A greenhouse method to evaluate sunflower quantitative resistance to basal stalk rot caused by Sclerotinia sclerotiorum

Authors: Underwood, William; Misar, Christopher; BLOCK, CHARLES - Iowa State University; GULYA, THOMAS - Retired ARS Employee; TALUKDER, ZAHIRUL - North Dakota State University; Hulke, Brent; MARKELL, SAMUEL - North Dakota State University

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/14/2020
Publication Date: 12/2/2020
Citation: Underwood, W., Misar, C.G., Block, C., Gulya, T.J., Talukder, Z., Hulke, B.S., Markell, S. 2020. A greenhouse method to evaluate sunflower quantitative resistance to basal stalk rot caused by Sclerotinia sclerotiorum. Plant Disease. 105:464-472. https://doi.org/10.1094/PDIS-08-19-1790-RE.
DOI: https://doi.org/10.1094/PDIS-08-19-1790-RE

Interpretive Summary: Basal stalk rot of sunflower caused by the fungal pathogen Sclerotinia sclerotiorum is an economically important disease affecting sunflower production in the north central U.S. growing region. Resistance to this disease is genetically complex, involving many genes that each contribute small effects to the overall level of resistance. Because of this genetic complexity, accurate and rapid procedures for evaluating resistance to the disease are crucial to successfully conduct genetic mapping experiments and develop genetic markers that will facilitate improved breeding for resistance. Existing procedures for evaluating sunflower resistance to this disease were insufficiently precise and excessively laborious and time-consuming. In this study, we developed and validated a new procedure to evaluate experimental sunflower lines for resistance to basal stalk rot. This procedure, conducted in the greenhouse, is more accurate, less labor-intensive, and more rapid than previous methods. Importantly, the results of evaluations using the new greenhouse procedure were highly correlated with field observations. These improvements will facilitate more rapid progress in breeding to improve sunflower resistance to this important disease.

Technical Abstract: Resistance of sunflower to basal stalk rot caused by the fungus Sclerotinia sclerotiorum is quantitative, controlled by multiple genes contributing relatively small effects. Consequently, artificial inoculation procedures allowing for sufficient throughput and resolution of resistance are needed to identify highly resistant sunflower germplasm resources and to map loci contributing to resistance. The objective of this study was to develop a greenhouse-based method for evaluating sunflower quantitative resistance to basal stalk rot that would be simple, space- and time-efficient, high throughput, high resolution, and correlated with field observations. Experiments were conducted using five-week-old sunflower plants and Sclerotinia-infested millet seed as inoculum to assess the impact of pot size and temperature and to determine the most favorable inoculum rate and placement. Subsequently, an additional experiment was performed to assess the correlation of the greenhouse inoculation procedure with field results using a panel of 32 sunflower genotypes with known field response to basal stalk rot previously determined in multi-year, multi-location artificially-inoculated trials. Experimental observations indicated that the newly-developed greenhouse inoculation procedure provided improved resolution to identify highly resistant genotypes and was strongly correlated with field observations. This method will be useful for screening of sunflower experimental and breeding materials, disease phenotyping of genetic mapping populations, and evaluation of resistance to different pathogen isolates.