Grapevine Shiraz Disease-associated viruses lead to significant yield losses by altering transcription of genes related to defence responses and photosynthesis

Grapevine Shiraz disease (SD), which is associated with Grapevine Virus A (GVA), is one of the highly destructive diseases affecting Australian and South African vineyards. However, virtually nothing is known about the transcriptional modifications in grapevine phloem tissues induced by SD as well as its impact on vine physiology, yield and fruit composition. In this study, we assessed the physiological parameters of SD-infected Vitis vinifera L. cv. Shiraz vines grown in a commercial vineyard in South Australia over two growing seasons. Viruses present in symptomatic SD-affected and asymptomatic vines were investigated using serological (ELISA) and molecular tests (PCR and Illumina next generation sequencing). SD did not alter plant water status over the growing season, however significantly decreased canopy size, leaf gas exchange, chlorophyll fluorescence, and yield. Differential gene expression analysis revealed significantly higher expression of genes associated with systemic acquired resistance (SAR) and downregulation of defence- and photosynthesis-related genes in phloem tissues of SD vines. This is the first comprehensive report of the physiological and transcriptomic responses of grapevine to SD.