Submitted to: Biocontrol
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/27/2000
Publication Date: 4/1/2002
Citation: Caesar, A.J., Campobasso, G., Terragitti, G. 2002. Identification, pathogenicity and comparative virulence of Fusarium spp. associated with insect-damaged, diseased Centaurea spp. in Europe. Biocontrol. 47(2):217-229. Interpretive Summary: Spotted and diffuse knapweed, respectively, are, highly invasive weeds of foreign origin that have, along with Russian knapweed, infested an estimated 4.8 million hectares of rangeland in the western United States and Canada. Knapweed species are capable of causing fatal brain and nerve damage to livestock and reductions in grazing capacity of infested land. Interactions of insects applied for biological control with soilborne plant pathogens are what cause stand reductions in other weeds, such as leafy spurge. The improvement of the frequency of successful impact upon release of the insects may depend on assuring the presence of plant pathogens. knapweeds in Eurasia occur as widely scattered and sparse, often diseased, stunted plants and are usually infested with one or more insects in their roots and crowns. Fungi of one species commonly found in association with insect damaged plants were identified and tested on plants of knapweed for the level of disease they cause. Three species were identified causing significant levels of disease. Knowing that pathogenic fungi are associated with damage caused by root attacking insects in the native range of the weeds, where they are under natural control should indicate that this pathogen component is needed for successful biocontrol in North America. Along with findings from earlier studies, biocontrol personneland private and public land managers are alerted to the need for biocontrol that accounts for and includes plant pathogens as synergists.
Technical Abstract: Identification, pathogenicity and comparative virulence of Fusarium spp. associated with diseased Centaurea spp. in Europe. BioControl 45: Fusarium spp. isolated from insect-infested, diseased Centaurea diffusa and Centaurea maculosa in Europe were assessed for pathogenicity to North Ameri iplants of their respective original hosts: either C. diffusa or C. maculos Of the ten isolates of Fusarium spp. isolated from diseased Centaurea spp. the Caucasus region of Russia and eastern Europe, all caused one or more disease symptoms or reductions in fresh weight of North American accessions their original host species. In three instances, these reductions were statistically significant (P=0.05). Symptoms included overall stunting, roo lesions, and crown rot. Reductions in fresh weight of C. diffusa ranged fro 17-78%, and C. maculosa exhibited reductions of 18-82%. The pathogenic cultures were identified as F. solani, F. tricinctum and F. oxysporum. Six seven other cultures were identified as F. oxysporum, and one as F. tricinctum. It was concluded that further screening of a larger set of isolates of foreign Fusarium spp. under quarantine conditions stateside or limited USDA-ARS overseas facilities is justified and promising. Key Words: soilborne pathogens, rangeland weeds, Asteraceae, synergism