Plastic response to early shade avoidance cues has season‐long effect on Beta vulgaris growth and development

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-year study, we evaluated the effect of duration of weed-reflected light on sugar beet (Beta vulgaris L.) 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 minimized 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 1,240 GDD after planting).Adding weeds at the two true-leaf stage and leaving them until harvest (~1,240 GDD) reduced sugar beet leaf and root biomass by 18% and 23%, respectively. This work suggests sugar beet responds early and near-irreversibly to weed presence and has implications for crop management genetic improvement.

Relative contribution of shade avoidance and resource competition to early-season sugar beet yield loss due to weeds

“…The combined impact of shade avoidance and root interaction significantly impacted the number of sugar beet leaves and root length in the first 2 mo of growth, but all other measured response variables were primarily impacted by shade avoidance, with a substantially lesser effect of root interaction. The current field study substantiates results of previously performed large-pot studies that showed significant effects of shade avoidance on sugar beet yield potential (Adjesiwor et al 2021; Adjesiwor and Kniss 2020; Schambow et al 2019) and adds context, showing that the contribution of shade avoidance responses likely outweighs the impacts of resource depletion by weeds during the first 60 d of growth.…”

“…The combined impact of shade avoidance and root interaction significantly impacted the number of sugar beet leaves and root length in the first 2 mo of growth, but all other measured response variables were primarily impacted by shade avoidance, with a substantially lesser effect of root interaction. The current field study substantiates results of previously performed large-pot studies that showed significant effects of shade avoidance on sugar beet yield potential (Adjesiwor et al 2021 Substantial previous research on shade avoidance has characterized how plants adapt to the altered light environment caused by dense surrounding vegetation, and this work adds to that body of literature. With respect to its relevance to agronomic crops, most previous work has been done in crops harvested for seed, like corn and soybean.…”

“…Previous researchers have suggested that shade avoidance must be considered in developing the critical period of weed control in crops (Green-Tracewicz et al 2011; Page et al 2009; Rajcan et al 2004). Work by Adjesiwor et al (2021) supports the importance of shade avoidance in sugar beet, showing that even in the absence of resource competition, shade avoidance cues present from sugar beet emergence until the two true-leaf stage reduced sugar beet root biomass by 32%. The current field study presented here has demonstrated that sugar beet yield loss observed in the first 2 mo after planting is more attributable to shade avoidance than to more traditionally recognized aspects of resource competition, like water or nutrient depletion.…”

“…Volatile organic compounds such as ethylene and thigmotactic responses also play a role in the neighbor-sensing process (De Wit et al 2012; Yang and Li 2017). Neighbor sensing elicits a photomorphogenic growth pattern in plants known as the “shade avoidance response,” which has consequences for crop yield in agriculture (Adjesiwor et al 2021; Green-Tracewicz et al 2011; Rajcan and Swanton 2001; Schambow et al 2019).…”

“…Because roots are the primary economic portion of the sugar beet ( Beta vulgaris L.) plant, it makes an interesting model species for sorting out these dynamics. Previous work has shown that shade avoidance responses due to nearby weeds, even in the absence of direct resource competition, may be responsible for between 20% and 70% yield loss due to weeds in sugar beet (Adjesiwor et al 2021; Adjesiwor and Kniss 2020; Schambow et al 2019). Previous experiments in sugar beet were performed using methods that did not allow for direct root interactions or resource depletion in order to ensure the observed responses were due to shade avoidance.…”