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Wednesday, August 13, 2014

A Second Chance for the Glorious American Chestnut

Snuggled into the woods in the western Massachusetts hilltown of Granville is an 18th-century homestead that I wish was waiting for me as I trudge out of the forest, weary and hungry at day's end. Hand-hewn timbers of a post-and-beam frame, wide chestnut floor boards, a fireplace with built-in bread oven; these are just a few of the heart-warming features of this fine old home.

John Meiklejohn amidst his chestnuts
But most inviting of all are the easy personalities of its lucky owners, John and Sarah Meiklejohn. And "Bodhi", the happy golden retriever, whose name derives from "bodhisattva", or "one who is on the path to enlightenment" (my first thought was, "why isn't its name 'Chestnut' ??"). They graciously welcomed three of us to their chestnut farm to see first-hand what restoring the American chestnut tree is all about.



On a typically hot and humid August morning, Bill Finn, Arnie Paye, and I visited John and Sarah, and John took us for a more than enjoyable walk through wood and field.


The Might of the Blight

As you may know, the chestnut was a major, towering component of the eastern American hardwood forest until an introduced fungus brought it to the ground. The disease was first discovered around 1900 in New York City; in less than 50 years, the blight had spread like western wildfire throughout the entire eastern forest system, and killed off virtually all of our billions of chestnut trees (a very few are hanging on). Or nearly killed them. Oddly, the fungus kills the above-ground portion of the tree, but leaves the root system unaffected. So today, you can wander the forests and commonly find chestnuts sprouting from dead stumps. Unfortunately, however, those sprouts will grow only perhaps a decade or two before they too are destroyed by the blight. That cycle repeats as long as the root system has the energy to send up more sprouts. (To read more about this, see this blog article.)
John, Bill Finn, Arnie Paye in John's seed orchard

TACF

On the happy side of all this is The American Chestnut Foundation (TACF), whose member volunteers (including the Meiklejohns) and scientists are working in lab and field to give our beloved chestnut a chance to rise again. Make no mistake, these people are dedicated. This restoration project has been and will be many decades in length. While the effort to save the chestnut began in the early twentieth century by others, it eventually was abandoned mid-century, as there was no success in sight. But in 1989, the effort was revived with the formation of TACF.

About six years ago, John was pondering what to plant on his land, thinking ahead to his retirement years. Maybe blueberries? He came upon an article about the efforts to restore the American chestnut to its former predominance, and as with a blacksmith's hammer blow, the idea was forged... it would be chestnuts. A patch of forest had to be cleared to expand a small field, and he was on his way.

Dot Your I's and Cross Your Trees

The strategy used by TACF is essentially "one step forward and three steps backward". Step one is to cross a blight resistant Chinese chestnut with an American chestnut; this is a "forward cross", yielding a half Chinese, half American hybrid. The idea is to get the genes that confer blight resistance on the Chinese trees into the American tree.

Male catkins on a BC3 chestnut tree
But the Chinese trees have other traits (such as a shorter, open-grown kind of stature, and lesser wood quality) that are not desirable in our American trees, which grew tall and straight in the forest. So the 50-50 hybrid trees are exposed to the blight; those few (likely fewer than one out of a hundred) that show the most promise of being resistant are then back-crossed with American trees. 

That first back-cross ("BC1") generation removes some of the unwanted Chinese genes (but hopefully not the resistance genes). Those BC1 trees are exposed to the blight, and again, the few that look promising are selected to be back-crossed again with American trees (yielding "BC2"). The process is repeated at least one more time to produce "BC3", the third back-cross, which will be about 15/16ths American chestnut, and 1/16th Chinese.

Burrs (nuts) on BC3 tree
Some small number of the many hundreds of trees so produced will hopefully retain the resistance genes, while also having almost entirely American chestnut genes. By far, though, most of the hybrids produced during this back-cross process fall prey to the blight after some number of years (which the growers are trained to expect, but I would find disheartening).


During this long process, each new generation must be allowed perhaps six or so years to grow to reproductive maturity so it can produce seeds (ie, chestnuts), which are planted to produce the next generation. In order to guarantee that the selected nuts actually are the offspring of the desired parent trees, the female flowers of the "mother" tree must be hand pollinated with pollen from the intended "father" tree, and physically covered with bags to prevent unwanted pollination from any other nearby tree.

John explains blight to Arnie









Blight canker on BC3 tree


















John explained to us that further steps are then taken: to ensure the trees have a diversity of American genes (as is found from region to region across the native range), the seeds of the BC3 generation are planted in "seed orchards".

