Towards the diagnosis of two intracellular pathogens of grapevine in South Africa

Abstract

A survey was conducted, from 2001 to 2004, of viruses spreading within certified grapevine material in South Africa. As far as possible, viruses were identified and detection methods established. However, unknown spherical virus-like particles were observed in samples that also contained Grapevine Leafroll Associated Virus-Type 3. The unknown spherical particles were thought to most likely be Grapevine Fleck Virus, which was previously found in South Africa. A PCR method to be used locally for the routine detection of Grapevine Fleck Virus was established and first used to determine whether any of the greenhouse and field samples with the unknown spherical viruses were infected with Grapevine Fleck Virus. During the 2001 to 2004 survey, plants with leafroll and reddening symptoms unlike classical grapevine leafroll disease were also observed. No grapevine leafroll-associated viruses could be detected in these, but the symptoms observed resembled symptoms induced by phytoplasmas in Europe. A PCR method for the routine universal detection of phytoplasmas was established and this method was used to determine if phytoplasmas were associated with the symptomatic plants found. Sequence information from PCR amplicons suggest the presence of Candidatus phytoplasma solani, found for the first time in South Africa. This important finding however requires conformation by a second laboratory.