Conidial germination and infection by Dipplocarpon rosae, the causal organism of rose blackspot, were examined on two resistant species of roses, Rosa roxburghii and R. wichuraiana and two susceptible hybrid tea roses (R. hybrid cv. Chicago Peace and Garden Party). Fungal conidia germinated and gave rise to subcuticular mycelium that formed haustoria within epidermal cells of all four roses tested. On the resistant rose species, epidermal cells associated with the infection site became necrotic, indicating that a hypersensitive response is involved in conferring their resistance D. rosae.
Wiggers, Robert J.; West, J. G.; and Taylor, Josephine, "Conidial Germination and Infection by Diplocarpon Rosae on Susceptible and Resistant Rose Species" (1997). Faculty Publications. 87.