EUCLEG: Identifying sources of resistance to clover rot in red clover

In temperate and Nordic regions of Europe Sclerotinia trifoliorum Erikks. causes clover rot in red clover (Trifolium pratense L.). The fungus attacks the plants during the winter and can destroy entire fields by early spring. Fungicide applica-tions are too costly for forage crops, and breeding resistant varieties progresses slowly due to the outcrossing nature of red clover and because little or no sources of resistance are known. Furthermore, very little is known about the genomic control of Sclerotinia in red clover.
We have investigated the variation available for clover rot susceptibility in a highly diverse collection of 396 diploid red clover accessions, most of them from Europe. The collection consists of ecotypes, landraces, cultivars and recent breeding mate-rial. This study was performed in the framework of the EUCLEG project (http://www.eucleg.eu/), which aims to reduce Europe's and China's dependency on protein imports by developing efficient breeding strategies for five legume crops, including red clover.
All 396 accessions were screened using a plant-based bio-test in controlled condi-tions. The same S. trifoliorum isolate derived from a single spore from an aggres-sive isolate (identified and characterized in a previous study) was used in all trials. Each accession was inoculated and evaluated three times, and the disease severity index (DSI) was determined for each accession.
Red clover accessions differed significantly in susceptibility. As expected, each accession comprised genotypes with different resistance levels. Accessions were identified that can be used as sources to further increase clover rot resistance by breeding. Future research within the EUCLEG project will identify molecular mark-ers for Sclerotinia resistance in red clover using Next Generation approaches.