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United States Department of Agriculture

Agricultural Research Service

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Research Project: GENETIC VARIATION AND VIRULENCE OF S. SCLEROTIORUM IN THE UNITED STATES

Location: Sunflower Research

2009 Annual Report


1a.Objectives (from AD-416)
Determine genetic variation of S. sclerotiorum from soybean, sunflower, canola, dry bean, pea and lentil in the northern part of the North Central region using DNA fingerprinting and mycelial compatibility groups.

Characterize the virulence of selected isolates on partially resistant and susceptible cultivars of soybean, sunflower, canola, dry bean, pea and lentil.


1b.Approach (from AD-416)
Sclerotinia sclerotiorum is one of the most important pathogens of field crops in the North Central USA, causing economic losses in the numerous susceptible crops grown in the northern tier of states. The diseases caused by this pathogen have been very difficult to control. There is no published information on the genetic variation of S. sclerotiorum in the North Central region of the United States that includes information on isolate virulence across crops such as soybean, sunflower, canola, drybean, pea and lentil. Understanding the genetic variation and virulence of the current isolates of S. sclerotiorum in the region is a fundamental part of the overall strategy of using resistance or other controls for this pathogen. Such information may also help explain the mixed results of field screening for resistance that has been observed over the region and the lack of correlation between field and laboratory evaluations. This research will study genetic variation and virulence of a set of isolates from the current population of the pathogen on dry bean, canola, soybean, sunflower, pea and lentil in the northern tier of states in the North Central Region. This region has the greatest concentration of the numerous crops susceptible to white mold.

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:.
1)a novel technique of measuring fungal biomass in infected tissue and.
2)a standard cut stem inoculating method which measures lesion length as criteria for virulence. This research will answer some fundamental questions on the biology of this pathogen as it pertains to six important crops grown in a region where Sclerotinia diseases commonly occur.


3.Progress Report

This project was initiated on June 1, 2008, research is ongoing, and the overall objective is to characterize the genetic variation and virulence of S. sclerotiorum on six crops in the North Central Region of the USA. ADODR monitoring activities to evaluate research progress included phone calls, meetings with the cooperator, and an annual meeting held each year in January.

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.


Last Modified: 4/20/2014
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