Submitted to: World Mycotoxin Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/16/2008
Publication Date: 3/3/2009
Citation: Weaver, M.A., Hoagland, R.E., Boyette, C.D., Zablotowicz, R.M. 2009. Macrocyclic Trichothecene Production and Sporulation by a Biological Control Strain of Myrothecium verrucaria is Regulated by Cultural Conditions. World Mycotoxin Journal 2(1):35-43. Interpretive Summary: Myrothecium verrucaria is a fungus that causes disease and or death of several invasive weed species and is currently being evaluated for use as a biological control agent of these weeds such as kudzu. However, the fungus also produces mycotoxins that may pose safety and environmental concerns for use of this biological control agent. This study explored how altering the growth conditions could enable spore production by this fungus without production of the mycotoxins. The maximum spore production occurred on potato dextrose agar, but this media also enabled high levels of mycotoxin production. Altering carbon and nitrogen sources was effective in reducing the mycotoxin levels while still supporting sporuation. These observations will allow the development of safer formulations of this biological control agent.
Technical Abstract: Myrothecium verrucaria is a pathogen of several invasive weed species and is currently being evaluated for use as a bioherbicide. However, the fungus also produces macrocyclic trichothecene mycotoxins such as verucarins and roridins. The safety of this biological control agent would be improved if an inoculum could be produced without concomitant accumulation of trichothecenes. Sporulation and trichothecene production by M. verrucaria was evaluated on standard potato dextrose agar (PDA) and a series of defined media. Sporulation was supported on PDA and on agar media with nitrogen present in the nitrate form, but not on media with nitrogen only available as ammonium. Production of verucarin A ranged from 380 to 684µg plate-1 on PDA. Verrucarin A levels were over 1000 µg plate-1 after 15 days growth on a defined citrate and sucrose media with ammonium sulfate, but were below the detection limit with ammonium nitrate amended media. Cultures grown on molasses-ammended media produced more verracurin A compared to glucose or sucrose-based substrates. Roridin A was consistently observed on PDA, but frequently undetectable on defined substrates. Results support the hypothesis that accumulation of macrocyclic trichothecens by this fungus can be altered by manipulating carbon and nitrogen sources. Furthermore, the production of these mycotoxins can be uncoupled from sporulation, suggesting that the bioherbicide can be readily produced on solid substrates while simultaneously yielding conidia that are less threatening to worker safety.