Susceptibility of wild carrot (Daucus carota ssp. carota) to Sclerotinia sclerotiorum B. D. Jensen & M. R. Finckh & L. Munk & T. P. Hauser Received: 11 July 2007 / Accepted: 3 March 2008 # KNPV 2008 Abstract Sclerotinia soft rot, caused by Sclerotinia sclerotiorum, is a severe disease of cultivated carrots (Daucus carota ssp. sativus) in storage. It is not known whether Sclerotinia soft rot also affects wild carrots (D. carota ssp. carota), which hybridise and exchange genes, among them resistance genes, with the culti- vated carrot. We investigated the susceptibility of wild carrots to S. sclerotiorum isolates from cultivated carrot under controlled and outdoor conditions. Inoculated roots from both wild and cultivated plants produced sclerotia and soft rot in a growth chamber test. Two isolates differed significantly in the ability to produce lesions and sclerotia on roots of both wild carrots and cv. Bolero. Flowering stems of wild carrots produced dry, pale lesions after inoculation with the pathogen, and above-ground plant weight was significantly reduced 4 weeks after inoculation in a greenhouse test. Wild and cultivar rosette plants died earlier and fewer plants survived when inocu- lated with the pathogen under outdoor test conditions. Cultivar plants died earlier than wild plants, but survived as frequently. Plants inoculated in the crown died earlier and at a lower frequency than plants inoculated on leaves. Wild carrots may thus serve as a host of S. sclerotiorum and thus eventually benefit from any uptake of resistance genes, among them transgenes, via introgression from cultivated carrots. Keywords Pathogenicity . Risk assessment . Genetically modified crops . Wild plant–pathogen interactions Introduction The cultivated carrot (Daucus carota ssp. sativus) has wild relatives belonging to the same species, among which the wild carrot D. carota ssp. carota is commonly found, for instance, along road verges in temperate regions (Brandenburg 1981; Holm et al. 1997), including Denmark (Hansen 1981). It is a common and sometimes serious weed (Mitich 1996; Eur J Plant Pathol DOI 10.1007/s10658-008-9300-7 B. D. Jensen (*) : L. Munk Department of Plant Biology, Faculty of Life Sciences, University of Copenhagen, Thorvaldsensvej 40, 1871 Frederiksberg C, Denmark e-mail: dahl@life.ku.dk B. D. Jensen Department of Agricultural Sciences, Faculty of Life Sciences, University of Copenhagen, Thorvaldsensvej 40, 1871 Frederiksberg C, Denmark M. R. Finckh Faculty of Organic Agricultural Sciences, University of Kassel, 37213 Witzenhausen, Germany T. P. Hauser Department of Ecology, Faculty of Life Sciences, University of Copenhagen, Thorvaldsensvej 40, 1871 Frederiksberg C, Denmark