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Title: Bioherbicidal effects of Myrothecium verrucaria on Glyphosate-resistant and -susceptible Palmer amaranth biotypes

item Hoagland, Robert
item Teaster, Neal
item Boyette, Clyde

Submitted to: Allelopathy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/29/2012
Publication Date: 3/29/2013
Citation: Hoagland, R.E., Teaster, N.D., Boyette, C.D. 2013. Bioherbicidal effects of Myrothecium verrucaria on Glyphosate-resistant and -susceptible Palmer amaranth biotypes. Allelopathy Journal. 31(2):367-376.

Interpretive Summary: Palmer amaranth, a serious problem of several crops (soybean, corn, and cotton) in the southern U.S., has recently evolved resistance to the herbicide glyphosate making it even more problematic. Scientists at the USDA-ARS, Crop Production Systems Research Unit, and the Biological Control of Pests Research Unit, Stoneville, MS studied the bioherbicidal effects of the fungal plant pathogen, Myrothecium verrucaria (MV) on Palmer amaranth in search of an alternative approach to control this serious weed. Whole plant and excised leaf bioassays of cloned greenhouse-grown plants, plus tissue from a mature, field-grown plant were tested for the bioherbicidal efficacy of MV mycelial preparations. Regardless of whether plants were resistant or susceptible to glyphosate, MV was equally phytotoxic to all plants tested (2-week-old, 4-week-old and mature), and injury increased with the MV mycelial concentration applied. MV disease progression was more rapid in young plants, with severe disease and 100% mortality noted about 30 hours after treatment, but in older plants a moderately severe disease rating was exhibited at 168 h after treatment. No significant differences were found in disease progression of glyphosate-susceptible and –resistant plants of the same age. Since MV can control both glyphosate-resistant and -susceptible Palmer amaranth plants under greenhouse conditions, this bioherbicide may be a viable candidate for its control. This is the first research using this bioherbicide to control both herbicide-susceptible and-resistant weeds of one species.

Technical Abstract: Bioherbicidal effects of the fungus Myrothecium verrucaria (MV) on glyphosate-resistant and -susceptible Palmer amaranth were examined on whole plants and in leaf bioassays of young and mature plants. Leaf bioassays using mycelia from the fermentation product of MV indicated that excised leaves of young greenhouse-grown (glyphosate resistant and -susceptible) and mature field-grown (glyphosate-resistant) plants were injured by the bioherbicide. Generally, injury was directly proportional to the MV mycelial concentration applied, and glyphosate-susceptible and -resistant plant leaves were equally sensitive to the MV phytotoxic effects as measured by reduction of chlorophyll content. Similar effects occurred on whole plants challenged by MV spray applications to foliage, as substantiated by plant growth reduction (fresh and dry weight accumulation) at termination of the time course. MV disease progression over a 7-day period in young (2-week-old) plants increased with time, and at 48 to 72 h after treatment, disease was severe with nearly 100% mortality occurring and there were no significant response differences in the glyphosate-susceptible and -resistant plants. As expected, disease progression in 4-week-old plants was slower, indicating more tolerance to the bioherbicide, but injury was moderately severe at the endpoint (168 h) after treatment. Results demonstrate that under greenhouse and laboratory conditions, MV can control both glyphosate-resistant and susceptible Palmer amaranth seedlings which could make this bioherbicide a possible candidate for use against this economically important weed.