Chestnut Come Back?

[BillTre]

The American Chestnut tree used to be common in certain eastern US areas. A blight (fungal in nature) that came in to the US on an imported Chinese Chestnut. The fungus reeked havoc on the native American version. The big forests of chestnut trees are gone but some more isolated trees survived. the Chinese version is resistant to the fungus (which allowed it to get access to the American trees). The Chinese version is shorter, so, not so much a canopy tree as the American Chestnut is.
There is a long standing breeding program of making hybrid crosses between the American and Chinese versions. This gives you a 50-50 mix of genes from the two parents. They then take the 50-50 hybrids and make back crosses to one of the parents. This gives you a 75-25 mix of genes. Back crosses like this can go on indefinitely. It will (on average) reduce the percentage of genes in the off spring by half of what the previous generation by half.

At each step a variety of selections are possible that should enhance fungal resistant genes:

• success against possible exposure to the fungus
• success against intentional exposure to the fungus
• using sequence based markers to identify genes in individuals with greater resistant. this will allow for directed breeding since the sequence will let you see which individuals have resistance aiding genes.
• selection for traits (like height, a trait of the American version that is desired in the hybrids).

This has been going on for several generations by a decentralized collection of people trying to set up little test forests.
This Science Friday podcast talks about this ongoing program.