Articles
ASSOCIATION OF VIRUS PARTICLES WITH A DISEASE OF RHODODENDRON
Betty Robertson’, ‘Mrs.
W. C. Slocock’, ‘Souvenir of W.C. Slocock’, and ‘Unique’. In addition, a similar ring pattern was observed on Kalmia latifolia.
These concentric rings of necrotic tissue appeared on 2-year old leaves shortly after new growth was initiated in the spring.
As the season progressed, the rings became more numerous, and the infected leaves developed red coloration and dropped prematurely.
Symptoms were not evident on the current season’s growth or on the flowers.
Mechanical inoculations from rhododendron leaves with concentric rings and from young symptomless leaves on current season growth to 21 different herbaceous hosts failed to induce symptoms.
Grafts to symptomless rhododendrons also failed to produce symptoms.
The only successful transmission to date was when a K. latifolia plant was approach-grafted to ‘Unique’ rhododendron with symptoms.
The graft was made on 26 June 1975 and ring patterns developed two months later on two leaves immediately above the graft.
Leaf dip preparations for electron microscopic examination were made from leaf tissue of rhododendron plants in both Oregon and British Columbia.
These were negatively stained in PTA and examined in the electron microscope.
After numerous trials, one preparation revealed particles.
It was made by placing a 2 x 3 mm piece of leaf material, cut from an area of the leaf that was showing strong symptoms, in a drop of distilled water.
The tissue was cut several times with a razor blade, and then the droplet was transferred to the grid.
The grid was washed with a solution of 2% PTA. After standing 10 minutes, the excess PTA was dried off.
Two grids prepared in this manner showed a scattering of virus-like particles.
Areas containing particles were photographed at a negative magnification of 7605X and all particles that were clearly visible and intact were measured.
Although there were many particles that were fractured, most of the intact particles were within the range of 460 to 540 nm.
Of the 63