Wednesday, August 22, 2012

The Return of the American Chestnut?

Once a dominant member of the forest canopy in much of the Eastern US, the American Chestnut (Castanea dentata), was infected by the Chestnut Blight fungus (Cryphonectria parasitica), which was introduced from Asia by the Bronx Zoo.  The disease kills upper part of the tree by infecting the bark, but leaves the rootstock intact, which often re-sprouts, only to be reinfected before it grows back into a tree.  There are several such rootstocks in my neighborhood.

Now, scientists in New York claim to have produced a genetically modified American Chestnut (with a little Chinese blood), that is resistant to the fungus:
...The efforts were picked up again in the 1980s by scientists and plant lovers who founded the American Chestnut Foundation. They applied a new method, called backcross breeding, which was first used for corn that imparts preferable traits over several generations.

The foundation started planting their new chestnuts—one-sixteenth Chinese and the rest American—in Virginia in 2006. More than 100,000 of the trees are growing across 19 states, with plans for millions more in what the group calls the country’s largest ecological restoration effort. Thousands of trees were inoculated with the fungus in June 2011, with 20% showing strong resistance and 40% with a more moderate amount, foundation president Bryan Burhans said. Scientists will select for the strongest resistances when breeding future generations, he said.
My question is, when the hybrids have achieved a sufficient level of resistance that they can be released into the wild, will managers have reservations about introducing a genetically modified tree into native forests?  Just because it looks the same and produces the same fruit as the original native chestnut doesn't mean it will behave the same in the wild.

Take the example of Phragmites australis, the Common Reed.  Native to the US, it was a minor player in marsh systems until an Eurasian variety was accidentally introduced.  The non-native variety, although almost identical in form to the native varieties, was much more vigorous in growth, and colonizes a much wider variety of habitats, and has become a serious nuisance.  Could the Asian-American hybrid Chestnut become a similar problem?  Unlikely, but not outside the realm of possibility.  

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