American Chestnut II

A couple of posts ago I wrote about how the American Chestnut tree was the dominant tree in the eastern forest until it was all but wiped out by chestnut blight at the turn of the 20th Century. I also talked about the efforts of The American Chestnut Foundation (TACF) to restore the tree by cross-breeding it with the blight resistant Chinese Chestnut. Finally, I said that it was my goal to obtain some blight resistant trees, grow them, plant their seeds, and donate the new trees to individuals and organizations to promote American Chestnut reforestation efforts.

Looks like I got a little ahead of myself. TACF is very close to its goal of developing a blight resistant hybrid tree that is 94 percent American Chestnut, but not quite there.

After further research I learned that TACF’s founder, Dr. Charles Burnham, proposed a methodology of breeding to incorporate blight resistance into the American Chestnut. The technique is called backcross breeding.

I’m not sure if I ever took a biology course in high school or college. At least I don’t recall doing so. I know enough about genetics and breeding to have fathered two children, and I attribute that to a lot of practice. 

Fortunately, there is a convenient diagram on the TACF website that explains backcross breeding. The first step is to cross an American Chestnut with a blight-resistant Chinese Chestnut. This produces an F1 hybrid which is 50 percent American Chestnut. An F1 hybrid is then crossed with an American Chestnut to produce a BC1 hybrid that is 75 percent American Chestnut. I can only guess that BC1 stands for first generation back bred Chestnut.

Now remember that the goal is (a) to produce a disease resistant tree and (b) to have enough disease resistant trees with different lineage to promote the necessary genetic diversity to sustain a robust population. This means that it’s not enough to produce one F1 hybrid. Many F1 hybrids have to be produced, all with different parents. The same is true with the BC1 hybrids, as well as for all succeeding generations.

Moreover, each generation of trees must be tested to see if they have acquired any blight resistance. Trees that do not show any degree of blight resistance are removed from the program, and only resistant trees are used to breed the next generation. Trees are tested for blight resistance by inoculating them with a weak strain and a strong strain of the blight fungus. This can only be done when the tree is 5 to 8 years old. After inoculation it takes 11 months to determine whether the tree has acquired some resistance to the blight. TACF’s website says that with excellent care, TACF is able to complete a generation in six years for less.

BC1 trees that show blight resistance are bred with American Chestnuts to produce a BC2 generation. Resistant BC2 trees are bred with American Chestnuts to produce a BC3 generation. Resistant BC3 trees are then bred with other resistant BC3 trees (this is called an intercross) to produce a BC3F2 generation. Resistant BC3F2 trees are bred with other resistant BC3F2 trees, to produce a BC3F3 generation that is 15/16 or 94 percent American Chestnut. TACF calls the BC3F3 hybrids Legacy Trees. TACF states that the Legacy Trees are “expected to show a high level of blight resistance in initial forest test-plantings.”

The project started in earnest in 1989. Since 2005 TACF has harvested increasing numbers of seeds from the Legacy Trees. These seeds are called Restoration Chestnuts 1.0. In 2009 the first of these Restoration Chestnuts were planted in real forest environments. It is expected that some of these trees will succumb to the blight, but others will prove resistant. Further breeding, both artificial and natural, of the progeny of these trees will, it is hoped, produce trees that can reproduce, thrive, and spread on their own.

As you can see, bringing back the American Chestnut is a massive project requiring numerous planting sites throughout the tree's natural range from Maine to Georgia, and from the Piedmont plateau in the Carolinas west to the Ohio Valley.

Back to me. A Management Forester for the Georgia Forestry Commission gave me the name of Dr. Martin Cipollini of Berry College in Rome, Georgia, and said that he is the leading expert on the American Chestnut tree in the southern Appalachians. He is also intimately involved in TACF’s Chestnut breeding program. I emailed Cipollini about my interest, and he sent me forms to complete that will allow my property to serve as a test orchard where a few BC3F3 trees will be planted to test whether it’s a good place to grow Chestnut trees. If it is, then my property will be considered for one of several types of orchards/plantings.

Some of these plantings are beyond my resources. For example, a restoration planting involves approximately 1400 trees, three or more acres, and a 30 year commitment. I have acres, but it’s questionable whether I have the time. Besides, I want to grow something other than trees on my property. A few rows of corn, beans and peppers might be nice.

So there you have the current state of efforts to restore the American Chestnut to its former glory. Keep your fingers crossed that my property is good for growing Chestnut trees and that the BC3F3 hybrids I receive turn out to be blight resistant. I know this probably makes me a dweeb, but I’m excited. They make jokes about people sitting around and watching the grass grow. I’ll be sitting around watching trees grow.

Finally, here’s my funny chestnut story. Many years ago when I was dating Meredith I wanted to roast some chestnuts for her. I did not have a roaring fire, but my small apartment had an oven. I couldn’t remember whether you were supposed to put a slit in the chestnuts before you roasted them. I didn’t want to ruin all of them so I only slit half of them. I popped them in the oven and turned on the heat. A few minutes later loud explosions began coming from the kitchen. It sounded like grenades were going off. We hit the floor, and I low crawled into the kitchen. The chestnuts that had not been slit were exploding in the oven like giant kernels of popcorn. When I opened the oven door, I was met with a barrage of chestnut shrapnel. I’m lucky I didn’t lose an eye.

Moral of the story: Slit your chestnuts before you roast them. Second moral of the story: Forget the chestnuts if you’re trying to score with a woman; a nice meal at a decent restaurant is so much more effective and safe.