Gray mold disease caused by the fungus Botrytis cinerea damages many crop hosts worldwide 9and is responsible for heavy economic losses. Early diagnosis and detection of the disease would allow 10 for more effective crop management practices to prevent outbreaks in field or greenhouse settings. 11Furthermore, having a simple, non-invasive way to quantify the extent of gray mold disease is important 12for plant pathologists interested in quantifying infection rates. In this paper, we design and build a 13 multispectral imaging system for discriminating between leaf regions, infected with gray mold, and those 14 that remain unharmed on a lettuce (Lactuca spp.) host. First, we describe a method to select two optimal 15(high contrast) spectral bands from continuous hyperspectral imagery (450-800 nm). We then built a 16 system based on these two spectral bands, located at 540 and 670 nm. The resultant system uses two 17 cameras, with a narrow band-pass spectral filter mounted on each, to measure the multispectral 18 reflectance of a lettuce leaf. The two resulting images are combined using a normalized difference 19 calculation that produces a single image with high contrast between the leaves' infected and healthy 20 regions. A classifier was then created based on the thresholding of single pixel values. We demonstrate 21 that this simple classification produces a true positive rate of 95.25% with a false positive rate of 9.316%. 22 23

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While standard visible-light imaging offers a fast and inexpensive means of quality analysis of horticultural products, it is generally limited to measuring superficial (surface) defects. Using light at longer (near-infrared) or shorter (X-ray) wavelengths enables the detection of superficial tissue bruising and density defects, respectively; however, it does not enable the optical absorption and scattering properties of sub-dermal tissue to be quantified. This paper applies visible and near-infrared interactance spectroscopy to detect internal necrosis in sweetpotatoes and develops a Zemax scattering simulation that models the measured optical signatures for both healthy and necrotic tissue. This study demonstrates that interactance spectroscopy can detect the unique near-infrared optical signatures of necrotic tissues in sweetpotatoes down to a depth of approximately 5±0.5 mm. We anticipate that light scattering measurement methods will represent a significant improvement over the current destructive analysis methods used to assay for internal defects in sweetpotatoes.

Many correlations exist between spectral reflectance or transmission with various phenotypic responses from plants. Of interest to us are metabolic characteristics, namely, how the various polarimetric components of plants may correlate to underlying environmental, metabolic, and genotypic differences among different varieties within a given species, as conducted during large field experimental trials. In this paper, we overview a portable Mueller matrix imaging spectropolarimeter, optimized for field use, by combining a temporal and spatial modulation scheme. Key aspects of the design include minimizing the measurement time while maximizing the signal-to-noise ratio by mitigating systematic error. This was achieved while maintaining an imaging capability across multiple measurement wavelengths, spanning the blue to near-infrared spectral region (405–730 nm). To this end, we present our optimization procedure, simulations, and calibration methods. Validation results, which were taken in redundant and non-redundant measurement configurations, indicated that the polarimeter provides average absolute errors of (5.3±2.2)×10−3 and (7.1±3.1)×10−3, respectively. Finally, we provide preliminary field data (depolarization, retardance, and diattenuation) to establish baselines of barren and non-barren Zea maize hybrids (G90 variety), as captured from various leaf and canopy positions during our summer 2022 field experiments. Results indicate that subtle variations in retardance and diattenuation versus leaf canopy position may be present before they are clearly visible in the spectral transmission.

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