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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

2011 Annual Report


1a.Objectives (from AD-416)
1. Determine genetic variation of S. sclerotiorum from crops grown outside the North Central region using DNA fingerprinting and mycelial compatibility groups. 2. Characterize the virulence of selected isolates on cultivars of soybean, sunflower, canola, dry bean, pea and lentil. 3. Prepare a set of isolates representing the genetic and virulence diversity of S. sclerotiorum in the United States for distribution to researchers on Sclerotinia.


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. In a project currently funded by the Sclerotinia initiative, 146 isolates of the pathogen from the North Central USA were characterized using mycelia compatibility groups (MCG’s) and DNA fingerprinting. We are currently evaluating the virulence of those isolates on 6 crops grown in the region. We identified 43 MCG’s and the DNA fingerprints of the isolates were strongly associated with MCG’s. This new information on the biology of S. sclerotiorum in the North Central Region has indicated that specific biotypes of the fungus can be widespread within the region and occur on multiple crops. MCG 9, for example is found on sunflower, soybean, dry bean and canola over nine widely separated states. Although we now have good information on the population of the pathogen in the North Central region, we need additional information on the population from the rest of the United States. It is clear from our research that biotypes of the pathogen can be disseminated over large distances. Isolates that occur in areas outside of the North Central area could impact crops and disease management in our region. Knowledge of the genetic variation and virulence of isolates of S. sclerotiorum in the United States is fundamental information needed for understanding the biology of this pathogen. Such information will help us with our overall strategy of using resistance or other controls for this pathogen. It may help explain the mixed results of field screening for resistance that has been observed over the country and the lack of correlation between field and laboratory evaluations. Furthermore, sensitivity of the pathogen to fungicides or other chemicals can be evaluated with greater reliance when there is a population of the pathogen that has been characterized with MCG’s, DNA fingerprinting and virulence traits. The currently funded project which focused on the North Central Region and this new project will establish a collection of isolates that represents the variation of the pathogen in the United States. It will become a benchmark of the pathogen population in the United States. This collection will be made available to researchers working on all aspects of the biology and control of S. sclerotiorum. This research will collect isolates of S. sclerotiorum from various crops grown in areas outside of the North Central region. The mycelial compatibility groups will be identified and microsatellites will be used to characterize the genetic variation. Then, isolates representative of the clones/genetic groups, will be characterized for virulence on six crops (soybean, sunflower, canola, dry bean, pea and lentil) using a standard cut stem inoculating method which measures lesion length as criteria for virulence. A set of isolates representing the genetic and virulence diversity of S. sclerotiorum in the United States will be prepared for distribution to Sclerotinia researchers.


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.

Sclerotinia sclerotiorum is one of the most important pathogens of field crops in the USA. This project examines genetic variation and virulence of isolates on crops grown in areas outside of North Central Region. Plant pathologists and plant scientists in states outside of the North Central Region were contacted for isolates of S. sclerotiorum. Some western statecollaborators had been contacted earlier and isolates were obtained to use with the previous study of isolates in the North Central Region. We obtained 55 isolates from 11 states (WA, CA, OR, SC, NC, AR, ID, OK, FL, GA, AR) outside of the North Central Region. Many of those contacted did not have isolates of the pathogen, and a few are still trying to obtain isolates for this project. The isolates obtained were from a variety of crops, both field and vegetable. DNA has been extracted and we are now in the process of doing the molecular studies to determine the microsatellite patterns. MycelialCompatibility Group (MGC) evaluations are still in progress and all MCG’s of these isolates are being compared to MCG’s identified in the previous project. In the Fall of 2011, we will begin the pathogenicity testing in controlled environment facilities.


Last Modified: 7/25/2014
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