John's seed orchard
In another six or so years, when these trees flower, they're allowed to be freely and openly pollinated by any nearby American chestnuts, to increase genetic diversity. No nearby Chinese chestnuts must be allowed to produce pollen at this point, since if they do, they will reintroduce the undesired Chinese genes (any such trees used for hybridization in the orchard are cut back or removed). Eventually, with enough seed orchards producing nuts, thousands of seeds will be available to restock the forests with American chestnuts.
Blighted chestnut hybrid

To promote the genetic diversity of the future chestnut population one would typically find in nature, growers in different areas of the country use various mother and father trees from diverse regions to create the next new generations. This will help the future trees cope with whatever stresses await them.
2-year-old seedlings from BC3 trees














 

 

 

 

 

 

 

Rich Hoffman's Project

In Wilbraham, Mass, there's another chestnut restoration afficionado, and TACF member, Rich Hoffman. Rich planted his trees in the spring of 2008 (so they are in their seventh growing season). They're in a lengthy row on the edge of a cornfield owned by a local long-time farmer who was gracious enough to let Rich use the strip of land. When I first visited him several years ago, his trees were about 5 feet tall. Most of the trees are first generation Chinese-American 50-50 hybrids ("F1" trees). Some are now up to about sixteen feet in height. Because of the Chinese genes, their growth habit tends to be multi-trunked and bushy, "like an apple tree", as Rich says. A forest-grown American chestnut tends to be a straight, tall, single trunk tree.
Rich Hoffman's row of chestnuts

One of Rich's goals is to develop blight resistant American trees that are derived from chestnuts (American and Chinese) located in western Massachusetts. He has learned a lot about growing chestnuts, and has had some of the same problems John has, such as meadow voles chewing the bark off trunks, and the need for weeding around the trees. And if you use pollen from a Chinese chestnut on an American (as Rich did), your hybrids will be male-sterile, ie, the male catkins grow, but don't form the little pollen-producing structures.This keeps the "F1" trees from inter-pollenating.

Sterile male catkin
His trees were also in the path of the nasty 2011 tornado that ripped a 39-mile swath across western Mass; some were lost, but thankfully not all.
Rich, with one of his all-American trees

An encouraging sight!


Bags protect burrs from unwanted pollen
In the spring of 2012, Rich planted eight pure American trees sourced from three American chestnut trees growing close enough together to inter-pollenate naturally. Those small fully-American trees will be old enough to provide him a ready source of pollen in a few more years, provided the blight does not cause them all to die back before male catkins appear.

While he hasn't purposely inoculated his hybrid trees with blight to test their resistance, all have been infected; no great surprise, since the blight is everywhere around us. But the amount of damage to the trees varies widely, thereby giving a measure of the blight resistance inherited by each tree.

Like many of his colleagues, Rich now faces the problem of finding more available and appropriate land to plant on. He told me there is a faster way to accomplish this restoration mission though: science provides a way to directly insert resistance genes into chestnut embryos. What takes him years to do using the hybridization technique could be done much quicker. But it's done in a laboratory instead of an orchard. Rich says that many people distrust genetic engineering and might not support widespread restoration if it was done that way. I suppose, somehow, inserting genes by hand-pollinating trees for years is ok though. So that's probably how it will be done. Slowly, but "naturally".

Blighting the blight

Viruses have been discovered occurring naturally in the forest which act upon and have a weakening effect on the chestnut blight fungus. European chestnuts apparently have been spared the fate of the American chestnuts by the action of these viruses on the blight there. Research in America has revealed that these viruses don't spread as quickly here as they do in Europe, for unknown reasons, so they're not helping much. But if that can be figured out, it's possible the blight will have a blight of its own, reducing its destructive power.

Also underway is a project to map the chestnut's gene sequence. When that's completed, scientists will hopefully be able to produce a tree that's entirely American, except for the addition of the few Chinese genes that give it resistance.

After all these efforts, it's entirely possible that the blight fungus itself may evolve to overcome the Chinese tree's resistance, which would be a very unhappy development.


Vase turned from BC3 chestnut




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You can see why I say these orchardists are dedicated folks. Considerable labor is required to produce and maintain the orchards throughout the growing season. Pollination must be carefully done, and meticulous records kept. Fields must be weeded. Deer, voles, and other critters must be kept away from the young trees. Nuts, once produced, must be planted and harvested each year. Young trees must be inoculated with blight fungus, and the grower must be willing to accept the fact that probably 99 percent or more of what he grows will succumb to the blight and die, despite years of care. After decades of work, and perhaps thousands of small trees grown, he may end up with a couple dozen resistant plants. Maybe. And even those that appear to be resistant may not prove out long-term. Even the Chinese chestnuts, which evolved with the blight fungus, are not totally unaffected by it; they suffer some effects, but do not die from it.

But once a seed orchard is in production, the supply of viable nuts will grow exponentially, for each planted seed can grow a tree that will produce many more seeds. So, if and when a truly resistant offspring is produced, it can be propagated rapidly.

In Massachusetts, and other states, the next looming problems are to recruit enough volunteers to manage the increasing workload as more seed orchards are planted, and to secure the required plots of land for more orchards. It's not a minor stumbling block.

Newcomers to this effort need not start at the forward-cross step as John did. They can obtain resistant seed from other growers to plant a seed orchard, and within a half-dozen or so years can be producing a seed crop of their own, hopefully for eventual widespread distribution. An acre of land is probably more than enough to get started.

If you should feel a nagging, irrational need to be a part of this motivated group of folks, a good place to start would be the TACF website. My hat's off to you.


Bodhi, on the path to enlightenment




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