Sclerotium rolfsii southern blight on brassidium hybrid orchid

Tara B. Pratt, Robert T. McMillan, Jr.


Brassidium hybrid orchid leaves were sent to the University of Florida, Plant Disease clinic in the Summer of 2002. Symptoms on leaves were a spreading, cottony, white mass of mycelium with necrotic centers 3-5 ×5-9 mm. Approximately 1% of leaves submitted were affected. Sclerotium rolfsii Sacc. was isolated from the affected leaves using acid potato dextrose agar (APDA). Two plastic boxes were lined with wet paper towels and six uninoculated leaves were placed in each. Three leaves in each box were treated as controls and received a 3 mm square of APDA, while the other three leaves in each box received a 3 mm of APDA, while the other three leaves in each box received 3 mm of S. rolfsii culture on APDA. All leaves were misted with water and enclosed to maintain humidity. Twenty-four hours later, infection was visible on two treated leaves. Within 72 hours, significant infection was visible on three of the six inoculated leaves. All control leaves remained uninfected. Sclerotium rolfsii was consistently reisolated from the inoculated leaves.


fan-shaped mycelium; orchid disease; sclerotia

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Proc. Fla. State Hort. Soc.     ISSN 0886-7283