Date of Award
Doctor of Philosophy
Plant, Soil and Environmental Sciences
B. S. Pickett
Eyvind Thor, James Hilty, Gordon Hunt
American chestnut (Castanea dentata Borkh.) was a highly valued forest species in the Appalachian region prior to introduction of the chestnut blight fungus (Endothia parasitica (Murr.) A. & A.), which practically eliminated it. Since no control method has been devised and oriental species and hybrids are not generally satisfactory replacements, breeding resistant individuals through selection offers some hope of reestablishment. A chemical method for screening resis-tant individuals for retention in a breeding program would be of great benefit. Since phenolic compounds have been implicated in disease resistance of some cultivated crops and forest and fruit trees, this study is an initial attempt to develop a chemical screening method by studying comparative phenolic composition of five types of inner bark samples. Inner bark of individual American chestnut trees was sampled from sound and infected stems, sound roots and debudded twigs. Sound inner bark from exotic (blight resistant) chestnut individual trees was also sampled. A stepwise extraction of air-dried bark samples was carried out in a Soxhlet apparatus using four organic solvents of increasing polarity; this resulted in twenty crude extract groups. Each extract group was investigated by one- or two-dimensional thin-layer chromatography. Phenolic compounds were located by spraying chromatograms with ferric chloride-potassium ferricyanide. Over 225 phenolic components were located. In some cases components from different samples extracted with the same solvent were indistinguishable. Some components were tentatively placed into more specific chemical classes. These compounds were found to most likely be derivatives of flavonoids, catechins, leucoanthocyanins, guaiacol and vanillin acid. A distinctive difference in chromatographic pattern was noted between American chestnut sound bark extracts and infected bark extracts from the same trees. There was almost no correlation between American chestnut root bark extracts and stem bark extracts. Little correlation was noted between American chestnut and exotic chestnut extracts; only eight components were found to be indistinguishable. Several similarities were noted between American chestnut sound stem bark and debudded twig extracts from the same trees. Individual tree data indicated considerable qualitative and quantitative variation among American chestnut trees in the extractable phenolic composition of their inner bark. A method adaptable to small quantities of extract was applied to bioassays with E. parasitica. In general, bioassay results did not correspond with observed field resistance to the chestnut blight fungus. Extracts from American chestnut infected bark extracts were most inhibitory; those from root bark of the same species least inhibitory.
Barnett, Paul Edward, "A comparative study of phenolics in chestnut (Castanea), and their relationships with resistance to Endothia Parasitica. " PhD diss., University of Tennessee, 1972.