Date of Award


Document Type


Degree Name

Master of Science (MS)


Plant and Environmental Science

Committee Chair/Advisor

Dr. Ksenija Gasic

Committee Member

Dr. Christopher Saski

Committee Member

Dr. Guido Schnabel


Armillaria Root Rot (ARR) is a significant replant disease threatening the future of the United States stone fruit industry. Economic loss in South Carolina peach orchards is estimated to be $8M annually due to approximately 3-4% of annual tree deaths caused by ARR on replant sites. Management solutions are insufficient and can at best extend the life of the orchards on replant sites. The only solution to solving the ARR problem, apart from abandoning the replant site for peach production, is planting orchards on ARR-resistant rootstock. Significant progress has been made towards providing growers with genetically resistant rootstock, however, for various reasons, none of them so far have been widely adopted by growers. Breeding efforts have focused on identifying sources of tolerance to ARR, and less on the pathogen-plant interaction. Therefore, much is still unknown about how ARR fungal pathogens infect hosts with different ARR tolerances. Gene expression in Armillaria mellea and Desarmillaria caespitosa, two organisms causing ARR of important specialty crops in the United States, was investigated while infecting susceptible and tolerant Prunus hosts. By creating de novo transcriptome assemblies for both A. mellea and D. caespitosa, obtained under the pathogen’s interaction with Prunus hosts, 224 fungal effector genes were expressed by A. mellea, and 72 fungal effector encoding genes were expressed by D. caespitosa. Fungal effector encoding genes identified in both A. mellea and D. caespitosa exhibited a host-dependent nature of expression. Additionally, genes coding for cell wall-degrading enzymes (CWDEs) from both A. mellea (45) and D. caespitosa (19), with similar expression patterns exhibited by fungal effector genes were detected.

The results of this work advance our understanding of the fungal pathogens A. mellea and D. caespitosa and how they interact with Prunus hosts. The findings presented here lay the foundation for future research in better understanding ARR fungal pathogens and will complement host tolerance information in the development of genetically resistant rootstock.

Available for download on Saturday, May 31, 2025