Virus Pathogens in Australian Vineyards with an Emphasis on Shiraz Disease

Abstract

Grapevine viruses are found throughout the viticultural world and have detrimental effects on vine productivity and grape and wine quality. This report provides a comprehensive and up-to-date review on grapevine viruses in Australia with a focus on "Shiraz Disease" (SD) and its two major associated viruses, grapevine virus A (GVA) and grapevine leafroll-associated virus 3 (GLRaV-3). Sensitive grapevine cultivars like Shiraz infected with GVA alone or with a co-infection of a leafroll virus, primarily GLRaV-3, show symptoms of SD leading to significant yield and quality reductions in Australia and in South Africa. Symptom descriptors for SD will be outlined and a phylogenetic tree will be presented indicating the SD-associated isolates of GVA in both countries belong to the same clade. Virus transmission, which occurs through infected propagation material, grafting, and naturally vectored by mealybugs and scale insects, will be discussed. Laboratory and field-based indexing will also be discussed along with management strategies including rogueing and replanting certified stock that decrease the incidence and spread of SD. Finally, we present several cases of SD incidence in South Australian vineyards and their effects on vine productivity. We conclude by offering strategies for virus detection and management that can be adopted by viticulturists. Novel technologies such as high throughput sequencing and remote sensing for virus detection will be outlined.

Keywords: grapevine; high throughput sequencing; leafroll disease; mealybugs; rogueing; scale insects; vectors.

Figure 1

Symptomatology of grapevine virus A (GVA)-associated Shiraz Disease. (a) primary bud necrosis shown on right; (b) restricted spring growth (front row); (c) partial lignification showing islands of green immature canes; (d) retention of crimson coloured leaves on canopy in winter.

Figure 2

Symptomatology of grapevine leafroll disease. (a) leaf margins curled downwards towards the abaxial side of the leaf; (b) interveinal regions of leaf blades appear dark red or purple in colour with distinct green veins; (c) leaves of white cultivars sometimes appear slightly chlorotic, and the veins may remain green; (d) GLRaV-4 strain 9 symptoms on Cabernet Sauvignon; (e) GLRaV-4 strain 9 symptoms on Shiraz.

Figure 3

Phylogenetic tree constructed from the alignment of full-length nucleotide sequence of the coat protein of selected isolates of GVA detected in the grapevine using neighbour-joining method (Mega 7) with 1000 bootstrap replications. Bootstrap values less than 50% are not shown. Arrowheads denote the GVA isolates from Australia studied in this work. GVD (MF774336) presents outgroup of this tree.

Figure 4

Phylogenetic tree constructed from the alignment of full-length nucleotide sequence of the coat protein of various isolates of GLRaV-3 (see also [73]) detected in the grapevine using Mega 7. A total of 1000 bootstrap replications were performed using neighbour-joining method. Bootstrap values less than 50% are not shown. Arrowheads denote the Australian isolates studied in this work. GLRaV-7 (HE588185) presents outgroup of this tree.

Figure 5

SD-infected grapevines in Australian vineyards. (a) Aerial view of a Riverland (South Australia) Shiraz vineyard showing prevalence of Shiraz disease: declining or dead vines with few or no leaves associated with GVA compared to symptomless GVA-infected Chardonnay (two rows on the right); (b) Malbec grapevines in a Langhorne Creek (South Australia) vineyard showing typical SD symptoms of restricted spring shoot growth; (c) same Shiraz block showing dieback associated with both SD and fungal trunk diseases; (d) Shiraz grapevine planted next to a stump, which tested positive for GVA two years later.