Phytophthora parasitica wilt of new cultivars of Catharanthus roseus

Robert T. McMillan,Jr., Joe F. Garofalo

Abstract


An outbreak of a stem and root rot on hybrid periwinkle (Catharanthus roseus (L.) G. Don) was observed in a nursery in Dade County, Florida. The Catharanthus hybrids infected with Phytophthora parasitica showed darkening of the tissues at the soil line followed by wilting of the stem. The lesions on the roots increased rapidly in size and became light to dark brown necrotic areas. A Phytophthora-like fungus was isolated from stems and roots on corn meal agar subcultured on potato-dextrose agar and identified as Phytophthora parasitica. The disease symptoms appeared as wilting of the leaves, roots were water soaked, turning to a brown to black color and the cortex sloughed easily from the stele. All of the periwinkle hybrids were susceptible to P. parasitica while the native white C. roseus was resistant. All chemicals applied provided significantly less number of P. parasitica infected plants than the untreated check (Table 2). Fosetyl-aluminum at 5 lb and etridiazole + thiophanate-methyl at 12.0 oz and metalaxyl-M at 1.00 fl oz were significantly better than). Fosetyl-aluminum at 1.0 lb, etridiazole + thiophanate-methyl at 6.0 oz, metalaxyl-M at 0.50 oz.

Keywords


phytophthora parasitica; fungicides; hybrid; resistance

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