Extending the shelf-life of Myrothecium verrucaria, a bioherbicide

Authors: Hoagland, Robert; Boyette, Clyde; Stetina, Kenneth - Ken

Submitted to: American Journal of Plant Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/25/2017
Publication Date: 11/29/2017
Citation: Hoagland, R.E., Boyette, C.D., Stetina, K.C. 2017. Extending the shelf-life of Myrothecium verrucaria, a bioherbicide. American Journal of Plant Sciences. 8:3272-3284.

Interpretive Summary: Weed control is a major concern globally, and weeds that are tolerant or resistant to herbicides present an even larger problem. Many microorganisms that cause diseases in weeds have been evaluated as bioherbicides for potential alternatives to herbicides. Since these bioherbicides are alive, stability and long-term storage are major factors for transitioning them into commercial products. Scientists in the USDA-ARS, Crop Production Systems Research Unit and the Biological Control of Pests Research Unit, Stoneville, MS developed and tested a method [freeze-drying followed by storage at -20 °C (-4 °F)] to improve the stability of the bioherbicide, Myrothecium verrucaria (MV strain IMI 368023). Bioassays (dark-grown and greenhouse-grown hemp sesbania seedlings) demonstrated that freeze-dried MV mycelia preparations stored at -20 °C for 8 years retained bioherbicidal activity. Although some activity was lost during this storage, the stored material still caused greater than 80% mortality, 15 days after treatment. Freeze-drying is a useful method to reduce the bulk and cumbersomeness of storing heavy liquid fermentation MV product. Since MV exhibits bioherbicidal activity on several weeds including: sicklepod, hemp sesbania, kudzu, redvine and glyphosate-resistant Palmer amaranth, these findings may increase its marketability and present the potential to use the dried material in soil treatments or in a more concentrated form.

Technical Abstract: The bioherbicidal efficacy of freshly fermented Myrothecium verrucaria IMI 368023 (MV) mycelia formulations and MV mycelia preparations that had been freeze-dried and then stored at -20 °C for 8 years were compared. Two concentrations of each formulation (1x and 0.5x) were tested, utilizing bioassays on seedlings of the weed, hemp sesbania (Sesbania exaltata) under greenhouse conditions or in in darkness utilizing hydroponically grown seedlings. Freeze drying of freshly prepared MV mycelium produced a light, brownish-colored powder. Tests on the efficacy of this reconstituted 8-yr-old dried material showed that some bioherbicidal activity was lost during long-term storage, i.e., ~20 % and ~ 60% seedling dry weight reduction at the 1x and 0,5x rate, respectively. Although plant mortality was greater in the fresh mycelial preparations treatments versus the freeze-dried and stored samples at all time points in the time-course, the stored material still caused > 80% mortality, 15 days after treatment. Comparative disease progression ratings also showed a similar trend. Overall results show that freeze-drying MV is a useful method to reduce the bulk and cumbersomeness of storing heavy liquid fermentation product, while retaining bioherbicidal activity. These findings increase the utility of this bioherbicide and offer the potential to use the dried material in soil treatments or in a more concentrated form than attainable via the fermented product.