Leaf chlorophyll (Chl) content, at the leaf and canopy level, is an important biochemical parameter because of its crucial role in photosynthesis and in plant functioning. Furthermore, it provides an indication of the plant nutritional state and stress. Due to the reliable, rapid, and non-destructive advantages, hyperspectral remote sensing plays a significant role in monitoring and assessing the plant biophysical variables. In this study, a set of Chl-related vegetation indices (VIs) derived from the leaf reflectance data of young pepper plants infected by Cucumber Mosaic Virus (CMV) were tested for estimating the changes in the Chl content and plant status. Hyperspectral reflectance data were collected by means of a portable fiber-optics spectrometer in the spectral range of 350-1100 nm. The effect of two growth regulators, MEIA (beta-monomethyl ester of itaconic acid) and ВТН (benzo(1,2,3)thiadiazole-7-carbothioic acid-S-methyl ester), on the Chl content and respectively on the development of the viral infection was investigated too. Four categories VIs: normalized difference (ND) VIs; simple ratio (SR) VIs; single-band reflectance or simple difference (SD) VIs, and some other forms of VIs, were tested using statistical analyses (ANOVA and Tukey-Kramer’s tests) to explore their potentials in the Chl content estimation. To enhance the sensitivity of the VIs, modified VIs were tested in some other combinations of narrow bands. The statistical analyses showed that the Modified Red Edge Simple Ratio (MRESR) index, Vogelmann Red Edge index (VREI1), and Pigment index (PI) were most sensitive to the Chl content changes. The Normalized Difference VI (NDVI) and Triangular Vegetation Index (TVI) turned out to be insensitive to Chl variations. The rest of the VIs were responsible for Chl variations but with less sensitivity.

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