Vegetation Indices for Predicting Ripening-Associated Changes in Chlorophyll and Polyphenol Content: A Multi-Cultivar Assessment in Olive Germplasm

Abstract

Vegetation indices (VIs) offer potential for non-destructive olive fruit quality moni-toring, yet their performance across diverse germplasm remains uncharacterized. This exploratory screening systematically evaluated 87 VIs for predicting chlorophyll and polyphenol content across 31 cultivars at four ripening stages, prioritizing genetic diver-sity to establish species-level biochemical-spectral relationships through integration of hyperspectral data (380-1080 nm) with biochemical analyses. Modified Chlorophyll Absorption Ratio Index and Transformed Chlorophyll Ab-sorption achieved 91 strong correlations (|r| ≥ 0.9) across 124 cultivar-stage combina-tions. High-performing indices incorporated 550 nm with red/red-edge bands (670-710 nm) and non-linear formulations. Moderate inter-cultivar variability (CV = 19.7-21.3%) in-dicated cultivar-specific calibrations may be necessary. Principal component analysis captured 99.8% of variance, revealing three biochemi-cal clusters: high-chlorophyll cultivars (n=5; 450/4078 mg/kg chlorophyll/polyphenols), typical-range cultivars (n=23; 70/4750 mg/kg), and elite cultivars (n=3; 855/6260 mg/kg), demonstrating VI capacity for cultivar discrimination. Chlorophyll degradation exhibited conserved patterns (p < 0.001), supporting uni-versal tracking models. Conversely, polyphenol dynamics displayed marked geno-type-dependency, with cultivars showing positive, negative, or minimal variation, yield-ing non-significant population-level effects (p = 0.969) despite robust cultivar-specific trends.

Code and data availability

The paper's hyperspectral reflectance measurements, chlorophyll/polyphenol reference values, and VI computation pipeline are paper-specific, but no public deposit or authors' URL is provided; the Data Availability Statement requires contacting the corresponding author. The Supplementary Materials link is a generic MDPI

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