First and eighth authors: USDA Forest Service, Southern Research Station, Southern Institute of Forest Genetics, 23332 Highway 67, Saucier, MS 39574; second author: American Chestnut Foundation Research Farms, 14005 Glenbrook Avenue, Meadowview, VA 24361-9703; third author: International Paper Company, Southlands Experiment Forest, 719 Southlands Road, Bainbridge, GA 31717; fourth and fifth authors: University of Massachusetts, Department of Plant and Soil Sciences, French Hall, Box 32910, Amherst 01003-2910; sixth author: 136 Atwood Research Facility, Kentucky State University, Frankfort 40601; and seventh author: Connecticut Agricultural Experiment Station, Box 1106, New Haven 06504
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Accepted for publication 25 March 1997.
A three-generation American chestnut × Chinese chestnut pedigree was used to construct a genetic linkage map for chestnut and to investigate the control of resistance to Endothia parasitica (chestnut blight fungus). DNA genotypes for 241 polymorphic markers (eight isozymes, 17 restriction fragment length polymorphisms [RFLPs], and 216 random amplified polymorphic DNAs [RAPDs]) were assayed on an F2 family consisting of 102 individuals. Of these markers, 196 were segregating as expected and, subsequently, used for primary linkage mapping. Two isozymes, 12 RFLPs, and 170 RAPDs were mapped to 12 linkage groups spanning a total genetic distance of 530.1 Kosambi centimorgans. F2 plants were evaluated for a response to E. parasitica infection by directly inoculating them with two unique fungal isolates and measuring canker expansion over a period of 3.5 months. Results were compared with the marker genotype data, thereby identifying genomic regions significantly associated with a resistance response. Single-marker or nonsimultaneous analyses of variance identified seven genomic regions that appear to have an effect on host response. Multiple-marker or simultaneous models suggest that three of these regions have a significant effect on host response, together explaining as much as 42.2% of the total variation for canker size. At each of the three putative resistance loci, alleles derived from the Chinese chestnut grandparent were associated with smaller canker size, or higher levels of resistance.
The American Phytopathological Society, 1997