Document Type

Thesis - Open Access

Award Date


Degree Name

Master of Science (MS)

Department / School

Agronomy, Horticulture, and Plant Science

First Advisor

Febina Mathew


Phomopsis stem canker is a disease that severely affects sunflower (Helianthus annuus) in the United States. From 2001 to 2015, disease prevalence has increased from 1.5% to 61%, and two new causal agents, Diaporthe gulyae and Diaporthe stewartii, have been described along with Diaporthe helianthi, which was always regarded as the main causal pathogen of the disease. At this time, options to manage the disease are limited. Currently, no commercial sunflower hybrids have resistance to all three species of Diaporthe, and no fungicides are labeled for control of Phomopsis stem canker of sunflower in the United States. To help improve management of the disease with effective diagnostics, two quantitative polymerase chain reaction (qPCR) assays were designed from the translation elongation factor region (EF1-α) of D. helianthi and D. gulyae. The specificity of the two qPCR assays was validated by examining the assays with genomic DNA of various species of Diaporthe and other plant pathogens. The detection limit of both assays was 10 ng to 1 pg of DNA. Both assays were capable of detecting D. helianthi and D. gulyae from infected plant samples, and these results were confirmed by traditional isolation of the pathogens onto potato dextrose agar (PDA). The qPCR assays also proved to be effective in genotype screening for stem resistance to D. helianthi and D. gulyae under greenhouse conditions, identifying 16 genotypes with potential resistance to D. helianthi and D. gulyae.

Library of Congress Subject Headings

Sunflowers -- Diseases and pests.
Canker (Plant disease)


Includes bibliographical references



Number of Pages



South Dakota State University



Rights Statement

In Copyright