CYTOPATHOLOGICAL, NEGATIVE STAINING AND SEROLOGICAL ELECTRON-MICROSCOPY OF A CLOSTERO-LIKE VIRUS ASSOCIATED WITH PEAR VEIN YELLOWS DISEASE

Ultrastructural and immunocytochemical studies were made on thin sections of Nicotiana occidentalis leaves systemically infected with a clostero-like virus associated with pear vein yellows. The virus particles were also studied in negative stain and by the decoration technique. Virus-like particles were seen only in mesophyll parenchyma cells, usually arranged in long bundles. An antiserum to apple stem pitting virus gave positive gold labelling of the virion aggregates. Labelling intensity was higher using IgG-gold than with protein A-gold. Osmium tetroxide post-fixation did not adversely affect the labelling. Virus particle morphology in negative stain resembled that of closteroviruses, although the cytopathic effects in many respects did not resemble those caused by closteroviruses; the cytoplasmic vesicles characteristic of closterovirus infections were not observed.