• eggplant
• reflectance spectroscopy
• remote sensing
• salinity
• tomato
• verticillium wilt

Understanding how to achieve greater crop yield and quality with minimized environmental footprint requires advancements in high-throughput techniques to early and accurately detect and monitor the effects of biotic and abiotic stresses on plants, as well as the effectiveness of plant protection strategies. The present study deeply investigated the potential of vegetation spectroscopy to rapidly and non-destructively detect and monitor the responses of plants exposed to salt stress or challenged by the fungal pathogen Verticillium dahliae (Vd).
Two field experiments were carried out at the University of Pisa: (i) tomato plants were subjected to two salinity treatments by applying three times a week 1 L per plant of 0 or 250 mM NaCl solutions for 50 days; (ii) eggplants were root inoculated with 0 or 1×108 conidia mL-1 of Vd, and monitored for 20 days. Leaf spectral measurements (400-2,400 nm) were paired with several physiological and morphological standard measurements.
A third experiment was carried out at the University of Florida (USA), using a Scanning Plant IoT Facility (lab conditions) which provides high-throughput screening of plants via hyperspectral imaging. Here, tomato plants (cv. Celebrity) were again exposed to two salinity treatments by daily applying 500 mL per plant of 0 and 150 mM NaCl solution for 21 days.
In Italy, an array of tomato and eggplant leaf traits were well predicted by spectroscopic models (R2: 0.48-0.86). Analyzing leaf spectral signatures, it was possible to accurately discriminate both plants exposed to salt stress (from 40 days from the beginning of treatment, FBT) and those inoculated with Vd (from 10 days post inoculation, DPI) from controls. Variations of spectra-derived vegetation indices and leaf traits showed detrimental effects of salt stress on tomato at 50 days FBT, as well as of Vd infection on eggplant at 20 DPI. A UAV-multispectral sensor was flown over the tomato plants, and a red-edge/near infrared spectral index was foud as a good canopy salt stress marker.
In Florida, analyzing hyperspectral images, it was possible to discriminate with high accuracy plants under different salt stress conditions already at 3 days FBT.