PathoScreen visualizes the GFP/RFP labelled pathogen and the effect of the presence of the pathogen on the plant through imaging the stress response of the plant. PathoScreen measures multiple fluorescence images at 6 megapixel resolution providing pixel-to-pixel images of Green Fluorescence Protein (GFP),Red Fluorescence Protein (RFP or DsRed), Chlorophyll Fluorescence (CF) and colour (in RGB). Modified pathogens can be selectively imaged using GFP and/or RFP labelling together with the stress response of the plant using chlorophyll fluorescence technology yielding the maximum quantum yield of Photosystem II (PSII) photochemistry (Fv/Fm). This provides early detection of the pathogen and its interaction with the photosynthesis of the plant. GFP images are corrected for auto-fluorescence from senescing leaves.