Effects of Myrothecium verrucaria on two glyphosate-resistant Amaranthus palmeri biotypes differing in Betacyanin content

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

Submitted to: American Journal of Plant Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/18/2020
Publication Date: 2/21/2020
Citation: Hoagland, R.E., Boyette, C.D., Jordan, R.H., Stetina, K.C. 2020. Effects of Myrothecium verrucaria on two glyphosate-resistant Amaranthus palmeri biotypes differing in Betacyanin content. American Journal of Plant Sciences. 11:214-225.
DOI: https://doi.org/10.4236/ajps.2020.112017

Interpretive Summary: Palmer amaranth is an economically important and aggressive weed that has developed resistance to several herbicides, including glyphosate. Methods for controlling this weed include alternative herbicides and herbicide mixtures. Bioherbicidal control of this weed with plant pathogens has also been studied. Scientists from the Crop Production Systems Reseach Unit and the Biological Control of Pests Research Unit, at Stoneville, MS previously demonstrated that the bioherbicidal fungus, Myrothecium verrucaria (MV) has potential for controlling several weeds, including Palmer amaranth. During field surveys for herbicide-resistant weeds, a biotype of Palmer amaranth was found in a population of red-pigmented plants that was void of the red pigment. Further examination showed that both red and green biotypes were resistant to glyphosate. Greenhouse studies were conducted to determine the efficacy of MV on these biotypes. Results indicated that MV was effective on both biotypes, but effects on growth reduction, injury and control were more rapid and generally greater in the green biotype, suggesting that compounds resonsible for red pigmentation may act as defense against pathogen attack.

Technical Abstract: Previously we found two biotypes of Amaranthus palmeri (Palmer amaranth) in a population of this economically important weed that were resistant to glyphosate but differed with respect to pigmentation. One biotype was typically red-pigmented (betacyanin) while the other was green, with no visual appearance of red hue on any plant part at any growth stage. We have also reported that a strain of Myrothecium verrucaria (MV) exhibited bioherbicidal activity against several important weeds including glyphosate-resistant Palmer amaranth. In greenhouse tests, MV was applied to these two biotypes (red and green) at two ages (3-week- and 6-week-old) and effects monitored over a 5-day time course. Initial symptoms of MV (16 to 24 hours after inoculation) were: epanasty, wilting and development of lesions on leaves and stems. Generally, the younger plants tended to be more sensitive to MV than older plants. Bioherbicidal damage increased with time leading to necrosis and plant mortality and increasing disease progress. Severe loss of fresh weight occurred in both biotypes as compared to untreated plants. Results indicated that MV was effective on both biotypes, but effects on growth reduction and disease progression were more rapid and generally greater in the green biotype, suggesting that compounds resonsible for red pigmentation may act as defense against pathogen attack.