The American Chestnut FoundationÕs
Breeding Program
F. V. Hebard
Research Farms
Meadowview, VA
Fred@acf.org
www.acffarms.org

Requirements for breeding
Materials: sources of resistance and flowering American chestnut trees.
Crossing Method: for making the next generation of progeny.
Breeding Method: the sequence of crosses to perform.
Cultivation Method: for growing the trees.
 Screening Methods: for determining the blight resistance of progeny, and other traits.

Materials
American chestnut trees flower in clearcuts

Materials
Sources of blight resistance
The old USDA breeding program determined that Chinese chestnut had the most blight resistance of all the chestnut species.  In American forests, the Chinese chestnut itself cannot reach the canopy when competing with other tree species.  We were able to jumpstart our program by using two first backcrosses from the USDA & Connecticut programs.
The low levels of blight resistance in some of the large, surviving American chestnut trees might also be useful in a breeding program, which we are exploring.
Additionally, we use Japanese chestnut as a source of resistance.

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2006 Harvest in Meadowview
Slide 8
Frequency Distribution of Percent American-Chestnut RAPD Alleles at First Backcross
Slide 10
Expected distribution of canker phenotypes and genotypes in Chinese x American F2 progeny, based on observation and interpolation.
Backcrossing
Need more than one American parent
Backcrossing
Need more than one American chestnut background
Intercrossing of Third Backcrosses
How do we do it?
Slide 15
Mean RAPD Score in Individual Trees by Linkage Group
Frequency Distribution of Number of Non-Recombinant Linkage Groups in Chestnut B1
Statistics for Markers on Linkage Groups in Chestnut B1
Intercrossing of Third Backcrosses
What mating design do we use?
Intercrossing of Third Backcrosses
Possible Mating Designs: Complete Diallel
Intercrossing of Third Backcrosses
Complete Diallel, No Selfing
Intercrossing of Third Backcrosses
Half Diallel, No Selfing
Intercrossing of Third Backcrosses
 Disconnected Partial Half Diallels, No Selfing
Intercrossing of Third Backcrosses
 Disconnected Partial Half Diallels, No Selfing
Two Parents per Diallel
Intercrossing of Third Backcrosses
 Connected Partial Half Diallels, No Selfing
Two Parents = Circular Mating Design
Slide 26
Intercrossing of Third Backcross F2s
Half Diallel, No Selfing, Two Parents per Diallel
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Intercrossing of Third Backcross F3s
 Half Diallel, No Selfing, Two Parents per Diallel: Inbreeding Coefficients
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Conclusions
Two progeny per B3 family gives lower inbreeding than one
At least nine to ten B3-F2 progeny are needed per B3 family to capture most alleles
If each of those nine to ten sets of B3-F2 progeny is segregated in a separate orchard, inbreeding at F4 is reduced
Inbreeding is not strongly affected by available Òmating designs,Ó in part because we use open pollination
The American Chestnut FoundationÕs breeding program will yield adequate effective population sizes (although the projections have a number of assumptions that will not hold true, decreasing the projected Ne)

Cultivation Method
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Number of Trees at Meadowview in 2006
Number of B3s by State in 2006
Resistance
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Resistance
 Demonstration of statistically significant differences in canker length on American chestnut for virulent isolates of Cryphonectria parasitica
Slide 51
Resistance
Resistance
Slide 54
Blight-resistant Chinese to American
B2-F2, 5 years old, 2 years after inoculation with Cryphonectria parasitica.
Slide 56
Blight-Resistant Clapper B3-F2
Chestnut Blight Resistance Rating Scheme
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"Blight-resistant ÔClapperÕ x Ô..."
Blight-resistant ÔClapperÕ x ÔGravesÕ ÒB2-F2,Ó 15 years old, inoculated 13 years ago.
Obtaining trees like this suggests it should be possible to backcross the blight resistance of Chinese into American chestnut.