A transmission electron microscope study of "New Dawn" climber rose (Rosa wichuraiana x safrano) exhibiting rose rosette disease.

The arrival of rose rosette disease (RRD) in the Washington D.C. area prompted a transmission electron microscope study of ultrathin sections of leaves from symptomatic Rosa wichuraiana x safrano plants. Virus-like particles (VLPs) or double membrane-bound particles (DMPs) resembling those associated with RRD in other types of roses, and found in several other plant diseases, were seen in the cytoplasm of parenchymal and vascular bundle cells and shown, for the first time, in guard cells and budding into the vacuoles. Contrary to previous reports, starch granules were found in chloroplasts of the infected cells. A presumably unique intramitochondrial crystal was also observed. Variations in vacuolar content were noted.