Occurrence and Transmission of Grapevine Virus A in South African grapevines

Antiserum prepared to a local isolate of grapevine virus A (GVA) was used in immunosorbent electron microscopy (ISEM) with decoration and in an unlabelled antibody enzyme-linked immunosorbent assay (ELISA) for the screening of grapevine sources for the presence of virus. GV A occurred extensively in grapevine plantings showing visual symp· toms of leafroll or indexing positive for leafroll. GV A was found not to be associated with either stem pitting or fleck symptoms. It occurred mostly in association with undecorated closterovirus (CV)-like particles. Limited ISEM with decoration of the CV-like particles using antiserum to a Swiss isolate of CV 2 200 nm, (CV type I) confirmed the presence of a second CV in local grapevine sources. In addition, it indicated the presence of a third CV -like particle longer than GVA. GVA together with undecorated CV-like particles were also detected in initially GVA-free LN-33 grapevines growing under field conditions and naturally infected with Ieafroll. GV A and CV type I were also present in the vine mealybug Planococcus ficus, following exposure to a grapevine source carrying these viruses. H'lwever, due to lack of CV type I antiserum, only GV A was confirmed in grapevine following controlled transmissions with P. ficus although undecorated CV -like particles were present. The reliability of the ELISA detection procedure appears to be influenced by seasonal fluctuations in GV A concentrations

Production and use of an antiserum to grapevine virus B capsid protein purified from SDS-polyacrylamide gels

Antiserum to electrophoretically-separated capsid protein of grapevine virus B (GVB) was produced. After easy and effective elimination of antibodies cross-reactive with grapevine virus A (GVA), the antiserum was successfully used in ELISA for the detection of GVB in grapevines

Detection of two strains of grapevine leafroll-associated virus 2

Two strains of grapevine leafroll-associated virus 2 (GLRaV-2) were obtained by mechanical transmission from grapevines to Nicotiana benthantiana. The strains, designated 94/970 and 93/955, consistently differed with regard to the development of symptoms. The first induced chlorotic and occasional white-necrotic local lesions while the second induced chlorotic followed by metallic-opalescent, solid necrotic local lesions. The strains were indistinguishable with regard to the molecular weight of their capsid proteins or serologically. A difference in the pattern of minor dsRNA bands was consistently observed

Detection of Viral-like Particles by Electron Microscopy of Negatively Stained Extracts from Grapevines

Viral-like particles were detected by electron microscopy of negatively stained extracts from young leaves and roots of grapevines infected with fanleaf virus and purported to be infected with the graft-transmissible agents of Ieafroll, corky bark, fleck, and stem grooving. Preparations were extracted in 0.01 M phosphate buffer (pH 7.0) containing 2.5% nicotine and negatively stained with 2% ammonium molydate. Membrane associated spherical particles were detected in extracts from grapevines that tested positive for fanleaf virus by ELISA and bioassay. Similar membrane associated particles were detected in herbaceous plants inoculated with grapevine extracts. Rigid rod tobacco mosaic virus-like particles were detected in extracts from some grapevines but they were not disease associated. Flexuous rod viral-like particles about 11x800 nm with cross-banding helical substructure similar to closteroviruses were detected in extracts from leafroll infected grapevines

The effectiveness of in vitro somatic embryogenesis in eliminating fanleaf virus and leafroll associated viruses from grapevines

CITATION: Goussard, P. G., Wiid, J. & Kasdor, G. G. F. 1991. The effectiveness of in vitro somatic embryogenesis in eliminating fanleaf virus and leafroll associated viruses from grapevine. South African Journal of Enology & Viticulture, 12(2):77-81, doi:10.21548/12-2-2214.The original publication is available at http://www.journals.ac.za/index.php/sajevSomatic embryos were successfully regenerated from callus tissue of anthers and ovaries extracted from inflorescences of grapevines infected with grapevine fanleaf virus (GFLV) and grapevine leafroll associated viruses (GLR) respectively. Production of pro-embryogenic masses (PEMS) was controlled by specific growth regulators and culture conditions. Somatic embryos (containing roots and cotyledons) and plantlets were subjected to immunosorbent electron microscopy (ISEM) as well as serological tests (ELISA). Results indicated that somatic embryogenesis derived from ovary tissue of infected grapevines is an effective technique to eliminate grapevine Ieafroll associated viruses from grapevines but the procedure was not successful in the elimination of GFL V from anther source material.http://www.journals.ac.za/index.php/sajev/article/view/2214Publisher's versio