Nondestructive characterization of diseased Chinese chive leaves using X-ray intensity ratios with microbeam synchrotron radiation X-ray fluorescence spectrometry

The Chinese chive ( Allium tuberosum ) is a core crop grown in Kochi Prefecture, Japan. However, withering symptoms occur during greenhouse growing, which have a negative impact on crop management Chinese chive leaves with physiological disorders (PD) or necrotic streak disease (ND) present with withering as typical blight symptoms. Excess or deficiency of elements may cause such withering in Chinese chive leaves with PD. Therefore, visualizing the elemental distribution in plant bodies may help clarify the cause of this withering. In this study, using synchrotron radiation X-ray fluorescence (SR-XRF) imaging, we examined the elemental distribution conditions in healthy Chinese chive leaves without withering, those that withered due to PD, and those that withered due to ND. Segmentation analysis of inductively coupled plasma-optical emission spectroscopy (ICP-OES) was performed on the SR-XRF imaged Chinese chive leaves and the data from the two analytical methods were compared. SR-XRF imaging provided more detailed data on elemental distribution compared with segmentation analysis using ICP-OES. Based on the SR-XRF imaging results, the X-ray intensity ratios for Ca/K, Fe/Mn, and Zn/Cu were calculated. These findings support that the Ca/K, Fe/Mn, and Zn/Cu X-ray intensity ratios can be used in the early detection of withered leaves and to predict the factors causing withering. Graphical abstract