Black root rot.
Thielaviopsis basicola is a plant-pathogenic fungus in the Ascomycota phylum. It is a soil-borne fungus that causes black root rot. It has a wide host range consisting of gerbera, kalanchoe, pansy, petunia, poinsettia, primula, snapdragon, sweet pea, verbena, and viola. After T. basicola infects the host some of the symptoms consist of “stunting of foliage and root systems, blackened area on roots, yellowing of leaves between the veins or along the margins, and branch dieback. The yellowing of leaves means the plant cannot do photosynthesis and the blackened tissue means it is dead. And some of the signs include dark brown, multi-celled spores form in the infected roots. The individual cells appear to snap apart. Light colored spores are formed in a long tapering cell and extruded in chains”. If the hypocotyl along with the roots become infected it can lead to “black, rough, longitudinal cracks.”.