WINETECH Technical Yearbook 2021

VITICULTURE RESEARCH | MARCH 2021

An overview on the genetic and biological variability of viruses in vineyards

DARIUSZ GOSZCZYNSKI: Plant Health and Protection, Agricultural Research Council, Pretoria KEYWORDS: Grapevine virus detection, grapevine leafroll and rugose wood diseases.

SUBSTANTIAL INPUT OF TWO SOUTH AFRICAN LABORATORIES TO WORLDWIDE KNOWLEDGE To date, 70 virus species that can infect grapevines have been recorded (Martelli, 2017). Two groups of viruses are especially detrimental for the grapevine industry from an economic point of view. These are viruses associated with grapevine leafroll (GLRD) and rugose wood diseases (GRWD). GLRD causes degeneration of phloem cells, which prevents translocation of synthesized carbohydrates from grapevine leaves. The disease delays maturation, decreases the sugar content of berries and, ultimately, negatively influences the quality of produced wine. In GRWD-affected plants, abnormal activity of cambium cells affects graft takes of cultivars to rootstocks. This leads to reduced vigour of grapevines and, ultimately, results in lower productivity and longevity of vineyards. The diseases are

easily transmitted by pests, like mealybugs and scale, which are common in vineyards. Research has revealed many virus species of the families Closteroviridae and Betaflexiviridae (Martelli, 2017) associated with these two diseases, respectively. Each species is extensively genetically heterogenic with genome differences of up to 30% between genetic variants. The genome divergence sometimes correlates with putatively different pathogenicity to grapevines. The genetic and biological data obtained for these viruses are crucial for the reliable detection of these pathogens using molecular methods, like RT-PCR, and for the ongoing study of the aetiology of these diseases. The current scientific data on viruses associated with GLRD and GRWD is the result of many years of study in various laboratories worldwide. It all began 41 years ago, in 1979, when Namba et al. in

FIGURE 1. Grapevine cv. Shiraz and LN33 infected with severe genetic variants of Grapevine virus A (GVA) and Grapevine virus B (GVB), respectively. The grapevines are also infected with GLRaV-3.

WINETECH TECHNICAL YEARBOOK 2021 | 6