Many people believe that the American Chestnut is extinct. Technically, that’s never been true. Even the massive trees that fell victim to Chryphonectria parasitica sometimes resprout a hundred years later, before dying back to the roots. The American Chestnut Foundation, in fact, aims to restore the chestnut back to the eastern forests, albeit using a tree hybridized with the Chinese Chestnut:
The backcross method to introduce blight resistance from Chinese chestnut into American chestnut was first proposed by one of TACF’s founders, Dr. Charles Burnham, a renowned maize geneticist. Burnham’s rationale for backcrossing was based on the hypothesis that a few genes from Chinese chestnut are responsible for its blight resistance. Thus, it should be possible to dilute out most of the genes inherited from Chinese chestnut except for those involved in blight resistance and recover hybrids that are morphologically indistinguishable from American chestnut.
This has been accomplished through four successive crosses of a Chinese chestnut and its descendants to American chestnut (i.e., the F1, B1, B2, and B3). Each generation of backcrossing halves the proportion of the genome inherited from C. mollissima and the resulting third backcross (B3) hybrids are 15/16ths American chestnut in their genomic composition. The hybrid progeny of backcrosses to C. dentata inherit varying numbers of resistance genes from C. mollissima. In each generation the most blight-resistant individuals have been selected by artificially inoculating the hybrids with Cryphonectria parasitica (the fungus that causes chestnut blight) and culling out all trees except for those with with the smallest cankers. At the third backcross stage the small portion of the genome inherited from Chinese chestnut is expected to harbor genes or alleles that confer resistance to chestnut blight.
There are still unhybridized chestnut trees, though. I know, because I have two of them. I purchased mine as whippets from a great seed and plant coop, Fedco (I recommend them highly, BTW) from Maine. That was in 2003. The general rule of thumb is that trees growing more than 10 km from a fungus source will survive, and that a tree older than 10 years has successfully done so — though there’s never any guarantees. Mine are now 15, and in their 5th year of nut production. They are close enough to pollinate, and I have a handful of volunteer chestnut trees on my property. Unfortunately, squirrels love the nuts, and we are overrun with the cute, annoying rodents this year. Transplanting the trees also turns out to be a challenge, as the varmints can smell a transplant a mile away, and dig it up, looking for the nutcase (snipped off, but what do they know?). Still, my hope is that I can give away a few seedlings to friends who can outwit the squirrels and keep the chestnut going.
One of the few good things about climate change is that the chestnut blight has not spread beyond the tree’s original range. It’s possible, then, that unhybidized chestnuts could be successfully grown further north. In fact, I’m at the far north of the historical range, in New Hampshire.
If you want to help restore the American Chestnut, please consider giving to the American Chestnut Foundation. The Ballyshannon Fund of Charlottesville, Virginia is matching donations between now and the end of the year.