CT Chapter of The American Chestnut Foundation. Illustration by Dr. Fred Paillet.
The TACF Breeding Program - Breeding in Blight Resistance  

Dr. Charles Burnham on left

[click image for larger version]

TACF was founded in 1983 by a group of prominent plant scientists, including Nobel Prize-winning plant breeder Dr. Norman Borlaug; Dr. Peter Raven, Director of the Missouri Botanical Garden; independent chestnut researcher Philip Rutter; and the late Dr. Charles Burnham, the eminent Minnesota corn geneticist. In 1989 TACF established the Wagner Research Farm, a breeding station in Meadowview, Virginia, to execute the backcross breeding program. A second research farm in Meadowview was donated to TACF in 1995, and a third Meadowview farm was purchased in 2002. Dr. Burham is shown in photo at left. Dr. Burnham is credited with having developed the backcross breeding program for which TACF was developed to implement. Dr. Burnham wrote the following article published in 1989 which describes the breeding process.

The Pennsylvania Chapter of TACF has an excellent article explaining back-cross breeding should you be interested in further research.

Author: Dr. Charles Burnham - 1989
From the TACF Journal Vol 4 Issue 1

The current American chestnut breeding program is using the Chinese chestnut as the best source of resistance. The blight fungus fails to grow at the point of infection. The hybrid between the two species is moderately resistant, more resistant than the American, but less resistant than the Chinese chestnut. Resistance is incompletely dominant. By crossing that hybrid back to the American chestnut and following with successive back-crosses to the American chestnut, using blight-resistant selections each time for the next back-cross, the American chestnut is recovered automatically, and at the same time resistance to the blight is being added by selection. The third back-crosses are, on the average, 15/16 American chestnut and some will have the gene(s) for resistance derived from the Chinese chestnut, but only from one parent and, consequently, are only moderately resistant. Progeny from crosses between those moderately-resistant selections will include some that have received the gene(s) for resistance from both parents. They are homozygous for those genes are expected to be as resistant as the Chinese chestnut. They will "breed true" for resistance.

Corn breeders find that third back-cross progeny* are indistinguishable from the recurrent parent. In the current chestnut breeding program second back-crosses are now growing, one back-cross away from the final back-cross and the final two step, i.e., one to produce the true-breeding, highly resistant homozygotes, and one for increasing them.

The goal of the present program is not a single-tree cultivar, but breeding populations - ultimately, ones that will be adapted to different plant growth regions.

Next >>    Read about how The American Chestnut Foundation grew blight resistant trees.

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