XVI International Botanical Congess

A conidial suspension of Diplocarpon rosae, causal organism of blackspot disease, was used to inoculate leaflets of susceptible (Rosa hybrida cv. Garden Party) and resistant (Rosa wichuraiana) plants. Samples were collected at various times post-inoculation and prepared for transmission electron microscopy (TEM) using a chemical fixation protocol. Ultrastructural features of the interaction between host and pathogen were characterized. These included haustorium formation in both hosts, the expression of early host cell death in R. wichuraiana, and the deposition of callose and delayed host cell death in R. hybrida.