Unique Symptoms on Stored Carrots and White Mold on Hairy Vetch Caused by Sclerotinia sclerotiorum in Finland. H. Koponen, Department of Plant Biology, P.O.Box 27. J. P. T. Valkonen, Department of Plant Production, P.O.Box 27, FIN-00014 University of Helsinki, Finland. Plant Dis. 80:599. Accepted for publication 8 March 1996. Copyright 1996 The American Phytopathological Society. DOI: 10.1094/PD-80-0599D.
Symptoms including round and deep cavities on tap roots after 1 month of storage followed by entire softening of the tap roots occurred in carrots (Daucus carota L.) on a few farms in Finland in 1992 to 1994 and caused substantial economic losses. Sclerotinia sclerotiorum (Lib.) de Bary was isolated from the diseased carrot tap roots. White mold (S. sclerotiorum) is known as a storage disease of carrots in Finland and other countries, but white, cottony mycelium characteristic to S. sclerotiorum was not visible on the diseased carrot tap roots under the storage conditions of this study (0.5°C; relative humidity = 100%). The unusual cavity symptoms may have been associated with the storage of carrots by enclosure into large plastic bags (approximately 1 m3). Healthy, surface-sterilized whole tap roots of the carrot cvs. Napoli and Panther were experimentally inoculated with S. sclerotiorum isolated from the carrots showing cavity symptoms and were incubated in plastic bags under the above storage conditions. Cavity symptoms identical to those described above were observed and S. sclerotiorum was reisolated from the the inoculated, diseased tap roots. In all fields from which the carrots developing the unique tap root cavity symptoms were harvested, hairy vetch (Vicia villosa Roth) had been grown as the immediate pre-crop. Examination of the densely and vigorously growing stands of hairy vetch revealed white mold and an abundance of sclerotia of 5. sclerotiorum on basal stems and leaves. These results provided circumstantial evidence for increased risks to the development of the S. sclerotiorum-associated storage disease in carrots if hairy vetch precedes carrot in crop rotation.