PowerPoint Presentation - The American Chestnut Foundation’s Breeding Program

• C x A

• ¯

• F1 x A

• ¯

• B1 x A

• ¯

• B2 x A

• ¯

• B3 x B3

• ¯

• B3-F2 x B3-F2

• ¯

• B3-F3

Expected Proportion

Chinese

1/2

1/4

1/8

1/16

Year Cross Made

1930s

1940s

1989-1995

1994-2002

1999-2009(estimate

2005-

Backcrossing

•First, American and Chinese chestnut trees are crossed with each other.

•The progeny from this first cross are then backcrossed to American chestnut.

•Each cycle of backcrossing reduces the fraction of Chinese genes by a factor of one half.

•Finally, backcrosses are intercrossed to yield progeny that will breed true.

•Blight resistance is retained by inoculating progeny and selecting resistant ones.

More than one American parent is used at each backcross to avoid inbreeding. One set of American parents constitutes a line, the different Americans are denoted A1 to A4 below.

C x A1

F1 x A2

B1 x A3

B2 x A4