Cytopathology of Leafroll-Diseased Grapevines and the Purification and Serology of Associated Closteroviruslike Particles

Abstract

Thin-section electron microscopy of grapevines infected with the two leafroll isolates from California (CA-1 and CA-2) and another from New York (NY-1) revealed the presence of flexuous rod-shaped viruslike particles in the cytoplasm of phloem parenchyma cells and in the sieve elements. Particles about 10-12 mn in diameter, of undetermined length, were associated with membranous vesicles containing fibrils and electron-dense granular material characteristic of closteroviruses. Viruslike particles purified from mature symptomatic leave of grapevines infected with NY-1 and CA-1 leafroll isolates were between 1,800 and 1,900 nm long. In sodium dodecyl sulfate immunodiffusion tests, NY-1 antiserum reacted with Ca-1, CA-2, and NY-1 isolates. With indirect enzyme-linked immunosorbent assay (ELISA), NY-1 antiserum reacted more strongly to homologous than heterologous antigens, thus indicating serological differences among the isolates. With direct ELISA, the NY-1 antiserum reacted with homologous but not with the CA-2 or CA-1 antigens. The consistent association of closteroviruslike particles with the leafroll disease suports previous suggestions that closteroviruses are the causal agents of the disease. However, final proof will require the reproduction of the disease by these viruslike particles.