Early growth, development and allometry of glyphosate-resistant and susceptible Amaranthus palmeri in response to current and elevated temperature and CO.

This study aimed to evaluate the influence of CO and temperature on glyphosate-resistant and susceptible biotypes of Amaranthus palmeri (Palmer amaranth) in terms of morphological development. Height (cm), stem diameter (cm), leaf area (cm), number of leaves, leaf, stem, and root dry matter, plant volume (m), as well as shoot-to-root allometry were evaluated. The Palmer amaranth biotypes were grown under four different scenarios: 1-low temperature (23/33 °C) and CO (410 ± 25 ppm); 2-low temperature (23/33 °C) and high CO (750 ± 25 ppm); 3-high temperature (26/36 °C) and low CO (410 ± 25 ppm); and 4-high temperature (26/36 °C) and CO (750 ± 25 ppm). Between CO and temperature, the majority of differences observed were driven by CO levels. Palmer amaranth grown under 750 ppm of CO was 15.5% taller, displayed 10% more leaf area (cm), 18% more stem dry matter, and had a 28.4% increase in volume (m) compared to 410 ppm of CO. GA2017 and GA2020 were 18% and 15.5% shorter, respectively. The number of leaves was 27% greater for GA2005. Plant volume decreased in GA2017 (35.6%) and GA2020 (23.8%). The shoot-to-root ratio was isomeric, except at 14 and 21 DAT, where an allometric growth towards shoot development was significant. Palmer amaranth biotypes responded differently to elevated CO, and the impacts of temperature need further investigation on weed physiology. Thus, environmental and genetic background may affect the response of glyphosate-resistant and susceptible populations to climate change scenarios.