Location: Soybean and Nitrogen Fixation ResearchTitle: Changes in herbicide sensitivity and competitive ability of Abutilon theophrasti over 28 years: implications for hormesis and weed evolution
|ETHRIDGE, SANDRA - North Carolina State University|
|CHANDRA, SAKET - North Carolina State University|
|EVERMAN, WESLEY - North Carolina State University|
|JORDAN, DAVID - North Carolina State University|
|OWEN, MICHAEL - Iowa State University|
|LEON, RAMON - North Carolina State University|
Submitted to: Pest Management Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/5/2023
Publication Date: N/A
Interpretive Summary: The ability of weeds to outcompete crop plants and proliferate depends on characteristics like size, leaf area, and growth rate. Weeds can also become more competitive by developing resistance to common herbicides. In this study, we examined how the competitive ability of A. theophrasti, commonly called velvetleaf, changed across a 28-year timespan using seeds collected from the same field in five years from 1988 to 2016. When single plants were grown far apart to eliminate competition, there were no differences in plant size measures, number of flowers, number of pods, or number of seeds. When velvetleaf plants from each collection year were grown together in a pot to create a monoculture, the weight of individual plants increased over the years, but the number of leaves per plant decreased over the years. When plants from 1995, 2002, 2009, and 2016 were grown alongside 1988 plants in equal ratios, velvetleaf gained more biomass over the years when compared to 1988 plants. Finally, plants from each year were treated with a range of imazamox and glyphosate herbicide concentrations to determine whether velvetleaf developed any tolerance to these herbicides over the years. Velvetleaf’s sensitivity to imazamox did not change over the years. However, the glyphosate response did change from 1988 to 2016. Specifically, velvetleaf developed a positive response to a low glyphosate concentration, and this positive response increased gradually from 1995 to 2016. Overall, these experiments demonstrated that velvetleaf weeds evolved rapidly from 1988 to 2016 in ways that could improve their competitiveness against crops, which is an important consideration for weed management strategies.
Technical Abstract: BACKGROUND The potential of weed species to respond to selection pressure in agroecosystems and evolve weedy traits such as competitive ability is poorly understood. This research characterized evolutionary changes in a single Abutilon theophrasti population comparing multiple generations collected from 1988 through 2016. A competition study was performed to understand changes in competitive ability and a herbicide dose-response study was carried out to assess changes in sensitivity to ALS-inhibiting herbicides and glyphosate over time. RESULTS When grown in monoculture, A. theophrasti biomass production per plant increased steadily across year-lines while leaf number decreased. In replacement experiments, A. theophrasti plants from newer year-lines were more competitive and produced more biomass and leaf area than the oldest year-line. No clear differences in sensitivity to imazamox were observed among year-lines. However, starting in 1995, this A. theophrasti population exhibited a progressive increase in hormesis in response to glyphosate at 52.5 g ae ha-1. Thus, there was 5% biomass increased per year resulting from the evolution of glyphosate hormesis, with the 2009 and 2016 year-lines having more than 50% higher biomass than the nontreated control. CONCLUSION This study demonstrated that weeds can rapidly evolve increased competitive ability. Furthermore, we provided the first direct evidence of glyphosate hormesis evolution. These results highlight the importance of considering the role that rapid evolution of weedy traits might have on the sustainability of weed management strategies.