Thielaviopsis basicola

Thielaviopsis basicola is a fungal plant pathogen responsible for black root rot, a disease with a large host range that includes woody and herbaceous ornamentals, agronomic crops and vegetable crops such as petunia, pansy, poinsettia, tobacco, cotton, carrot, lettuce and tomato. Its symptoms, including chlorotic lower foliage, yellowing, stunting or wilting, can resemble a nutrient deficiency, but they result from decaying root systems marked by black lesions that begin reddish and darken as the disease progresses. These lesions are caused by chlamydospores, dark resting spores the fungus produces that contribute to its pathogenicity and give infected roots their blackened appearance. This description is adapted from Wikipedia contributors under CC BY-SA 4.0; changes were made. https://creativecommons.org/licenses/by-sa/4.0/