What are the black structures developing inside the stem of this dying bupleurum?
These black structures are sclerotia, which are signs of the disease sclerotinia stem rot, and resting structures for the pathogen, Sclerotinia sclerotiorum. Sclerotia are hardened masses of mycelia, which enable the fungus to survive environmental stresses, such as a lack of a suitable host, high temperatures, drought or light intensity. The initial signs of sclerotinia stem rot are a white mycelial growth on the stem base around the soil line. The infection progresses to block and damage the xylem tissue, leading to chlorosis, wilting, or premature plant death. Other symptoms include stem basal rots and a black lesion at the soil surface. The pathogen has a wide host range on herbaceous plants, but is not known to infect grasses or clovers.
This week’s question is from Rob Last, Midlands Fruit and Vegetable Extension Agent.
The South Carolina Grower 