Morphological and Physiological Screening to Predict Lettuce Biomass Production in Controlled Environment Agriculture

Changhyeon Kim,Marc W. van Iersel

doi:10.3390/rs14020316

Abstract

Fast growth and rapid turnover is an important crop trait in controlled environment agriculture (CEA) due to its high cost. An ideal screening approach for fast-growing cultivars should detect desirable phenotypes non-invasively at an early growth stage, based on morphological and/or physiological traits. Hence, we established a rapid screening protocol based on a simple chlorophyll fluorescence imaging (CFI) technique to quantify the projected canopy size (PCS) of plants, combined with electron transport rate (ETR) measurements using a chlorophyll fluorometer. Eleven lettuce cultivars (Lactuca sativa), selected based on morphological differences, were grown in a greenhouse and imaged twice a week. Shoot dry weight (DW) of green cultivars at harvest 51 days after germination (DAG) was correlated with PCS at 13 DAG (R2 = 0.74), when the first true leaves had just appeared and the PCS was <8.5 cm2. However, early PCS of high anthocyanin (red) cultivars was not predictive of DW. Because light absorption by anthocyanins reduces the amount of photons available for photosynthesis, anthocyanins lower light use efficiency (LUE; DW/total incident light on canopy over the cropping cycle) and reduce growth. Additionally, the total incident light on the canopy throughout the cropping cycle explained 90% and 55% of variability in DW within green and red cultivars, respectively. Estimated leaf level ETR at a photosynthetic photon flux density (PPFD) of 200 or 1000 µmol m−2 s−1 were not correlated with DW in either green or red cultivars. In conclusion, early PCS quantification is a useful tool for the selection of fast-growing green lettuce phenotypes. However, this approach may not work in cultivars with high anthocyanin content because anthocyanins direct excitation energy away from photosynthesis and growth, weakening the correlation between incident light and growth.

Highlights

Many greenhouses and all plant factories use electric lighting, such as LED fixtures, to provide suitable light conditions for crop production
The projected canopy size (PCS) at 13 days after germination (DAG) showed a strong positive correlation with dry weight (DW) among the green lettuces (R2 = 0.76), because larger canopy size resulted in more incident light and, more biomass accumulation
Our results suggest that the PCS of young plants, before meaningful overlap of leaves within the canopy, is correlated with DW of green cultivars but not red

Summary

Introduction

Many greenhouses and all plant factories use electric lighting, such as LED fixtures, to provide suitable light conditions for crop production. Profitable crop production using electric lighting has inherent challenges due to the high cost, both installation and operating expenses, of electric lighting. Simulations of the light requirements for crop production and the cost of providing that light suggest that few crops have economic feasibility when electric lighting is the only light source [1]. To overcome the high costs associated with lighting and to maximize profits, researchers have studied different lighting strategies and developed improved cultivars for CEA [5,6]. Given the cost of providing light, efficient light capture and use are important for profitable CEA production

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