Craddock, J. Hill
Carver, Ethan; Boyd, Jennifer
University of Tennessee at Chattanooga
Place of Publication
Phytophthora root rot (PRR), caused by the oomycete Phytophthora cinnamomi Rands., is one of the two greatest obstacles to survival of American chestnut (Castanea dentata Borkh.). The other is chestnut blight, caused by the ascomycete Cryphonectria parasitica (Murr.) Barr. Developing early and reliable PRR screening methods can facilitate the efficient introgression of PRR resistance from Chinese chestnut (C. mollissima Blume.) into the populations of potentially chestnut blight resistant trees currently under development by The American Chestnut Foundation (TACF). This study tests the efficacy of a method for early identification of PRR-resistant hybrid chestnuts in a greenhouse/nursery setting. The chestnut blight resistant hybrid families studied are derived from twenty years of work by the Tennessee Chapter of TACF and represent sources of PRR resistance not previously utilized by TACF. During the midsummer months of 2016 and 2017, container-grown seedlings were inoculated with P. cinnamomi, prepared on a clarified V8 agar medium, and rice-grain or vermiculite inoculum. Root necrotic lesions were rated using a numerical scale from 0-3, with “0” representing a plant that is completely asymptomatic, “1” representing lesions on the lateral roots only, “2” representing lesions on the lateral and on tap roots, and “3” representing plants killed by PRR (Jeffers et al., 2009). Results of the 2017 were inconclusive because of problems preparing the inoculum, and extreme environmental conditions in the early winter (freeze damage to the roots in December confounded root necrosis observations in January and February). The results of the 2016 trial show, at a 0.05 significance level, statistically significant differences in the average root rating between C. mollissima and C. dentata. Significant differences were seen in the average root rating between some hybrid families, intragenerationally and intergenerationally. Six of the backcross hybrid families; were not significantly different from the average root rating in the Chinese chestnut control families. The were no statistically significant differences between generations (B1, BB1, and B3F2). Families that were interpreted to have any degree of PRR resistance are assumed to have inherited PRR resistance alleles from C. mollissima. Trees identified as PRR-resistance will be transplanted into orchard settings for further observation, and represent a population of crosses that will be utilized for future breeding and restoration efforts.
I would like to express my deepest appreciation to my thesis director, Dr. J. Hill Craddock, for his continuous support of my study and research, for his patience, motivation, enthusiasm, and knowledge. I would also like to thank the rest of my committee and co-authors, Dr. Ethan Carver, Dr. Jennifer Boyd, and Taylor Perkins, for their encouragement, insightful comments, guidance, and time spent towards my project. I am also appreciative for my friends and family who have supported me throughout this process. I wish to thank The University of Tennessee at Chattanooga, Department of Biological and Environmental Sciences faculty and staff for their help and support. Additionally, I thank The American Chestnut Foundation, University Honors Program, the Fortwood Street greenhouse crew, and the Tucker 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; Chinese chestnut
Hein, Kirsten, "Implementing early screening methods to detect resistance to Phytophthora cinnamomi in backcross Chinese-American Chestnut hybrids" (2018). Honors Theses.