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ARS Home » Plains Area » Fargo, North Dakota » Edward T. Schafer Agricultural Research Center » Sunflower and Plant Biology Research » Research » Research Project #430556

Research Project: Identification of Sclerotinia sclerotiorum Virulence Determinants Relevant to Infection of Multiple Host Plants by Association Mapping

Location: Sunflower and Plant Biology Research

Project Number: 3060-21220-031-16-S
Project Type: Non-Assistance Cooperative Agreement

Start Date: Aug 1, 2016
End Date: Dec 31, 2020

The objective of the proposed project is to identify genetic factors contributing to virulence of S. sclerotiorum on sunflower, dry bean, and soybean. The project aims to improve our understanding of the processes underlying disease development and facilitate novel strategies to improve tolerance to Sclerotinia diseases in sunflower and other host plants. Specific objectives for the duration of the project are to: 1) Evaluate the virulence of a large and diverse collection of S. sclerotiorum isolates on stalk and head tissues of sunflower. 2) Perform genotyping-by-sequencing to improve marker density for previously genotyped isolates and to genotype additional isolates to facilitate association mapping. 3) Conduct association mapping to identify candidate genetic factors in S. sclerotiorum that contribute to differences in isolate virulence on sunflower, dry bean, and soybean. 4) Evaluate candidate S. sclerotiorum genes for their role in virulence using two strategies: A) Direct knockout of the gene using gene replacement and subsequent evaluation of mutant S. sclerotiorum strains for virulence on multiple hosts and, B) Host-induced gene silencing (HIGS) to target candidate S. sclerotiorum genes by expression of small interfering RNAs in the model plant Arabidopsis thaliana.

Plant-pathogenic microorganisms utilize protein, small molecule, and small RNA effectors to suppress defenses and manipulate cellular and tissue physiology in their host plants to cause disease. The ongoing identification of pathogen effectors and characterization of their functions and host targets is paving the way toward new solutions for the control of plant diseases. Relative to other fungal phytopathogens, little is currently known about effectors or other virulence factors used by S. sclerotiorum to cause disease on the wide range of susceptible plants infected by this pathogen. This deficit in knowledge of the biology and infection processes of the pathogen constrains our ability to rationally direct research and devise strategies to improve plant resistance. We hypothesize that, like other fungal phytopathogens, S. sclerotiorum utilizes effector molecules and other virulence factors to cause disease on susceptible plants. Here, we propose an approach to identify important virulence determinants in S. sclerotiorum relevant to infection of sunflower by exploiting natural variation in the virulence of diverse S. sclerotiorum isolates and using association mapping to determine genetic factors underlying the observed variation in virulence. Our approach encompasses four aims. We will phenotype a large collection of diverse S. sclerotiorum isolates for virulence on two sunflower tissues (stalk and head), genotype the isolates using genotyping-by-sequencing to generate a high density of polymorphic markers, and conduct association mapping to identify markers that correlate with differences in isolate virulence. We will subsequently evaluate candidate S. sclerotiorum virulence genes by a reverse genetic approach with evaluation of virulence on affected plants and by a novel host-induced gene silencing approach in the model plant Arabidopsis thaliana.