Conidial germination and infection by Diplocarpon rosae on susceptible and resistant rose species

Conidial germination and infection by Diplocarpon 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. hybrida 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 to D. rosae.