Industry rebuilding | Fewer than 2,000 chestnut trees remain in Ontario
ST. THOMAS, Ont. — The American chestnut, once a dominant species throughout Appalachia and as far north as southwestern Ontario, is making a comeback.
It’s a recovery that’s been measured in years and decades, but that may changing, thanks to a grafting technique developed by a University of Guelph researcher.
Dragan Galic has learned how to sprout nuts and then attach twigs from trees with known resistance to the chestnut blight, which has all but wiped out the American chestnut from North America.
New wood from the cloned trees can be harvested the following year and grown through to vegetative propagation.
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“This could help us to propagate resistant chestnuts for commercial purposes quickly,” Galic said.
Trees grown using the technique also produce pollen in a year or two instead of the five or six that’s normally required.
A breeding program has been in place in the United States for decades, but it wasn’t until the 1980s that substantive progress was made.
U.S. breeders had previously crossed the American chestnut species, canstanea dentate, with its Japanese, Chinese and European cousins, but the percentage of imported genetics was high. They used a backcrossing process to reduce the overseas component and at the same time managed to bring resistance forward.
Galic continues this work, backcrossing to resistant trees found in Ontario. He also maintains a pure line of Ontario genetics from 26 “mother trees” that have survived the disease.
“We couldn’t find any statistical difference in the level of resistance between our native stock and the American stock,” Galic said.
Resistance has three main forms:
- bark, which provides a barrier to disease entry
- the ability of trees to cover wounds with callusing
- production of phytoalexins, plant-derived antibiotics, that attack the blight
The breeding program crosses the most resistant trees, which are the ones that develop the smallest lesions when exposed to the disease.
It’s hoped the level of resistance can be incrementally increased through successive generations to the point that American chestnut populations can be reestablished throughout their former Ontario range, said Adam Gale, a professor emeritus at the university’s Simcoe Research Station, who is working with Galic.
That could begin in a small way in as little as five years, added Galic.
“These are fast growing trees. I’d like them to be able to live at least 50 years (before succumbing to the disease),” he said.
“We already have about 30 people on a list who are interested.”
Gale said nature will take over once the trees are established in the wild. Those trees with greatest resistance will be favoured as the years, decades and centuries pass, handing down their resistance to their offspring.
Tree structure, nut size and other aspects of the American chestnut are also being considered.
The species was widely harvested for high quality lumber before the arrival of the chestnut blight in the early 1900s.
It also served as a food source for people and wildlife.
The forest giant may have comprised as much as 40 percent of the canopy in southwestern Ontario.
Today, there may be as few as 1,000 to 2,000 of these trees left in the province.
