Oral Presentation Science Protecting Plant Health 2017

Grapevine leafroll disease control in white cultivars (4482)

Gerhard Pietersen 1 2 3
  1. Agricultural Research Council-Plant Protection Research Institute, Pretoria, South Africa
  2. Department of Microbiology, University of Pretoria, Pretoria, South Africa
  3. Forestry and Agricultural Biotechnology Institute, University of Pretoria, Pretoria, South Africa

Grapevine leafroll disease (GLD) is associated in South Africa primarily with infection by grapevine leafroll associated virus 3 (GLRaV-3), and spread mainly by Planococcus ficus (vine mealybug). The disease affects all grapevine cultivars and is common in South African vineyards. It can be controlled by a combination of certified planting material, control of vector numbers and dissemination and roguing of infected vines. It has clear symptoms in red cultivars which can be used for roguing purposes. In white cultivars however no symptoms, or in some instances only mild symptoms are found, and visual assessment of disease cannot be used to identify infected vines for roguing. Control of GLD in white cultivars using ELISA to detect infected vines has achieved equivalent successful control of GLD as with red cultivars. At Vergelegen wine estate in Somerset West, control has been excellent in 15 white cultivar vineyards planted since 2003, with the highest single year of incidence of infection in one vineyard being only 0.6% infected in 2016. The highest cumulative infection in any vineyard was 3.6% over a nine-year period, while starting at an incidence of 0.76%. Control, based on the use of ELISA for virus detection however is very expensive and most wine estates do not consider this a viable option. Alternate methods of virus detection during control by roguing have been assessed. Loop mediated amplification of DNA (LAMP) to detect GLRaV-3 proved to be a very sensitive and allows for greater pooling of samples into one test, with concomitant reductions in cost and improved applicability. However, the technique is contamination-prone and has proven to be of limited large scale use. Following a successful proof of concept trial, we are currently assessing the novel application of an indicator bud system for disease detection in individual white cultivar vines.