Submitted to: Ecological Interactions and Biological Control
Publication Type: Book / Chapter
Publication Acceptance Date: June 20, 1997
Publication Date: N/A
Technical Abstract: Diseases caused by parasitic fungi may be used to control problem weed species when chemical herbicides are undesirable or uneconomical. For biocontrol of weeds in rangelands or wild areas, pathogens are chosen that can be released in a few sites to spread naturally over the range of the target weed. Rust fungi or other highly specialized parasites are often selected for this approach, because their host specificity eliminates any danger to other, desirable plant species. In natural associations of plants and rust fungi, there is often a complex array of host resistance genes and pathogen virulence genes that can overcome the resistance. A mathematical model of coevolution of gene-for-gene host-pathogen systems was used to simulate changes in levels of resistance in weed populations and virulence in biocontrol pathogen populations. Outcomes of simulations with the model predicted long-term success of biocontrol. Conditions for equilibrium of resistance and virulence in host and pathogen populations were identified. The effect of the pathogen host weed fitness was determined over the range of fluctuations in levels of host resistance and pathogen virulence found in model simulations. Simulation results showed that for successful biocontrol of weeds with rust fungi, it is not necessary that resistance be completely absent from the weed population or that an equilibrium be reached between resistance and virulence. What is essential to success is that the rust population released for biocontrol must contain virulence genes to match any resistance genes present in the weed population. When that is true, virulence in the pathogen adjusts to overcome changing resistance in the host weed.