Comparison of the Efficiency of Hyperspectral and Pulse Amplitude Modulation Imaging Methods in Pre-Symptomatic Virus Detection in Tobacco Plants

Abstract

Early detection of pathogens can significantly reduce yield losses and improve the quality of agricultural products. This study compares the efficiency of hyperspectral (HS) imaging and pulse amplitude modulation (PAM) fluorometry to detect pathogens in plants. Reflectance spectra, normalized indices, and fluorescence parameters were studied in healthy and infected areas of leaves. Potato virus X with GFP fluorescent protein was used to assess the spread of infection throughout the plant. The study found that infection increased the reflectance of leaves in certain wavelength ranges. Analysis of the normalized reflectance indices (NRIs) revealed indices that were sensitive and insensitive to infection. NRI700/850 was optimal for virus detection; significant differences were detected on the 4th day after the virus arrived in the leaf. Maximum (Fv/Fm) and effective quantum yields of photosystem II (ΦPSII) and non-photochemical fluorescence quenching (NPQ) were almost unchanged at the early stage of infection. ΦPSII and NPQ in the transition state (a short time after actinic light was switched on) showed high sensitivity to infection. The higher sensitivity of PAM compared to HS imaging may be due to the possibility of assessing the physiological changes earlier than changes in leaf structure.

New 3-D Fluorescence Spectral Indices for Multiple Pigment Inversions of Plant Leaves via 3-D Fluorescence Spectra

“…Compared with existing fluorescence research, the newly built 3-D FSIs in this study can inverse the content of Chla and Chlb with an encouraging determination coefficient (0.8251 and 0.8696 from Table 10, respectively), but the previous research [25] only aimed to inverse leaf total chlorophyll content with a lower determination coefficient (0.73 and 0.75, respectively). The total chlorophyll fluorescence was commonly applied in the plant stress monitoring and the monitoring results, such as plant drought and disease, were not ideal for the early stage stress [64], but chlorophyll a and b both decreased rapidly in the early stage of plant stress, and the decline rate of a was faster than that of b [6]. Thus, the 3-D FSls for Chla and Chlb could provide a chance for the early stage of plant stress.…”