Non-destructive Phenotyping of Lettuce Plants in Early Stages of Development with Optical Sensors

Abstract

Rapid development of plants is important for the production of ‘baby-leaf’ lettuce that is harvested when plants reach the four- to eight-leaf stage of growth. However, environmental factors, such as high or low temperature, or elevated concentrations of salt, inhibit lettuce growth. Therefore, non-destructive evaluations of plants can provide valuable information to breeders and growers. The objective of the present study was to test the feasibility of using non-destructive phenotyping with optical sensors for the evaluations of lettuce plants in early stages of development. We performed the series of experiments to determine if hyperspectral imaging and chlorophyll fluorescence imaging can determine phenotypic changes manifested on lettuce plants subjected to the extreme temperature and salinity stress treatments. Our results indicate that top view optical sensors alone can accurately determine plant size to approximately 7 g fresh weight. Hyperspectral imaging analysis was able to detect changes in the total chlorophyll (RCC) and anthocyanin (RAC) content, while chlorophyll fluorescence imaging revealed photoinhibition and reduction of plant growth caused by the extreme growing temperatures (3 and 39°C) and salinity (100 mM NaCl). Though no significant correlation was found between Fv/Fm and decrease in plant growth due to stress when comparisons were made across multiple accessions, our results indicate that lettuce plants have a high adaptability to both low (3°C) and high (39°C) temperatures, with no permanent damage to photosynthetic apparatus and fast recovery of plants after moving them to the optimal (21°C) temperature. We have also detected a strong relationship between visual rating of the green- and red-leaf color intensity and RCC and RAC, respectively. Differences in RAC among accessions suggest that the selection for intense red color may be easier to perform at somewhat lower than the optimal temperature. This study serves as a proof of concept that optical sensors can be successfully used as tools for breeders when evaluating young lettuce plants. Moreover, we were able to identify the locus for light green leaf color (qLG4), and position this locus on the molecular linkage map of lettuce, which shows that these techniques have sufficient resolution to be used in a genetic context in lettuce.

Genetic variation and relationship among content of vitamins, pigments, and sugars in baby leaf lettuce

“…Opposite, very light green‐colored “La Brillante” had very low contents of both chlorophylls and anthocyanins (Figures S2 and S3). These data confirmed a strong relationship between the content of two pigments and visual appearance of lettuce color (Gazula, Kleinhenz, Scheerens, & Ling, ; Simko et al, ). High heritability previously detected for the contents of β‐carotene, chlorophylls (Cassetari et al, ), and anthocyanins (Mamo et al, ) indicates that new cultivars and breeding lines with desirable combination of traits could be developed.…”

“…In contrary, accessions without any known pedigree relationship, such as “Dark Green Romaine” and “Green Forest,” or “La Brillante” and PI 358033‐COS, or “Little Lepricon” and PI 665200, were grouped closely together. This may be due to the fact that certain compounds, for example, anthocyanins (Gurdon et al, ; Zhang et al, ) or chlorophylls (Damerum et al, ; Hayashi et al, ; Simko et al, ), may be produced and reach similar levels in different genotypes through involvement of different genes (pathways).…”

“…Certain carotenoids, that are precursors for vitamin A biosynthesis, also have important roles in prevention of blindness due to age-related macular degeneration (Taylor & Ramsay, 2005). Anthocyanins are prominent phenolic compounds found abundantly in red-colored lettuce (Simko, Hayes, & Furbank, 2016;Sytar et al, 2018). Anthocyanin-rich lettuce demonstrated antidiabetic effects and may help in improving metabolic syndrome conditions of fatty liver and glucose metabolism (Cheng et al, 2014).…”

Sensing Technologies for Precision Phenotyping in Vegetable Crops: Current Status and Future Challenges

“…Combination of hyperspectral and fluorescence imaging was reported for lettuce (Lactuca sativa) to test phenotypic changes in early stages of development in plants subjected to extreme temperature and salinity stress treatments [96]. By means of an A-Series VNIR Micro-Hyperspec Sensor (Headwall Photonics, Fitchburg, MA, USA; 380-1012 nm), changes in chlorophyll and anthocyanin contents were measured, while a Fluor Cam 800 MF (Photon Systems Instruments, Brno, Czech Republic) was used to measure the photoinhibition due to abiotic stresses, leaf area, and growth rate.…”

Images Are More than Documentation: They Are Research Data

“…It is worth mentioning that concentrations of different substances in plant leaves are not constant but vary according to basic conditions and physiological age [5]. There are many methods for plant leaves analysis but recent trend is toward the non-destructive methods [6][7][8]. For instance, leaves shape, pigmentation and area measurements can be scored from photo.…”