Klug, Hope; Kovach, Margaret; Kuhn, Stephen
University of Tennessee at Chattanooga
Place of Publication
Phytophthora root rot (PRR), caused by the oomycete Phytophthora cinnamomi Rands, is a formidable obstacle to the restoration of Castanea dentata Marsh. commonly known as the American chestnut. Genetic resistance to PRR has been observed in Asian species of chestnut including C. mollissima Blume, and in interspecific hybrids between C. mollissima and C. dentata. We hypothesized that root rot resistance alleles would segregate in a 1:1 ratio within progeny of crosses between PRR resistant F1 hybrids and PRR-susceptible American chestnut trees (first-backcrosses), and that PRR resistance could be successfully passed down to all families of first-backcross hybrids. To test these hypotheses, we planted seeds of 15 first-backcross (BC1) hybrid chestnut families, and seeds of C. mollissima, C. dentata, and C. henryi (as controls) in a randomized complete block design in five large planting containers. Some of the American chestnuts used to produce the BC1s were naturally occurring C. dentata; others were third- and fourth-backcross hybrids previously selected for blight resistance. Seedlings in each container were inoculated with P. cinnamomi cultures that we isolated from soil samples of symptomatic orchards. Percent resistance to root rot within each family was measured using a visual rating of root necrosis six months post inoculation. Results reveal that we had resistant trees in every family with resistance ratios close to expected for most families. All individuals displaying root rot resistance were planted in an experimental orchard for further evaluation, as part of the ongoing efforts of the American Chestnut Foundation to breed American chestnut hybrids with both blight and root rot resistance. We observed C. henryi to demonstrate 100% resistance to root rot, suggesting it may be a another valuable source for PRR resistance alleles; to our knowledge, this is the first report of PRR resistance in C. henryi.
Thanks to: Project Director: Dr. Hill Craddock Departmental Examiner: Dr. Hope Klug Departmental Examiner: Dr. Margaret Kovach Liaison, Departmental Honors Committee: Dr. Stephen Kuhn Research assistance: Matthew Taylor Perkins Kirsten Hein
B. S.; An honors thesis submitted to the faculty of the University of Tennessee at Chattanooga in partial fulfillment of the requirements of the degree of Bachelor of Science.
Robinson, Anna C., "Measuring Phytophthora resistance phenotypes in segregating testcross families of hybrid American chestnut trees" (2016). Honors Theses.