the tree’s pH from around 5.5 to 2.8, which kills plant cells. The result is a dead tree from the fungal infection and up.
The roots however, don’t die and we still have American chestnuts growing in our forests – sadly mostly in the form of clumps of understory trees sprouting from root systems, before reinfection occurs.
Spores from the fungus are spread both by wind and mechanically mostly by birds but also by other animals as they come in contact with the infection on a tree, and then touch another tree.
The American Chestnut Foundation works on restoration of the majestic tree via breeding, biotechnology and biocontrol.
The breeding approach involves hybridizing the American chestnut with the Chinese chestnut over multiple generations to create a tree that is mostly American chestnut with just enough Chinese chestnut genetics to give it blight resistance. The Chinese tree is naturally resistant as it evolved alongside the parasitic fungus.
The biotechnology method involves inserting a gene found in wheat which produces an enzyme, oxalate oxidase. As I understand it, this neutralizes the oxalic acid so the tree can survive the infection.
The biocontrol prong was Amy Metheny’s expertise, and something which I would love to learn more about. Called hypovirulence, this involves infection of the fungus by a virus, weakening the fungus enough to allow the tree to use it’s natural defenses to heal the canker.
This last method of restoration sounds to me like the most elegant – helping nature just a little to regain balance.
Learning more about the American chestnut and the blight, piqued my interest. Since I heard the presentation last week I’ve been imagining what our forest must have looked like just a bit more than a century ago, filled with these incredible trees and all the smaller lives that thrived along with them.
