Submitted to: American Phytopathological Society
Publication Type: Abstract Only
Publication Acceptance Date: April 7, 2004
Publication Date: August 1, 2005
Citation: Phytopathology 95:S156 Technical Abstract: Wilting and death of noninoculated (healthy) Russian knapweed (RK, Acroptilon repens) have occurred in recent greenhouse experiments at the USDA containment facility in Frederick, MD. Investigations were initiated to identify the pathogen, its source, and mode of dissemination in the greenhouse. A Phoma sp. pathogenic to RK was isolated from diseased plants, and DNA analyses confirmed that the pathogen was P. exigua. It may be that the current infections originated from remnants of Isolate 02-059 from Turkey, evaluated recently for biological control. Abundant pycnidia on diseased plants are most likely the source of inoculum. The fungus gnat (FG, Bradysia coprophila) and the shore fly (SF, Scatella stagnalis) may be involved in transmission of P. exigua. The fungus was easily isolated from adults and larvae of both insect species (47%, n = 147), unless they were surface disinfested with bleach (20% for 10 min.). Conidia were observed clearly on insect wings, and a preliminary study involving caged insects (n = 248 insects of both species) resulted in diseased plants, except in the "no insect" control cage.