First Report of Web Blight Caused by Rhizoctonia solani on Catharanthus roseus in Louisiana

Plant Disease
G E Holcomb, D E Carling

Abstract

Web (aerial) blight was observed in field plots of Catharanthus roseus (L.) G. Don (Madagascar periwinkle) during three consecutive summers at the Burden Research Center in Baton Rouge. Leaf spots formed first, followed by a general blighting of leaves and stems that resulted in circular areas of dead plants in the plots. Dead leaves were matted together but remained attached to plants. Mycelia, and occasionally small, brown sclerotia (1 to 3 mm) were observed on blighted foliage. During the first year, only prostrate-growing cultivars belonging to the Mediterranean series of C. roseus were infected, but in 2001 and 2002 upright-growing cultivars as well as those with prostrate growth habit became infected. The disease occurred in July and August during periods of hot, humid, and rainy weather. Among 52 cultivars in the 2001 trial, only 'Tropicana Pink', 'Tropicana Rose' and 'Stardust Orchid' were disease free. A Rhizoctonia sp. was consistently isolated from diseased plants and further characterized as R. solani Kühn AG-1 based on its multinucleate cells and hyphal anastomosis with several AG-1 tester isolates. On potato dextrose agar, colonies displayed morphologies with characteristics of AG-1 IA and AG-1 IB, therefore, iden...Continue Reading

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