SUMMARY

Ultrastructural observations were carried out on cells of Nicotiana benthamiana infected with a new me-chanically transmissible isolate of Grapevine leafroll-as-sociated virus 2 (GLRaV-2-4H), Vitis rupestris infected with the same isolate, V. vinifera cv. ‘Semillon ’ infected with GLRaV-2 isolate Se, and an undetermined V. vinifera cultivar infected with Grapevine leafroll-associ-ated virus 7 (GLRaV-7). GLRaV-2 and GLRaV-7 are members of the genus Closterovirus. Regardless of the host, both viruses appeared to multiply only in the phloem, affecting the cytology of differentiating sieve tubes, parenchyma and companion cells. Both GLRaV-2 isolates induced the same type of ultrastructural mod-ifications in the herbaceous host and Vitis, consisting primarily of membrane proliferation, formation of in-clusion bodies and virus particle aggregates. Inclusion bodies were made up of clusters of membranous vesi-cles with a fibrillar content, surrounded by a single membrane, intermixed with loose aggregates of virus particles. The vesicles did not seem to derive from mi-tochondria in both GLRaV-2 and GLRaV-7 infections, thus setting a difference between these viruses and two other grapevine closteroviruses (GLRaV-1 and GLRaV-3) previously studied. Virus particles of GLRaV-2 and GLRaV-7 were plentiful and accumulated in the cyto-plasm and nuclei of both Vitis species investigated. Key words: grapevine, closterovirus, cytopathology, immunolabelling, inclusion bodies