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Title: The impact of temperature on the production and fitness of microscleotia of the fungal bioherbicide Mycoleptodiscus terrestris

item Jackson, Mark
item Dunlap, Christopher
item Sherer, Judy - Us Army Corp Of Engineers (USACE)
item Heilman, Mark - Sepro Corporation
item Palmquist, Debra

Submitted to: Biocontrol Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/31/2011
Publication Date: 1/31/2011
Publication URL:
Citation: Jackson, M.A., Dunlap, C.A., Sherer, J.F., Heilman, M.A., Palmquist, D.E. 2011. The impact of temperature on the production and fitness of microscleotia of the fungal bioherbicide Mycoleptodiscus terrestris. Biocontrol Science and Technology. 21(5):547-562. DOI: 10.1080/09583157.2011.564728

Interpretive Summary: The plant pathogenic fungus Mycoleptodiscus terrestris (MT) is a natural enemy of hydrilla (Hydrilla verticillata) and is being developed as a biological control agent for this invasive aquatic weed. Temperature is an environmental factor that must be optimized for both the production and use of MT. Using deep-tank fermentation, cultures of MT grown at 24 C (75 F) had optimal yields and produced a form of MT that survived air-drying and had good shelf-life when stored at refrigerated temperatures. Since the water temperatures present in hydrilla infestations can vary widely depending on the time of year and level of hydrilla growth, we examined the temperature limitation for the growth of air-dried MT formulations after rehydration and incubation on water agar at various temperatures. Rehydrated MT preparations grew at temperatures of 20-34 C (68-93 F) but optimal growth occurred at temperatures of 24-28 C (75-82 F). These studies suggested that applying MT to hydrilla when water temperatures are 75-82 F may improve the effectiveness of MT in controlling hydrilla.

Technical Abstract: The plant pathogenic fungus Mycoleptodiscus terrestris is being developed as a bioherbicide for the invasive aquatic weed hydrilla (Hydrilla verticillata). We evaluated the impact of temperature on the growth and stability of M. terrestris cultures during liquid culture fermentation and on the viability and conidia production potential of air-dried microsclerotial preparations. After 4 days culture growth in a rotary shaker incubator at various temperatures (20-36 C), growth at 24-30 C produced significantly higher biomass accumulations and microsclerotia concentrations while temperatures of 22-24 C resulted in a significantly higher colony forming units (cfu). Cultures of M. terrestris did not grow at 36 C. Cultures of M. terrestris grown at differing temperatures were air-dried and stored at 4 C. After 1 month storage, no significant difference in viability for air-dried microsclerotial preparations from cultures grown at 24-32 C (> 88% germination) and after 5 months storage over 85% germination was seen in cultures grown at 24-30 C. Air-dried microsclerotial preparations from cultures grown at 20-24 C showed increased conidia production over 5 months storage while those grown at 26-36 ºC showed conidia production peaking after 1-3 months storage. Air-dried microsclerotial preparations of M. terrestris were incubated on water agar at temperatures ranging from 20 C to 36 C. Incubation at temperatures of 24-28 C resulted in optimal hyphal and sporogenic germination. Air-dried microsclerotial preparations did not germinate hyphally at 36 C or sporogenically at 20, 32, 34, or 36 C. These data suggest that the application of air-dried M. terrestris preparations when water temperatures exceed 32 C may result in limited hyphal germination and conidia production potentially reducing their efficacy in infecting and controlling hydrilla.