Characterization of Closterovirus‐like Particles Associated with Grapevine Leafroll Disease

A purification procedure (Zeeet al. 1987) for closterovirus‐like particles associated with grapevine leafroll disease was improved after various sources of plant tissues, extraction buffers, pH values, and centrifugation techniques had been examined. An antiserum against the CA‐4 isolate was produced and used in ELISA. The virus‐like particles of the NY‐1 isolate measured in crude plant preparations were about 1,800 to 1,900 nm long. The molecular weight of coat protein of the NY‐1and NY‐2 isolates were ca. 43 × 103 daltons in SDS‐PAGE analysis; and bands having this molecular weight reacted in Western blotting tests with specific polyclonal and monoclonal antibodies. A large dsRNA molecule (ca. 10 × 106 Mr) along, with lower molecular weight species were isolated from leafroll diseased grapevines, but not from healthy grapevines. Seven leafroll isolates were tested for their serological relatedness in a protein A‐gold labelling immunosorbent electron microscopy, assay. Results indicated that serologically distinct serotypes existed, and mixed infection of grapevines with different scrotypes was common. A grouping of isolates into serotype I, II, III, IV is proposed.