Sandy Anaganostakis of the Connecticut Agricultural Experiment Station came to town with 20 American chestnut trees with bred resistance to the devastating disease, chestnut blight. The trees have since been planted by volunteers, led by Bill Sachs, in local parks and preserves. For those who missed the talk Sandy gave at Mountain Lakes House during her visit, here are some notes:
Sandy has been studying American chestnut blight since 1968--a passion that shows no sign of flagging. While devoting her life to bringing back the American chestnut as a timber tree, she loves all types of chestnuts--American, Japanese, Chinese, European, and the closely related chinquapins.
She began by taking us back 13,000 years, to the end of the last ice age, when the American chestnut was likely limited to a small area in what is now Tennessee. As the glaciers receded, the chestnut spread across the east.
American chestnut was the perfect timber tree. It grew straight and tall, and was highly resistant to rot. It was the main wood used for telephone poles and fencing in the east. Chestnut was the quickest to regrow after a virgin forest was cut down. Shading out other species, it became the dominant tree in second growth forests.
The first imported disease affecting American chestnuts was not chestnut blight but something called Ink disease, which hitchhiked over from Portugal on cork trees around 1824. It's a deadly disease, but can't survive the colder winters of the northern U.S.
Chestnut blight likely came to this continent around 1876, when Japanese chestnuts began being imported. It spread quickly through the eastern U.S. In Connecticut, Sandy's home state, it spread statewide in just four years, from 1908 to 1912. The blight essentially stripped American forests of the chestnut tree, but did not kill the roots. The species literally "went underground", sending up shoots that would grow for some years before being infected by the fungus. One can still find this sort of sprouting in the woods.
The disease later spread to Europe, arriving in Italy in 1938. In 1951, a European scientist discovered that some chestnuts in Italy were showing a different reaction to fungus, exhibiting swollen cankers. Trees with this sort of canker were able to grow despite the presence of the blight.
When Sandy heard about this less virulent strain in 1973, she contacted the scientist and helped identify the virus that was causing the reduced virulence. This was a particularly important discovery because the virus can be applied to American chestnuts to reduce the impact of the blight fungus.
Sandy's approach to reintroducing the American chestnut is not to plant whole forests with resistant varieties, but instead to preserve the genetic diversity by planting a few specimens with bred resistance into an area where there are remnant populations of the pure native species. By treating the non-resistant pure natives with the virus that reduces the disease's virulence, a mix of bred and pure species can survive and cross-pollinate.
I asked about the potential for identifying the gene in asian chestnut species that makes them resistant to the fungus, and then inserting that gene into American chestnuts. She said researchers have found three genes associated with resistance, which makes genetic modification more difficult. It's her experience that the traditional method of breeding resistance is actually faster than doing genetic modification in the lab, and will yield better results. The added benefit is that she gets to work outside, rather than in a lab.
As if the introduced diseases were not enough of a handicap on the American chestnut, someone smuggled plant material into the U.S. in 1974 that included an exotic insect called the chestnut gall wasp. The wasp spread through Georgia, got accidentally transported to Cleveland, Ohio, and is now heading towards the northeast from those two directions. Though there are parasites that prey on the wasp, Sandy is worried about its potential impact on efforts to restore the American chestnut to the eastern forest.
The fungus that causes chestnut blight infects oaks and eucalyptus as well.
Bill Sachs tells me the chestnuts we can buy for eating come mostly from Italy. The American chestnut is smaller but sweeter. Sandy mentioned the "Sleeping Giant" variety that makes particularly good nuts for eating, and is partly American.