Tomato Blight is a fungal disease caused by the fungus Phytophthora infestans, which affects tomato plants and other members of the nightshade family. It is characterized by the appearance of dark spots on the leaves and stems of the plant, as well as the development of EDEMA, which is an accumulation of fluid in the plant tissue. The disease can spread quickly and cause significant damage to crops, leading to reduced yields and quality.