A Method for Determining the Severity of Sudden Death Syndrome in Soybeans

Sudden death syndrome (SDS), caused by the fungus Fusarium virguliforme, is a widespread mid- to late-season soybean disease with distinctive foliar symptoms that in some extreme cases may cause nearly 100% yield loss. This article reports on the development of an image analysis method to quantify SDS severity using an RGB camera under natural light in a laboratory environment. An HSI (hue, saturation, and intensity) color space based image processing approach was developed. A lesion index (LI) was defined as the ratio of affected leaf area to healthy area for evaluating SDS severity levels on leaves of infected plants. A method of using the frequency distribution of hue values of whole leaf area to measure the severity of SDS was also investigated. Preliminary results obtained from laboratory-scale validation demonstrated that the developed method could provide a feasible means of recording SDS severity in situ that could potentially be used for high-throughput greenhouse evaluation of breeding lines or commercial soybean cultivars.