Arran Rumbaugh, Blythe Durbin-Johnson, Monica Britton, Raul C. Girardello, Mysore Sudarshana, and Anita Oberholster*
*University of California, Davis, One Shields Ave, Davis, CA 95616 (aoberholster@ucdavis.edu)

Grapevine red blotch virus (GRBV), causative agent of red blotch disease, is a single-stranded DNA virus that is part of the Geminiviridae family. GRBV causes delayed ripening with significant decreases in sugar accumulation and color development that alter wine sensory characteristics. We investigated the viral impact on transcription factors and metabolite accumulation across genotypic and environmental factors. Healthy and diseased grapes were collected from Cabernet Sauvignon (CS, grafted on 420A or 110R rootstocks), at preveraison, veraison, postveraison, and harvest in 2016 and 2017. RNA in grapes was sequenced to determine viral gene expression and differences in grape gene regulation. Grape metabolites were measured using UPLC- QTOF-MS, NMR, and HS-SPME-GC-MS. Across all rootstocks and seasons, viral gene expression was greatest at preveraison, steadily decreased through ripening, and was greater in 2016 than in 2017. This correlated with fewer differences in transcription factors between healthy and infected grapes in 2017 than in 2016. Between CS 110R and CS 420A in both seasons, there were 97 common differentially expressed genes due to GRBV infection. These genes are generally responsible for key primary metabolic processes, response to stimulus, and gene silencing that could be related to viral infection. GRBV inhibited the phenylpropanoid pathway, which decreased flavonoid compound concentrations. Some metabolic pathways in postveraison and harvest samples that were induced due to GRBV are normally associated with early fruit ripening. One of these pathways was the lipoxygenase pathway, involved in synthesis of C6 alcohol and aldehyde compounds. This generally correlated with significantly lower concentrations of these compounds through ripening.

Funding Support: California Department of Food and Agriculture