Rapid <em>Fusarium</em> head blight detection on winter wheat ears using chlorophyll fluorescence imaging

Abstract

Fusarium infection on wheat is a widespread thread for humans' and animals' nutrition as these fungi are known to produce the highly dangerous mycotoxin deoxynivaleol (DON). Besides this, Fusarium also induces head blight, a disease resulting in huge economic losses due to shrivelled and low mass or dead kerneIs. Early disease detection could help to reduce yield losses and health threads from DON contamination. The potential of chlorophyll fluorescence imaging (CFI) to yield these aims was investigated in laboratory experiments applying a FluorCam 700MF commercial CFI system. Healthy (control) plants as well as plants artificially infected with Fusarium culmorum were rated visually according to the stage of development and the degree of disease. Subsequently, a chlorophyll fluorescence image analysis of the potential maximum photochemical efficiency (F_v/F_m) was applied to determine the degree and the distribution of the damage of the ears. Between the sixth and eleventh day after artificial inoculation photosynthetic activity of single damaged kernels of diseased ears dropped to zero.
Although this only marginally affected the average maximum photochemical efficiency of entire ears, the infection led to a significant increase in the statistical distribution of F_v/F_m in the images. Pixelwise integration of F_{v(sub>/Fm-values (from low to high) of the fluorescence images allowed a differentiation, in steps of 10%, between ears of different degree of disease of 10% on in the BBCH stage 75. Lowest level of disease detection by CFI corresponded to a visually rated degree of disease of at least 5%. However, the possibility to distinguish between diseased and healthy ears became highly limited with incipient ripening of kerneIs and concomitant chlorophyll degradation at growth stage 81.
Abbreviations: CFI - chlorophyll fluorescence imaging, dai - days after inoculation, DON - deoxynivalenol, Fo - basic fluorescence emission of a dark-adapted plant, Fm - maximal fluorescence emission of a dark-adapted plant, Fv = Fm - Fo - variable fluorescence measured on dark-adapted plant, Fv/Fm - maximum fluorescence yield of PS II (photosynthetic efficiency), PS II - Photosystem II}