Doctoral Dissertations

Orcid ID


Date of Award


Degree Type


Degree Name

Doctor of Philosophy


Entomology and Plant Pathology

Major Professor

Robert N. Trigiano

Committee Members

Denita Hadziabdic, Margaret E. Staton, Bonney Ownley, Andreas Nebenfuehr


Flowering dogwood (Cornus florida L.) and Asian dogwood (C. kousa F. Buerger ex Hance) are popular understory and deciduous ornamental trees that are mostly found throughout the temperate regions of North America, Europe, and Asia. They are valued for their showy snow-white, pink, and red bracts, red fall foliage, and colorful fruit. Ornamental dogwoods are essential horticultural crops for the economy of Tennessee, Oregon, North Carolina, and Ohio. Tennessee-based growers led the trade and accounted for 24% of US sales of flowering dogwood in 2019, whereas total dogwood sales exceeded USD31 million annually. Although more than 150 cultivars are commercially available for both species, consumer demands for specific traits of interest, such as dark red bract or foliage display, resistance to pathogens, variegated foliage, and dwarf or weeping habit, have not been satisfied. However, time-demanding dogwood cultivar development typically depends on repeated selection for desirable traits. Hence, the following challenges must be overcome: long juvenile period (3 to 5 years), self-incompatibility, inbreeding depression, and high susceptibility of flowering dogwood to two fungal foliar pathogens, dogwood anthracnose and powdery mildew. Therefore, this work was initiated to study the molecular mechanisms underlying anthocyanin and proanthocyanidin pigment biosynthesis; to enhance bract and foliage's desirable red and pink colors by using the RNA-Seq approach to enable the development of functional markers or the application of marker-assisted selection. Fully developed bracts of three cultivars of C. florida and two cultivars of C. kousa were sampled when color was maximally visible and subjected to RNA sequencing. Candidate genes CfMYB2, CfMYB3, and CkMYB2, were found to repress anthocyanin and proanthocyanidin synthesis in flowering and Asian dogwood, whereas CfMYB1 80 and CkMYB1 increased it. Two quantitative trait loci, QTLPM-7 and QTLPM-8, associated with powdery mildew resistance were identified for two consecutive years in C. florida pseudo-F2 population. Finally, recessively inherited Mildew resistance locus o (Mlo) genes, which prevent effective host cell penetration by powdery mildew, were investigated in a time-tuned transcriptome study including four C. florida cultivars of varying resistance to powdery mildew.

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