Graduation date: 2008Hop downy mildew is a devastating disease affecting hop requiring expensive fungicide applications throughout the growing season. Plant resistance is highly desirable and theorized as being decidedly quantitative with dominance and epistasis involved in resistance. An association mapping approach using a mixed-model was used to identify AFLP markers associated with the hop downy mildew resistant phenotype. New protocols for the extraction, isolation and recovery of oospores from plant tissue and soil were developed to aid in the study of the hop downy mildew oospore. In addition, logic regression was used in a mathematical model in order to test the statistical procedure’s potential for modeling epistasis. Our results suggest the hop downy mildew resistant phenotype has a broad-sense heritability of 76% with an estimated narrow-sense heritability of 49%. Mixed-model results revealed 9% of the AFLP markers to be associated with the hop downy mildew resistant phenotype. The association mapping results suggest resistance to hop downy mildew is quantitatively inherited with moderate heritability, which can be successfully investigated using mixed-models. The concentration of soil-borne oospores was 14 oospores/g soil. Germination of oospores occurred between two and eight weeks after preparation of the slides. Observations of the oospore suggested the sexual stage of this disease may play a role in over-wintering as oospores were capable of in vitro germination. In addition, MTT as a stain for downy mildew spore viability comes into question due to the possibility of a chemical reduction in the presence of NADH. Logic regression correctly identified the model which best describes the epistatic interaction of VRN-H1 and VRN-H2 and the model was synonymous with the hypothesized genetic model for vernalization in barley. The mathematical simulation using logic regression software suggested Boolean logic may be more robust when compared to general linear modeling for the identification and modeling of epistasis.