Detection of Grapevine Leafroll Associated Viruses on Vitis Rootstocks

Project Number
PPRI 13-31

Project title
Detection of grapevine leafroll associated viruses on Vitis rootstocks

Project leader
Pietersen, G

University of Pretoria. Department of Microbiology and Plant Pathology

Team members
Pietersen, G
Harris, M

Completion date

Project description
Grapevine leafroll associated virus 3 (GLRaV-3) does not produce symptoms and is poorly detected by ELISA and PCR in Vitis rootstocks for reasons that have not been investigated fully. During the current study we compared the virus status of the rootstock and scion within individual vines for grapevine leafroll associated virus (GLRaV-3) strains in order to understand the poor GLRaV-3 detection better. We also determined the presence in this material of other leafroll associated viruses and viruses of the Viti- and Foveavirus genera. As rootstock suckers are generally pruned away in commercial viticulture, we were unable to find sufficient specimens of all the commonly utilised rootstocks, and most samples obtained were of various scion combinations with Richter 99 rootstock (R99, V. berlandieri X V. rupestris). We confirmed the poor detection of GLRaV-3 with a broad spectrum GLRaV-3 PCR in R99 in 76 individual vines tested but also report the reliable detection of this virus in Ramsey (8 vines). We could find no clear evidence of selection of specific GLRaV-3 variants in those rootstocks which were infected by this virus. The possibility that unreported, heterogeneous, and hence poorly detected strains of GLRaV-3 may account for the poor detection of this virus in this tissue could be discounted. The possibility that the limited numbers of GLRaV-3 sources detected in R99 are resistance-breaking sources requires future investigation. Low sample numbers obtained of vines with 101-14, Richter 110, and Paulson rootstocks precluded conclusions with regards GLRaV-3 infection of these rootstocks. Investigation into the erratic distribution of GLRaV-3 and seasonal variation in distribution and titer are nearly completed. Some infections of GLRaV-1 and GLRaV-2, also in rootstocks, were observed. No infections of GLRaV-4 and -7 were obtained in any scion or rootstock tested. Members of the Viti-Foveavirus genera were readily detected in 46 of 75 R99 tested, but were present in a further 24 scions and not the corresponding R99 rootstocks. The robust detection of Viti-Foveaviruses by PCR allowed us to discount the possibility that R99 contained inhibitors that may affect PCR. We were able to show that GLRaV-1 and GLRaV-2, grapevine virus A (GVA), grapevine virus B (GVB), grapevine virus E (GVE) and grapevine rupestris stem pitting associated virus (GRSPaV) were all capable of infecting R99.

HARRIS, M., and PIETERSEN, G., 2015. Detection of grapevine leafroll associated virus-3, Viti- and Foveaviruses in Vitis rootstocks. Virology Africa 2015, Cape Town, 30 November – 3 December 2015.

HARRIS, M., AND PIETERSEN, G., 2017. Detection of grapevine leafroll associated virus 3, Viti- and Foveaviruses in Vitis rootstocks. 50th Anniversary Congress of the Southern African Society for Plant Pathology, Champagne Sports Resort, Drakensburg, 15th-18th January

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