2010 Annual Report
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. 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. There is limited published information on the genetic variation of S. sclerotiorum isolates across the United States that includes information on isolate virulence across crops such as soybean, sunflower, canola, dry bean, field pea and lentil. Our first objective is to make a collection of isolates of the pathogen from these crops, identify mycelial compatibility groups (MCG’s), use microsatellite markers to characterize the genetic variation and then characterize virulence of isolates that have common and unique haplotypes on six crops grown in the North Central Region. We completed screening on 149 isolates which form 46 MCGs. A few MCGs appear to be quite common although most are relatively rare and represented by 1-2 isolates: four MCGs contain 10 or more isolates while 36 MCGs contain a single isolate. To date, no differences in MCGs have been detected across crops. The most common was MCG 9 found in nine states and on all four crops. Six of the most common MCGs represented 58% of the isolates and were found across crops. The frequency at which MCG’s occur varies with crop and geographic region. We also tested a selection of 30 isolates for virulence on the six crops in the greenhouse; these isolates represented the diversity of isolates across crops and geographic areas of the collection. The entire experiment consisted of 900 five week-old plants inoculated with the cut-stem/straw technique, and seventy two hours after inoculation all lesions were measured with electronic calipers. Analyses are ongoing, but there are obvious differences between isolates, and a repeat of the experiment is currently in progress. We have also been measuring growth rates of isolates at different temperatures to determine if there are differences among isolates in the adaptation to environmental conditions. 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. Understanding the genetic variation and virulence of the current isolates of S. sclerotiorum in the United States is a fundamental part of the overall strategy of using resistance or other controls for this pathogen.