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First U.S. Report of Pseudocercospora paederiae Leaf Spot on the Invasive Exotic Paederia foetida

Paederia foetida L., commonly referred to as skunk vine, is a native of eastern and southern Asia and was introduced into the United States prior to 1897. By 1916 it was already a troublesome weed in central Florida. It is a fast growing perennial twining vine (up to 7 m) with a woody rootstock adapted to a wide range of light, soil, water, and salt conditions (4). Naturalized in Florida, Georgia, Hawaii, Louisiana, North Carolina, South Carolina, and Texas, it occurs most often in disturbed areas. In Florida, where it is listed by the Florida Department of Agriculture and Consumer Services as a noxious weed, it invades various native plant communities including sandhills, flood plains, and upland mixed forests, where it creates dense canopies leading to injury or death of native vegetation and structural alteration of the native plant community (2,4). Current work underway to find biological control agents for invasive weeds led to the discovery in central Florida of a skunk vine plant with irregular to angular, sunken leaf spots ranging in color from shiny black to dark brown, some with tan centers and dark brown borders. Leaf spots had coalesced in some areas, blighting portions of leaves. Pseudocercospora paederiae (Sawada ex) Goh & Hsieh (1,3) was recovered from these leaf spots. Fruiting was amphigenous (chiefly epiphyllous) with globular or subglobular stromata, formed singly or coalesced, 37.2 μm wide (range = 19.9 to 62.3 μm). Conidia were hyaline to faintly olivaceous, with up to 6 septa, straight to mildly curved, measuring 49.6 μm (range = 18.8 to 72.3 μm) × 4 μm (range = 3 to 5 μm). To confirm Koch's postulates, a healthy, vigorous P. foetida plant in a 12 liter pot was spray-inoculated with 47 ml of a conidial suspension (13,000/ml) of P. paederiae. The plant was covered with a clear plastic bag to create a moist atmosphere and kept at room temperature (25°C) for 3 days after which it was uncovered and moved into a greenhouse. The greenhouse temperature fluctuated between 15°C (nighttime) and 29°C (daytime). Symptoms started appearing after 2 weeks, becoming more prominent by the third and fourth week. The inoculated plant showed irregular to angular dark brown to black leaf spots with dark brown borders. Necrosis along veins was observed and severely infected leaves abscised. The fungus was consistently recovered from inoculated symptomatic leaf tissue. Continued incubation of the plant under greenhouse and outdoor raised bench conditions eventually resulted in the secondary infection and leaf spotting of new foliage. P. paederiae was recovered from these secondary lesions. P. paederiae has been previously reported from Taiwan, China, and Japan. This represents the first report of the pathogen in the Western Hemisphere. Pathogenicity tests suggest possible application as a mycoherbicide.

References: (1) C. Chupp. 1953. A Monograph of the Fungus Genus Cercospora. Cornell University Press. Ithaca, New York. (2) G. Gann and D. Gordon. Natural Areas J. 18:169, 1998. (3) W. H. Hsieh and T. K. Goh. 1990. Cercospora and Similar Fungi from Taiwan. Maw Chang Book, Taiwan, Republic of China. (4) K. A. Langeland and K. C. Burks, eds. 1998. Identification & Biology of Non-Native Plants in Florida's Natural Areas. University of Florida Press, Gainesville, FL.