Location: Sunflower and Plant Biology Research2016 Annual Report
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.
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.
Milestones listed in Question 2 comprise the National Sclerotinia Initiative Strategic Plan http://www.ars.usda.gov/SP2UserFiles/ad_hoc/54000000WhiteMoldResearch/SI-Strategic-PLan_%202017-2021_v1_0_Jan16.pdf Each milestone was addressed in FY2016 by components of the 19 cooperative agreements and ARS projects funded from the Initiative. Research is ongoing in all areas and substantial progress has been made in Epidemiology and Disease Management and Variety Development & Germplasm Enhancement. Pathogen and Host Genomics research also resulted in significant progress, but substantial efforts are still needed in genome sequencing of the pathogen and gene profiling of susceptible and resistant crops. Pathogen Biology and Development research is ongoing, but additional efforts are needed to identify disease infection processes and to characterize virulence among disease genotypes.
1. Candidate genes for white mold resistance for U.S. agriculture. The National Sclerotinia Initiative (NSI) employs an integrated and collaborative approach to guide research on the effective development of diagnostic technologies, disease management systems, genomic resources, and crop germplasm exhibiting durable resistance to Sclerotinia sclerotiorum, also known as white mold. Over the past several years, the USDA National Sclerotinia Initiative in Fargo, North Dakota in conjunction with Michigan State University, North Dakota State University, and Florida State University has identified a variety of quantitative trait loci (QTL) for white mold resistance/avoidance in sunflower, pea, and arabidopsis among others. Now candidate genes underlying the QTLs are being cloned and characterized. For example, among the 41 genes within a QTL region in common bean, a gene encoding a protein involved in vacuolar protein trafficking and effector triggered pathogen immunity was identified. Identification of genes, especially those involved in early effector recognition is key to understanding the molecular mechanisms that control white mold tolerance in susceptible broadleaf crops, and is critical to developing genotypes that express high levels of tolerance to the pathogen. The strategic characterization of key gene for resistance and their use in germplasm enhancement, both public and private, will reduce losses to this devastating disease and help sustain the competitiveness of U.S. canola, pea, lentil, chickpea, common bean, soybean, and sunflower producers in domestic and global markets.
2. Developing predictors for Sclerotinia disease development. Fungicides are often used to reduce the incidence of sclerotinia disease in the absence of fully resistant germplasm for susceptible broadleaf crops. The timing of fungicide application is critical to optimize their effectiveness against Sclerotinia diseases such as white mold and sunflower head rot. The National Sclerotinia Initiative (NSI) in collaboration with the North Dakota Agricultural Experiment Station have devised methods for determining disease development for soybean, dry bean, and sunflower to increase the efficacy of applied fungicides. For example, under moist conditions during full bloom and early pod development, soybeans developed high levels of Sclerotinia, while after full bloom and during mid to late pod-fill the soybeans exhibited sharply delayed disease development. From this research it was determined that the optimal application timing of the foliar fungicide coincided with the early full bloom stage of development. However, the disease control and soybean yield responses to applying a fungicide were greatly reduced when wet conditions did not occur until after the bloom period. Sclerotinia disease development information aids producers throughout North Dakota to effectively time the application of fungicides to reduce yield losses due Sclerotinia diseases.
3. Aggressiveness of Sclerotinia isolates. The plant pathogen Sclerotinia sclerotiorum is the causal agent of white mold diseases on broadleaf crops such as sunflower, soybean, common beans, peas, and lentils. It has been noted that some isolates are more aggressive than others in inducing disease on the crop. As such, the National Sclerotinia Initiative (NSI) in collaboration with North Dakota State University and the University of Nebraska have collected isolates from various crops in the U.S. to characterize aggressiveness in natural populations. To further understand aggressiveness, researchers developed single nucleotide polymorphism (SNP) markers at unique loci across the Sclerotinia genome. Using the markers and a genetic technique called association mapping, they identified five candidate genes underlying virulence/aggressiveness of Sclerotinia. Validation of these candidate genes sets the stage to identify molecular mechanisms that regulate the host-pathogen interaction for this widespread and devastating plant pathogen.
4. Stalk rot resistance in sunflower wild relatives. Sclerotinia sclerotiorum or white mold is the causal agent of a serious sunflower disease epidemic worldwide causing stalk, head and, mid-stem rot. Sunflower and its wild relatives are native to North America and are distributed over a large geographic area, which exposes them to a wide range of environmental conditions and disease organisms that coevolved with the crop, providing the opportunity to discover disease resistance genes in natural populations. The genetics of resistance to stalk rot is quantitative, requiring many genes for control, which complicates the breeding effort. ARS research scientists at Fargo, North Dakota discovered high levels of resistance to stalk rot in several perennial crop wild relatives including Maximillian, Nuttall’s, California, woodland, and muck sunflowers. Six progeny families have been developed that have a disease incidence three times lower than the most resistant hybrids. These germplasms will provide sunflower breeders and producers with additional genes to diversify the genetic base of sunflower and will provide additional control for a major disease that limits production, helping to sustain sunflower production in an environmentally friendly manner.
5. Transformation system in sunflower for Sclerotinia resistance. Sunflower is one of the few remaining crops that lack a suitable transformation and regeneration system. A reliable sunflower transformation system for Sclerotinia resistance can lead to generation of non-transgenic sunflower through new technologies such as the CRISPR/CAS9, which is a new genomic DNA editing tool. The USDA National Sclerotinia Initiative in Fargo, North Dakota in conjunction with The Ohio State University developed a transformation protocol using a low Agrobacterium inoculum level with an extended period of co-culture with the sunflower plant material. Moreover, the general approach has application to all plants. The protocol promotes efforts to identify alternative response to Sclerotinia and identify genes related to host plant response to this serious soil borne pathogen of many broadleaf crops.