CYTOPATHOLOGY OF 2 FILAMENTOUS GRAPEVINE VIRUSES AND THEIR INTRACELLULAR IDENTIFICATION BY GOLD IMMUNOLABELING

The cytopathology of Nicotiana benthamiana cells doubly infected with grapevine corky bark-associated virus (GCBaV) and grapevine virus C (G VC), two filamentous closterolike grapevine viruses, was studied in th in sectioned leaf tissues. Whereas mesophyll parenchyma cells were app arently unaffected by the viral infection, very severe damage was suff ered by conducting tissues. Phloem cells were extensively necrotized a nd/or exhibited cell wall modifications. Membrane proliferations and v esiculations primarily originated from deranged mitochondria were extr emely frequent in phloem parenchyma and companion cells and in differe ntiating sieve elements. Virus particles were plentiful in phloem pare nchyma and companion cells, in sieve tubes and xylem elements, appeari ng as more or less compact aggregates of thin filaments localized in t he cytoplasm and, occasionally, the nucleus. As shown by differential immunogold labelling, virus aggregates were made up predominantly of G CBaV particles. GVC particles were fewer and usually intermingled with those of GCBaV.