Nutritional Characterization Based on Vegetation Indices to Detect Anthocyanins, Carotenoids, and Chlorophylls in Mini-Lettuce

Abstract

When obtaining new cultivars or monitoring the nutritional composition of lettuce, new techniques are necessary given the high cost and time required to conduct laboratory analyses of plant composition by conventional methods. The objective of this study was to evaluate different vegetation indices for the estimation of anthocyanin, chlorophyll, and carotenoids in mini-lettuce genotypes with different leaf colors and different typologies from red, green, and blue (RGB) images. The contents of pigments were evaluated in 15 lettuce genotypes, in addition to the soil plant analysis development (SPAD) index and vegetation indices in the visible range. The variability among genotypes was confirmed by the Scott-Knott test (p < 0.05) and multivariate analysis. Linear regressions were obtained between the green leaf index (GLI) and leaf pigments. GLI was a good predictor for estimating the contents of anthocyanin (r = −0.83; r2 = 0.75), carotenoid (r = −0.59; r2 = 0.43), chlorophyll a (r = −0.69; r2 = 0.48), chlorophyll b (r = −0.62; r2 = 0.39), and total chlorophyll (r = −0.77; r2 = 0.65) in red and green mini-lettuce. The high-performance phenotyping technique can be used to evaluate leaf pigments in breeding programs, as well as in crops for monitoring biofortification levels in lettuce.

Assessing nutritional pigment content and plant health status of green and red leafy vegetables by image analysis: Catching the “red herring” of plant digital color processing

“…A recent study using two red-leafed lettuce cultivars demonstrated the quantification of Anth via Normalized Difference Anth Index, calculated as [IR -IG]/[ IR + IG], wherein IR and IG indicate pixel intensity in the red and green wavebands, respectively (Kim and van Iersel, 2023). A similar study by Clemente et al (2023) elucidated Anth estimation in lettuce by using the Green Leaf Index, i.e., [2G -R -B]/[2G + R + B]. The present observations augment the findings of such studies to further elucidate more inclusive Anth prediction models that could be implemented for all types of leafy vegetables.…”

“…Since currently-established digital color processing protocols for monitoring plant health have been primarily developed with focus on leaf Chl and Car as key indicators of physiological status, such studies have predominantly used green-leafed plants due to the prevalence of such plants in conventional commercial cultivation (Kawashima and Nakatani, 1998;Yadav et al, 2010;Vollmann et al, 2011;Hu et al, 2013;Riccardi et al, 2014;Rigon et al, 2016;Agarwal and Dutta Gupta, 2018;Yuan et al, 2022). Conversely, the few studies carried out with red-leafed (Anth-rich) plants have primarily focused on estimating leaf Anth content (Kim and van Iersel, 2023;Clemente et al, 2023). However, co-estimation of all three types of pigments in plants remains largely unexplored, possibly owing to misleading or "red herring" trends in digital color features in the presence of high Anth concentrations.…”