Quantification of fungal infection of leaves with digital images and Scion Image software

Digital image analysis has been used to distinguish and quantify leaf color changes arising from a variety of factors. Its use to assess the percentage of leaf area with color differences caused by plant disease symptoms, such as necrosis, chlorosis, or sporulation, can provide a rigorous and quantitative means of assessing disease severity. A method is described for measuring symptoms of different fungal foliar infections that involves capturing the image with a standard flatbed scanner or digital camera followed by quantifying the area, where the color has been affected because of fungal infection. The method uses the freely available program, Scion Image for Windows or MAC, which is derived from the public domain software, NIH Image. The method has thus far been used to quantify the percentage of tissue with necrosis, chlorosis, or sporulation on leaves of variety of plants with several different diseases (anthracnose, apple scab, powdery mildew or rust).