Occurrence and Transmission of Grapevine Virus A in South African grapevines

Abstract

Antiserum prepared to a local isolate of grapevine virus A (GVA) was used in immunosorbent electron microscopy (lSEM) 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. GVA was found not to be associated with either stem pitting or fleck symptoms. It occurred mostly in association with undecorated c1osterovirus (CV)-like particles. Limited [SEM with decoration of the CV-Iike particles using antiserum to a Swiss isolate of CV 2200 nm, (CV type I) confirmed the pre- sence of a second CV in local grapevine sources. In addition, it indicated the presence of a third CV -like particle long- er 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 leafroll. GVA and CV type [ were also present in the vine mealybug Plano coccus ficus, following exposure to a grapevine source carrying these viruses. H"wever, due to lack of CV type [ 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. In