Technical Yearbook 2023

FIGURE 6. Symptoms in Vitis vinifera. Examples of stunted shoot growth and chlorotic leaf mottling of leaves. All images provided by Dr. Elisa Angelini, CREA, Italy.

It was also determined that GFkV can be detected throughout the growing season from grapevine plants but that the highest ELISA readings, and thus optimal time for sampling, is from March to June (figure 3). We confirmed that phloem-rich tissue, either petioles and leaf veins or phloem scrapings of cane material, must be sampled and tested. In instances where cane scrapings were utilised, we demonstrated they are best extracted directly in extraction buffer, rather than pre-pulverised with liquid nitrogen. We identified petioles from basal (older) leaves as the best tissue for sampling and testing in the ELISA tests. We have shown that the ELISA is sufficiently sensitive to allow detection of one infected sample amongst five pooled together (figure 4). To better determine the ability of the ELISA to detect South African isolates of GFkV, we identified 80 sources of GFkV among 229 sampled cultivars or rootstocks from the local Vitis germplasm collection and determined the genetic variation among these. We confirmed the RNA sequence of the whole virus of 11 representative variants. The selected GFkV ELISA was used to confirm the ability of the ELISA to detect GFkV of all variant categories. We have also demonstrated that the ELISA does not detect the related virus, grapevine rupestris vein feathering virus (figure 5). To gain a measure of the incidence and possible evidence of spread of GFkV, we analysed a total of 449 samples collected from 19 vineyards by using the Agritest GFkV

ELISA. None of the samples were infected and hence no evidence of GFkV spread was obtained within this limited survey. We have established an entire protocol for the detection of GFkV by ELISA for immediate implementation, at least at a nuclear plant level, in the VIA’s certification scheme, and have recommended to the VIA and DALRDD that the most affordable kit be utilised using the protocol established through this study. Control of grapevine pinot gris virus (GPGV) through science-based phytosanitary regulations Grapevine pinot gris disease associated with grapevine pinot gris virus (GPGV) is a relatively new emerging disease of grapevines, first found in Italy in 2003. Strains of GPGV are associated with chlorotic mottling and deformations of grapevine leaves and result in reduced fruit set, uneven ripening of berries, and sometimes shoot stunting or necrosis (figure 6). Some strains of the virus however do not cause any symptoms. The disease has not been observed in South Africa and the associated virus has not been found here. However, the virus is increasingly found in countries outside of Europe after active tests for the virus were conducted in those countries. Generally, the virus in these countries is found in vines recently derived from planting material imported

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TECHNICAL YEARBOOK 2023