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

R. E. Hoagland, N. D. Teaster, C. D. Boyette
Allelopathy journal 2013 v.31 no.2 pp. 367-376
Amaranthus palmeri, Myrothecium verrucaria, allelopathy, bioassays, biopesticides, biotypes, chlorophyll, disease course, dry matter accumulation, fermentation, fungi, glyphosate, greenhouses, growth retardation, herbicidal properties, herbicide resistance, leaves, mature plants, mortality, mycelium, phytotoxicity, plant growth, seedlings, weed control, weeds
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 greenhousegrown (glyphosate resistant and -susceptible) and mature field-grown (glyphosateresistant) 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-d 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.