Submitted to: Journal of Plant Diseases and Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 1, 2004
Publication Date: March 4, 2004
Citation: Quimby Jr, P.C., Gras, S., Widmer, T.L., Meikle, W.G., Sands, D. 2004. Formulation of sclerotinia sclerotiorum for use against cirsium arvense. Journal of Plant Diseases and Protection. Special Issue XIX:491-495
Interpretive Summary: Canada thistle is a highly aggressive weed from Southeastern Asia that has invaded most of the United States. This rhizomatous perennial spreads vegetatively and by seed; thus, the weed is extremely difficult to control and has been named by the United States Department of Agriculture as one of its top targets for biological control. One candidate biological control agent that has been proposed in the past for use in the manipulative sense is a cosmopolitan fungus with a broad host range. The purpose of this research was to determine the best method for growing this fungus and to find an effective technique for storing it with a long shelf-life without losing its ability to infect Canada thistle. A liquid broth produced from potatoes and sugar was determined to give the best results for growth. When sugar was added to the fungus before harvest and combined with a gelatin to form granules when dried, the fungus was still active after 40 days in a freezer. The primary benefit of this research is that it demonstrates that a method can be developed for producing a long shelf-life of this fungus. This is important for a company that might be interested in producing this fungus as a biocontrol agent and to agencies and farmers who are interested in a biological approach to control of this weed.
Cirsium arvense (L.) Scop. (Canada thistle) is a highly aggressive weed from Southeastern Asia that has invaded most of the United States. This rhizomatous perennial spreads vegetatively and by seed; thus, the weed is extremely difficult to control and has been named by the United States Department of Agriculture as one of its top targets for biological control. One candidate biological control agent that has been proposed in the past for use in the manipulative sense is a cosmopolitan fungus with a broad host range, viz., Sclerotinia sclerotiorum (Lib.) de Bary. A limitation for the manipulative use of S. sclerotiorum is the difficult task of stabilizing, formulating, and applying mycelia as a mycoherbicidal product to the weeds. Although sclerotia are easily produced, their use is too problematic because of their innate dormancy. In this study, various substrates for production, viz., quinoa seeds, sunflower seeds, and potato dextrose broth (PDB) were compared; PDB gave the best results, but necessitated additional steps for stabilization. After 3 days growth in Erlenmeyer flasks, osmotic shock was produced by adding sucrose at 25% w/v 24 h before harvest. The fermentation product was harvested and stabilized by adding 1% w/v sodium alginate and dripping the suspension into 0.2 M calcium chloride to form calcium alginate/fungal mycelia granules. The granules were then sieved and dried for 30 min at 45° C with a fluid-bed-dryer (FBD) and followed by drying in a chemical fume hood for 72 hours until the water content was generally lower than 9%. After 40 days storage at -20°C over silica gel, individual dried granules were placed on potato-dextrose-agar in petri dishes at 10 granules per plate or on leaf discs at 1 granule per disc (4 discs per experimental unit) in a high humidity environment. One-hundred per cent of the rehydrated granules produced fungal colonies in the petri dishes after 2 to 3 days. Necrosis appeared after 2 days and was complete after 4 to 5 days in the leaf discs treated with fungal-impregnated granules. Osmotic shock, followed by dehydration, predisposed the fungus, encapsulated in calcium alginate, to withstand long-term storage under freezing conditions while remaining viable upon rehydration and pathogenic to tissue of C. arvense.