Sclerotinia sclerotioruna was isolated from decayed tips of carrot leaves at the harvest time, the middle of December, 1972. They seemed to be infected by ascospores in autumn. After then the plants were transplanted to upland and paddy fields for the purpose of seed production. Freshly shot leaves of these plants were infected by the disease in both fields. In experiment, carrot roots planted in soil mixed with diseased leaves were severely affected by S. sclerotiorum. Infection to roots was occurred when intact sclerotia with organic matter, cut sclerotia and mycelial mass (5 mm in diam.) were laid on the roots of plants or mycelial mass with organic substance laid within 1 cm from the roots. Mycelial growth was observed in autoclaved soil and compost within the depth of 5 mm, but not in the unautoclaved ones. And no infection to roots was occurred in raw compost mixed with sclerotia.
