First Report of Web Blight Caused by Thanatephorus cucumeris on Cupaniopsis anacardiopsis in the United States.. R. T. McMillanJr.,, University of Florida, Tropical Research and Education Center, Homestead, FL 33031. H. Vande Hei, and W. R. Graves, University of Florida, Tropical Research and Education Center, Homestead, FL 33031. Plant Dis. 78:03171. Accepted for publication 6 December 1993. Copyright 1994 The American Phytopathological Society. DOI: 10.1094/PD-78-0317B.
Cupaniopsis anacardiopsis (A. Rich) Radlk., commonly known as car-rotwood, is a popular subtropical landscape tree grown only in Dade County, Florida. Water-soaked leaf spots that increased rapidly in size and became light tan to brown necrotic areas were observed on carrotwood in commercial nurseries during periods of cloudy, rainy weather from July through September 1991 and 1992. Severe infections resulted in defoliation and death of plants. A Rhizoctonia-like fungus was isolated from infected leaves and stems on potato-dextrose agar and was identified as Thanatephorus cucumeris (A.B. Frank) Donk (anamorph of Rhizoctonia solani Kuhn). The identity of isolate IMI 354026 was verified as T. cucumeris by the International Mycological Institute, Kew, England. Eight-month-old plants of C. anacardiopsis were inoculated with hyphal suspensions of T. cucumeris, placed in a dew chamber at 27 C for 7 days, and observed for symptoms after 10 days. Foliar web blight symptoms on inoculated plants were identical in all respects to the blight resulting from natural infection. Tests were repeated several times with similar results. Koch’s postulates were fulfilled by reisolation of the pathogen. This appears to be the first occurrence of T. cucumeris on C. anacardiopsis in the United States.