It is hard to get positive identification without lab testing, however this appears to be Fusarium wilt, one of the most prevalent and damaging diseases of tomatoes. The first symptom is a slight yellowing of a single leaf or a slight wilting and drooping of the lower leaves. A distinct brown discoloration of the water and food channels can be seen in a cross section of a stem close to the base of the plant.
There are many good online resources that will provide details. Most often, fusarium is present in the soil. Do NOT dump the soil in your pot into your garden. Rather, dispose of it in the trash. Once infected, soil retains this fungus indefinitely. Many tomato varieties are resistant to this and other diseases, and should be selected in the future.
Leave A Comment