Pseudopezicula tracheiphila on Vitis vinifera: Microscopical studies of the infection mechanism

Electron microscopical studies of Rotbrenner pathogenesis revealed that the fungus predominantly penetrates the anticlinal cell walls of the host. Appressorium formation is not required for penetration. To improve attachment to the host surface, the infection hypha forms mucous pad. As defense reaction, secondary deposits of the cell walls of the adjacent epidermal cells were observed. After penetrating the epidermis cells, the fungus remains biotrophic. In the second stage of disease development, the biotrophic relationship between the pathogen and the host changes to perthotrophic. Near the infection sites, flavan-3-ols are localized in vacuolar inclusions of the parenchyma cells. In the spongy parenchyma, the mycelium of Pseudopezicula tracheiphila grows intracellularly with accompanying destruction of the host cells. The mycelium was detected in xylem vessels as well as in parenchymatic cells of xylem and phloem. After the hyphae invaded the vessel elements, adjacent parenchyma cells form tyloses.