Craddock, J. Hill
Klug, Hope; Leasi, Francesca
University of Tennessee at Chattanooga
Place of Publication
Chestnut blight is a disease caused by the ascomycete fungus Cryphonectria parasitica in the Castanea species. The fungus uses oxalic acid (OA) to attack the tree’s cells. Castanea dentata, the American chestnut, was wiped out by chestnut blight in the early to mid-20th century, but several East Asian Castanea species appear highly resistant to the fungus. To breed resistant American type trees, screening methods are used to enable selection of interspecific hybrids. The alternative small stem assay (aSSA) is a method of screening container-grown hybrid seedlings during their first growing season by directly infecting them with C. parasitica. Some plant species use oxalate oxidase enzymes to defend themselves from fungal OA attacks. Although Castanea species do not have endogenous oxalate oxidase genes (OxO), chestnut species vary in their responses to OA. OA tolerance (measured by the browning of tissues exposed to OA solutions) appears to correlate well with blight resistance (as measured by Small Stem Assays) in chestnut species and hybrids. This knowledge was used to characterize hybrid germplasm in Castanea breeding populations in Tennessee in 2022 and 2023. Three hundred twenty-five seedlings of eighteen half-sibling hybrid families and five species, were arranged for screening in a randomized complete block design at the UTC Fortwood Street Greenhouse. Results show that screening seedlings with an oxalic acid leaf disk soak yield results that correlate strongly with results of an alternate small stem assay of the same plants. The aSSA and oxalic acid leaf disk soak assay were thus shown to be complementary methods for distinguishing blight tolerance in hybrid chestnut seedlings. All trees from the 2022 trials will be planted in an experimental orchard in Middle Tennessee for long-term observations.
First, thank you to UTC Honors for funding my research, It could not have been done otherwise. I would like to thank Dr. Hill Craddock for agreeing to be my thesis director. This thesis has taken many different turns, but it has made me into the biologist I have yearned to be. I want to thank the UTC Greenhouse crew for their weekly help! Thank you to Dr. Leasi and Dr. Klug for agreeing to be on my committee. I am very grateful for all my help at UTC. Also, I would like to thank Dr. Andy Newhouse from SUNY-ESF with his immeasurable help with developing the methods portion of my thesis. Thank you to Dr. Jared Westbrook for your help with R and statistical analysis. A final thank you to The American Chestnut Foundation for their overall conservation efforts with the American chestnut tree. It was so encouraging to receive feedback, insight, help, and advice from everyone during my year of research. I enjoyed presenting my results numerous times to the foundation.
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.
American chestnut--Disease and pest resistance; Chestnut blight; Chinese chestnut
Harden, Kaitlyn, "Oxalic acid leaf disk soak assay is a new possibility in screening for blight resistance in Castanea species" (2023). Honors Theses.