Submitted to: Weed Science Society of America Meeting Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 5/8/2006
Publication Date: N/A
Interpretive Summary: As with other invasive weeds, the soilborne fungi Rhizoctonia, Fusarium and Pythium spp. was consistently isolated from roots damaged by root-feeding insects. The insect-damaged, fungi-infected plants are obvious by being stunted and yellow or reddened. Soil inhabiting, root-infecting fungi have been found in the roots of other perennial invasive weeds such as leafy spurge and spotted and diffuse knapweeds in previous studies. This dual effect has been shown to lead to early mortality of the damaged, diseased plants of these weed species. These facts allow the development of methods for the selection of new insect biocontrol agents based on whether they can damage roots to a degree that provide insect/plant pathogen dual effects or synergisms. Such methods can reduce costs and increase the effectiveness present and future biocontrol programs.
Technical Abstract: Isolation of fungi from insect-damaged roots of Lepidium draba in Switzerland, Hungary and Austria revealed that this species was often infected with one or more soilborne fungi. Plants with evident stunting and/or chlorosis and reddening of leaves nearly always exhibited root damage by one or more insects. In Switzerland, roots of L. draba damaged by one or more unknown insects were infected with Rhizoctonia solani and Fusarium spp. Surveys for L. draba plants with characteristic chlorosis and reddening in Hungary and Austria in 2004 and 2005 showed that such plants had root galls typical of weevils of Ceutorhynchus spp. The galls were often decayed at exit points of the insects and adjacent root tissue was consistently infected with Rhizoctonia solani, Fusarium and Pythium spp. A similar complex of soilborne fungi had been found in association with insect damage to roots of leafy spurge and spotted and diffuse knapweed and comparative virulence tests of such fungi showed that greater virulence was associated with isolates of this origin. The prevalence of such associations, especially in yet another instance involving a highly invasive herbaceous perennial weed may indicate that such highly destructive insect/pathogen combinations are a previously overlooked key to biological control success. A concept for utilizing a multitrophic approach to screening for new biocontrol agents of exotic, invasive herbaceous perennial weeds of rangelands will be discussed.