Poster: Diseases of Plants: Disease Detection & Diagnosis
509-P
Development of a quantitative PCR assay to quantify resistance to Diaporthe helianthi and Diaporthe gulyae in sunflower
T. OLSON (1), F. Mathew (1), A. Adhikari (1), B. Kontz (1), L. Marek (2); (1) South Dakota State University, Brookings, SD, U.S.A., (2) Iowa State University, Ames, IA, U.S.A. / USDA-ARS
In the U.S., Phomopsis stem canker was first detected in 1983, but it was not until the 2010 epidemic in Minnesota, North Dakota, and South Dakota that two pathogens, Diaporthe helianthi and Diaporthe gulyae were identified as the causal agents. At this time, no commercial hybrids are available that have complete resistance to the two pathogens. The objectives of this study were to (1) develop quantitative polymerase chain reaction (qPCR) assays for quantification of D. helianthi and D. gulyae from sunflower and (2) evaluate sunflower germplasm for resistance to the two pathogens using qPCR assays. The primers and probes for the two qPCR assays were designed from the translation elongation factor region for amplification of D. helianthi and D. gulyae. To evaluate sunflower germplasm for resistance to Diaporthe spp., 54 sunflower genotypes from 9 different countries were screened for resistance using the stem-wound method in the greenhouse. Disease severity was evaluated 14 days after inoculation using a 0-5 rating scale from Mathew et al. (2015). Preliminary results suggest significant differences among genotypes in their resistance to D. helianthi and D. gulyae; PI 561918 (HA 378) appeared to be less susceptible to the two pathogens than the susceptible check ‘HA 288’. The qPCR assays developed in this study will be used to compare genotypes for resistance to D. helianthi and D. gulyae by quantifying the levels of pathogen DNA present in them after inoculation.