Title page:
  1. Title: Plastic response to early shade avoidance cues has season-long effect on Beta vulgaris growth and development
  2. Authors: Albert T. Adjesiwor1^, Joseph G. Ballenger1, Cynthia Weinig2, Brent Ewers2, Andrew R. Kniss1*
  3. Contact Information: Department of Plant Sciences, University of Wyoming, Laramie, WY, 82071 USA; 2Department of Botany, University of Wyoming, Laramie, WY 82071 USA;^A.T. Adjesiwor’s present address: University of Idaho, Kimberly Research and Extension Center, Kimberly, ID, 83341; *Corresponding author: Andrew R. Kniss (akniss@uwyo.edu).
  4. Funding: Funding for this research was provided by United States Department of Agriculture - National Institute of Food and Agriculture grant 2016-67013-24912, and by the Western Sugar Cooperative-Grower Joint Research Committee.
  5. Abstract: Early emerging weeds are known to negatively affect crop growth but the mechanisms by which weeds reduce crop yield are not fully understood. In a 4-yr study, we evaluated the effect of duration of weed-reflected light on sugar beet (Beta vulgarisL.) growth and development. The study included an early-season weed removal series and a late-season weed addition series of treatments arranged in a randomized complete block, and the study design ensured minimal direct resource competition. If weeds were present from emergence until the two true-leaf sugar beet stage, sugar beet leaf area was reduced 22%, leaf biomass reduced 25%, and root biomass reduced 32% compared to sugar beet grown season-long without surrounding weeds. Leaf area, leaf biomass, and root biomass was similar whether weeds were removed at the two true-leaf stage (approximately 330 GDD after planting) or allowed to remain until sugar beet harvest (approximately 1240 GDD after planting). Adding weeds at the two true-leaf stage and leaving them until harvest (~1240 GDD) reduced sugar beet leaf and root biomass by 18 and 23%, respectively. It appears sugar beet responded to weed presence by adjusting carbon allocation and leaf orientation to optimize light interception.
  6. Keywords: environmental plasticity; light quality; shade avoidance; weed competition; weed removal timing; yield potential
  7. Acknowledgments: The authors thank David Claypool who helped with the study establishment, harvesting, and processing.
Summary StatementThe presence of weed-reflected light during sugar beet emergence through the two true-leaf stage (~16 d after emergence) had a more detrimental impact on crop growth than the same environmental cue beginning at the two true-leaf stage until harvest 50 d later. Sugar beet responded irreversibly to the presence of early-season weed presence, and therefore shade avoidance may be a major contributor to sugar beet yield loss due to weeds.