Location: Sunflower Improvement Research
2023 Annual Report
Objectives
Objective 1. Coordinate the development of a Sclerotinia initiative for expanded research to control this devastating disease which affects canola, sunflowers, soybeans, edible dry beans, lentils, peas and other crops. Research should be coordinated with interested ARS, state, and industry cooperators and administered through specific cooperative agreements. Planning workshops and annual meetings involving interested parties will be organized throughout the funding period. (NP 303, C3, PS 3A)
Objective 2. Characterize resistance to Sclerotinia diseases in relevant crops, and support development of innovative diagnostic technologies, disease management systems, genomic resources, and crop germplasm exhibiting durable resistance to Sclerotinia sclerotiorum. (NP 303, C3, PS 3A)
Subobjective 2A: Identify genetic loci contributing to basal stalk rot resistance by conducting a genome-wide association study (GWAS) of a cultivated sunflower diversity panel.
Subobjective 2B: Determine the transcriptional responses to basal stalk rot infection in resistant and susceptible sunflower lines and compare changes in gene expression patterns to those observed in response to Sclerotinia infection for soybean, pea, canola, and sunflower head rot.
Subobjective 2C: Evaluate experimental sunflower germplasm lines for resistance to Sclerotinia basal stalk rot and head rot to facilitate germplasm improvement.
Approach
Exotic and emerging plant diseases pose severe problems throughout the United States. Their increasing importance may be attributed to the introduction of pathogens into new geographic regions; modification of the environment that favor diseases; change in crop management practices; genetic shifts in the pathogen population; and other processes that may give them a competitive advantage.
The fungus Sclerotinia sclerotiorum causes disease and economic loss on many important crop plants. S. sclerotiorum typically causes stem rotting on susceptible crop plants such as soybean, canola, dry edible bean, pea, and chickpea. However, this fungus causes two additional forms of disease on cultivated sunflower. Head rot occurs when fungal spores land on the sunflower head, causing destruction of the head and loss of seeds, while basal stalk rot occurs when fungal mycelia invade sunflower roots, causing root rot and wilting. Though S. sclerotiorum diseases of most crops can be managed by fungicide applications, fungicides are ineffective for control of sunflower head and basal stalk rots, leaving producers few options to combat Sclerotinia diseases. Improvement of host plant resistance to S. sclerotiorum is crucial to provide US sunflower growers with resistant hybrids to minimize economic losses. Resistance to S. sclerotiorum is quantitative, controlled by many genes contributing small effects to the overall level of resistance. This genetic complexity has hampered development of crop varieties with improved resistance. Consequently, this project aims to facilitate improvement of resistance to Sclerotinia diseases. Specific objectives are to: 1) map genetic loci underlying quantitative resistance to sunflower basal stalk rot; 2) understand transcriptional responses associated with basal stalk rot resistance; and 3) evaluate sunflower experimental germplasm for Sclerotinia resistance to facilitate germplasm enhancement. Completion of these objectives will provide new knowledge of genetic loci controlling resistance to Sclerotinia diseases of sunflower, information about transcriptional responses to Sclerotinia infection, and released germplasm resources to support breeding efforts. Additionally, comparative analyses of sunflower transcriptomic data with datasets from soybean, canola, and pea will improve our knowledge of common responses to infection by this pathogen. These resources will enhance the ability of plant breeders to improve resistance to Sclerotinia diseases in commercial crop varieties and hybrids.
Progress Report
The National Sclerotinia Initiative, administered through the Edward T. Schafer Agricultural Research Center in Fargo, North Dakota, has used cooperative research to provide solutions to the debilitating effects of white mold disease on seven important crops: sunflower, soybean, dry beans, dry peas, lentils, and chickpeas. Cooperative projects were established each year with university, private research institution, and other Agricultural Research Service scientists. Research plans-of-work were requested for the fiscal year (FY) 23 funding cycle in December 2022. Almost $2.1 million in requests from 26 potential projects were received, with approximately $1.66 million available for distribution to selected plans-of-work. Proposals were reviewed and ranked by a scientific review panel. The Initiative Steering Committee met and awarded funds to 23 projects, spanning the research priority areas of Germplasm Resources & Translational Genomics, Pathogen Biology & Mechanisms of Resistance, and Disease Management & Crop Production. An annual progress reporting meeting was also held in January 2023 to discuss all the research from the past year and to establish new collaborations amongst the project cooperators. This meeting provides new ideas to the researchers and informs the commodity group stakeholders about the impact being made by the Initiative.
In-house research was also conducted as part of the Initiative. In Subobjective 2A, a sunflower association mapping population, consisting of 287 lines, was evaluated for basal stalk rot resistance with Sclerotinia sclerotiorum isolate NEB-274 in the greenhouse. Three replications were conducted in which 16 plants per line were evaluated for time to death from basal stalk rot in each experimental replication. A broad range of basal stalk rot response was observed, with mean time to plant death ranging from 8.3 days post-inoculation for the most susceptible entry to 28.5 days post-inoculation for the most resistant entry. Inbred line HA 124 was identified as the most resistant line in this diversity panel and 11 other lines exhibited very good resistance with mean time to plant death values greater than 20 days. Mapping of resistance loci by genome-wide association is ongoing. For Subobjective 2C, a total of 737 sunflower testcross hybrids were evaluated for basal stalk rot resistance in greenhouse trials to provide information for further line development and selections. Testcross hybrids exhibiting levels of basal stalk rot resistance similar to HA 124, the most resistant line identified to date, were identified. These results will be used to identify experimental germplasm lines with good basal stalk rot resistance and favorable agronomic traits for further development and potential release.
Accomplishments
Review Publications
Pedersen, C.J., Marzano, S.L. 2022. Characterization of transcriptional responses to genomovirus infection of the white mold fungus, Sclerotinia sclerotiorum. Viruses. 14(9). Article #1892. https://doi.org/10.3390/v14091892.
Pedersen, C.J., Marzano, S.L. 2023. Mechanisms of primed defense: plant immunity induced by endophytic colonization of a mycovirus-induced hypovirulent fungal pathogen. Molecular Plant-Microbe Interactions. 36(11):726-736. https://doi.org/10.1094/mpmi-06-23-0083-r.
Nieto-Lopez, E.H., Justo Miorini, T.J., Wulkop-Gil, C.A., Chilvers, M.I., Giesler, L.J., Jackson-Ziems, T.A., Kabbage, M., Mueller, D.S., Smith, D.L., Tovar-Pedraza, J.M., Willbur, J.F., Everhart, S.E. 2023. Fungicide sensitivity of sclerotinia sclerotiorum from U.S. soybean and dry bean, compared to different regions and climates. Plant Disease. 107(8):2395-2406. https://doi.org/10.1094/PDIS-07-22-1707-RE.
