Thielaviopsis
Important diseases: Black root rot, Damping off of many vegetables, herbaceous ornamentals and field crops, including bean, carrot, celery, cotton, gerber daisy, pansy, peas, peanut, poinsettia, soybean, squash, sweet potato, tobacco, tomato and watermelon.
Thielaviopsis is an important soil pathogen which causes root disease on a wide range of hosts, especially on bean, cucurbit and solanaceous crops.
The fungus may cause wilting and symptoms similar to other root rot diseases and/or unfavorable growing conditions. Overall wilting may or may not occur but affected plants are usually stunted and chlorotic.
Root symptoms are diagnostic; the fungus causes lesions and produces dark colored chlamydospores within the root. They often give infected roots a dark brown to black appearance. Lower stem cracking may occur on some hosts with spore production visible on affected tissue.
Thielaviopsis produces both conidia and chlamydospores. Chlamydospores are thick walled and are produced in chains in infected root tissue. They are survival structures of the fungus. Conidiophores are usually pigmented or almost clear, fatter near the base and producing conidia at the end. Conidia are clear hyaline, cylindrical and often in chains.
