Abstract
Although deficit irrigation is used to improve fruit quality in healthy grapevines, it can potentially amplify negative effects of viral disease and reduce fruit quality in Grapevine Red Blotch Virus (GRBV) infected grapevines. Therefore, a 2-year field experiment was conducted to understand the interaction between GRBV infection and water deficits on disease development and vine physiology. Well-watered (WW) vines were irrigated at 100% of estimated crop evapotranspiration (ETc), while water deficit (WD) vines received water at 66 and 50% ETc in 2017 and 2018, respectively. Healthy (GRBV-) and infected (GRBV+) vines were confirmed by PCR assays. There were no significant effects of water deficits on foliar symptom onset in either year, but more severe water deficits in 2018 resulted in a more rapid symptom progression. GRBV+ vines had a higher Ψstem compared to GRBV- vines, but the effects of virus only appeared post-veraison and corresponded to decreased leaf gas exchange. In general, vine vegetative and reproductive growth were not reduced in GRBV+ vines. Yields were highest in WW/GRBV+ vines due to larger clusters containing larger berries. Consistent treatment effects on berry primary chemistry were limited to sugars, with no interactions between factors. Water deficits were able to somewhat increase berry anthocyanin concentration in GRBV+ fruit, but the effects were dependent on year. By comparison, virus status and water deficits interacted on skin tannins concentration such that they were decreased in WD/GRBV+ vines, but increased in WD/GRBV- vines. Water deficits had no effect on seed phenolics, with only virus status having a significant diminution. Although keeping GRBV+ vines well-watered may mitigate some of the negative effects of GRBD, these results suggest that water deficits will not improve overall fruit quality in GRBV+ vines. Ultimately, the control of fruit ripening imparted by GRBV infection seems to be stronger than abiotic control imparted by water deficits.
Highlights
Since its discovery in 2008 in California (Calvi, 2011), Grapevine Red Blotch Disease (GRBD)—and its recently confirmed causal agent Grapevine Red Blotch Virus (GRBV) (Yepes et al, 2018)— has significantly impacted several major grape-growing areas in the United States (Sudarshana and Zalom, 2017)
This study was the first to test the hypothesis that there is an interactive effect of water deficits and GRBV infection on GRBD severity, vine growth, and fruit quality in field-grown grapevines
Each treatment factor acted more or less independently, with virus effects predominating over water deficit effects
Summary
Since its discovery in 2008 in California (Calvi, 2011), Grapevine Red Blotch Disease (GRBD)—and its recently confirmed causal agent Grapevine Red Blotch Virus (GRBV) (Yepes et al, 2018)— has significantly impacted several major grape-growing areas in the United States (Sudarshana and Zalom, 2017). No agronomic studies have been conducted testing interactions between cultural practices and their effects on physiology of GRBV-infected grapevines. More information is necessary regarding the interactive effects of GRBD and cultural practices so that producers can better manage infected vineyards. GRBV infection has been shown to affect many aspects of vine physiology from leaf metabolism (Wallis and Sudarshana, 2016) to fruit development and ripening (Blanco-Ulate et al, 2017). GRBD delays ripening and alters fruit composition through a hypothesized disruption in hormone signaling (Blanco-Ulate et al, 2017). Total soluble solids (TSS) are reduced at harvest, and berries of red-fruited has reduced polyphenolic content (Calvi, 2011; Girardello et al, 2019; Martıń ez-Lüscher et al, 2019)
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