Stem Blight of Eustoma grandiflorum Caused by Sclerotium rolfsii

During a 4-week period in May through June 1996, 15% of 50 mature lisianthus (Eustoma grandiflorum) 'Maurine Blue' and 'Maurine White' plants exhibited stem blight in a landscape planting in west-central Florida. Initial disease symptoms included stem necrosis at the soil line, and yellowing and tan discoloration of leaves. As blighting of the stem progressed, infected plants wilted and died. Symptomatic stem sections from three plants were surface-disinfested in 0.5% NaOCl and placed on acidified 25% potato dextrose agar (APDA). Sclerotium rolfsii Sacc. was isolated from all three diseased stems. Pathogenicity of each of three S. rolfsii isolates was confirmed using two lisianthus 'Flamenco Blue' plants grown in 10.2-cm-diameter plastic pots containing a peat-based medium. Sclerotia produced on APDA were sprinkled on the soil surface around each plant base; 50, 100, and 5 sclerotia from isolates A, B, and C, respectively, were used (isolate C grew more slowly and produced fewer sclerotia than either A or B). Two noninoculated lisianthus served as controls. Plants were maintained in a greenhouse at minimum and maximum temperatures of ≈24 and 35°C, respectively. Plants inoculated with sclerotia from isolates A and B developed blight symptoms within 6 days. One of two plants inoculated with isolate C developed blight symptoms within 17 days, and the other remained symptomless, as did the control plants. Infection by S. rolfsii was confirmed by reisolation from symptomatic tissue. This is the first report of stem blight of lisianthus caused by S. rolfsii.