Verticillium wilt

Verticillium wilt is caused by several species of fungal disease. It affects many garden plants including trees, shrubs, flowers, fruit and herbs but is most severe in the Solanaceae (nightshade) plant family affecting tomato, potato, eggplant and peppers.  The fungus usually enters via roots, plugs the water moving tissues (xylem), resulting in sudden and permanent wilt in the plant.  It damages leaves, stems and the fruit of the plant. 

Symptoms:

• First symptom on leaves is yellowing followed by wilting.
• Brown v-shaped lesions appear on leaves which is widest at the leaf margin. In tomatoes, this symptom is easily confused with early blight, a different disease.
• The disease affects lower leaves first and then moves upwards.
• Since the fungus damages the water moving tissues, symptoms often appear on only one side of the plant or only on one side of the leaf.
• Symptoms are more pronounced during dry periods.
• When the stem of an infected plant is cut lengthwise, the vascular tissue just under the outer skin is brown.
• Plants wilt and collapse and soon die.

Source:

Howard, R. J., Seaman, W. L., & Garland, J. A. (Eds.). (2002). Diseases and pests of vegetable crops in Canada. Vancouver, British Columbia: The Canadian Phytopathological Society and the Entomological Society of Canada.