2009 Annual Report
Characterize the virulence of selected isolates on partially resistant and susceptible cultivars of soybean, sunflower, canola, dry bean, pea and lentil.
The primary approach is to make a collection of isolates of the pathogen from the six crops, identify mycelial compatibility groups, use microsatellites to characterize the genetic variation and then characterize virulence of isolates representative of the clones/genetic groups on all six crops using two different methods. Two techniques will be employed to evaluate virulence:.
Genetic variation and virulence of S. sclerotiorum on six crops in the North Central Region: Sclerotinia sclerotiorum is one of the most important pathogens of field crops in the North Central USA, yet we lack an understanding of the genetic variation and virulence of currently prevalent genotypes of S. sclerotiorum in the region - a fundamental part of the overall strategy of using resistant cultivars and other controls for this pathogen. This project examines genetic variation and virulence for a set of isolates from the current population of the pathogen on canola, dry bean, field pea, lentil, soybean and sunflower. The first objective is to use mycelial compatibility groups (MCGs) and microsatellite markers to characterize genetic diversity of the pathogen from six common, susceptible crops. The second objective is to compare virulence of isolates collected from these crops on susceptible and partially resistant cultivars of all six crops when grown in the greenhouse. During fall 2008, we obtained isolates of S. sclerotiorum from four crops (canola, dry bean, soybean, and sunflower) in eleven North Central states (ND, SD, NE, MN, IA, MO, WI, MI, IN, OH, and IL). In addition, we obtained isolates from Montana, Wyoming and Colorado. We have currently screened 98 isolates from canola, dry bean, soybean, and sunflower in the Red River Valley region of North Dakota and Minnesota. For objective 2, we have completed pilot studies to compare lesion formation rates for pairs of isolates on cultivars of the six crop species (susceptible lines of canola, dry bean, field pea, lentil, soybean, and sunflower, and partially resistant lines of canola and soybean). We plan to establish an experiment comparing virulence of 20 isolates collected from each of four crops (canola, dry bean, soybean, and sunflower) on the six crops in fall of 2009, when conditions are best for inoculation in the greenhouse. We will use the information obtained from Objective 1 to select isolates with rare vs. common genotypes as well as any genotypes that appear to be associated with particular crop species. Using this unique large collection of isolates from four crop species across the North Central Region we are beginning to document the extent of genetic variation with respect to both geography and crop and link this variation to measurements of virulence across the six crop species. The National Sclerotinia Initiative contributes to the goals of ARS National Program 303 – Plant Diseases.