Shade avoidance cues reduceBeta vulgarisgrowth

Thomas J Schambow,Andrew R Kniss,Albert T Adjesiwor,Louise Lorent

doi:10.1017/wsc.2019.2

Abstract

AbstractField and greenhouse experiments were conducted from 2013 to 2015 at the University of Wyoming to evaluate the response ofBeta vulgaris(L.) to reflected-light quality. Large-pail field studies included a factorial arrangement of three varieties ofB. vulgaris(sugar beet, table beet, and Swiss chard) and reflected-light treatments (using either colored plastic mulch, grass, or bare-soil controls). Greenhouse studies included sugar beet as influenced by either grass or soil surroundings. In all studies, grass was grown in separate containers fromB. vulgaris, so there was no root interaction. Grass was clipped regularly to prevent shading and competition for sunlight. Reflected light from different-colored plastic mulches (red, blue, green, black, clear) did not affectB. vulgarisgrowth. However, reflected light from the grass reduced the number of leaves in allB. vulgarisvarieties such that there were 10 to 14 fewer leaves inB. vulgarissurrounded by grass compared with the soil treatment at 90 d after planting in the field study. Shade avoidance cues from surrounding grass reducedB. vulgaristotal leaf area by 49% to 66%, leaf biomass by 21% to 30%, and root biomass by 70% to 72%. Similar results were observed in greenhouse experiments, where the grass treatment reduced sugar beet leaf biomass by 48% to 57% and root biomass by 35% to 64%. Shade avoidance cues have the potential to significantly reduceB. vulgarisyield, even in the absence of direct resource competition from weeds.

Highlights

Most plants absorb light in the blue-violet region (400 to 500 nm) and in the orange-red region (600 to 700 nm) but transmit or reflect light in the far-red (FR) region (700 to 800 nm)
In the 2014 field study, the grass treatment substantially reduced leaf number in all B. vulgaris varieties compared with control or plastic mulch treatments (Figure 4), so that by 90 DAP, there were 10 to 14 fewer leaves in B. vulgaris surrounded by grass compared with B. vulgaris in the soil treatment (Figure 5)
Craig and Runkle (2013) have shown that shade avoidance responses can be initiated at R:FR as low as 0.66. This supports the assertion that reduced leaf number in the grass treatment was due to the reduced R:FR, as the effect was not observed for any of the plastic mulch colors, which had a negligible effect on R:FR

Summary

Introduction

Most plants absorb light in the blue-violet region (400 to 500 nm) and in the orange-red region (600 to 700 nm) but transmit or reflect light in the far-red (FR) region (700 to 800 nm). Light reflected from plant canopies has a reduced red (R) to FR ratio (R:FR). The R:FR is a useful measurement of light quality in agricultural settings, because it relates to crops growing in weedy environments. Plants have evolved the ability to sense and respond to changes in the quality of light using a family of photoreceptors, cryptochromes and phytochromes, which act as molecular switches in response to blue-violet light and R:FR ratio, respectively (Casal 2013). The conformation change is reversible: under FR light (wavelengths neighboring 730 nm), the Pfr form of the phytochrome converts back to the Pr form (Hopkins and Huüner 2008)

Objectives

Methods

Results