Water Deficits Do Not Improve Fruit Quality in Grapevine Red Blotch Virus-Infected Grapevines (Vitis vinifera L.)

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 (ET c), while water deficit (WD) vines received water at 66 and 50% ET c 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 Y stem 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.

Irrigation Improves Vine Physiology and Fruit Composition in Grapevine Red Blotch Virus-Infected Vitis vinifera L.

“…Despite the fact that there were no non-infected vines in this study, there was nevertheless a significant increase in berry TSS of approximately 1 to 3 °Brix in the SUPP irrigation vines. The °Brix improvement observed in this study is within the range or greater than some reported reductions in TSS as a result of GRBV (Martínez-Lüscher et al 2019, Levin andKC 2020). While berry TSS is a useful technological marker for important production decisions such as harvest, the amount of sugar per berry is perhaps more indicative of vine carbon metabolism and more directly demonstrates the overall impact of supplemental irrigation on vine physiology.…”

“…Ultimately, the most significant result from this study was an improvement in TSS in fruit from vines that received supplemental irrigation. Studies of the impact of GRBV on vine physiology and fruit composition indicate that a reduction in TSS is the most consistent effect of the virus (Levin and KC 2020). Despite the fact that there were no non-infected vines in this study, there was nevertheless a significant increase in berry TSS of approximately 1 to 3 °Brix in the SUPP irrigation vines.…”

“…Subsequent early research related to GRBV has reported on virus detection methods (Krenz et al 2014, Al Rwahnih et al 2015, Perry et al 2016, and disease epidemiology and vector identification (Krenz et al 2014, Cieniewicz et al 2018, Dalton et al 2019. Later, more recent efforts have documented impacts of GRBV on vine physiology (Blanco-Ulate et al 2017, Martínez-Lüscher et al 2019, Bowen et al 2020, Levin and KC 2020, and reduced fruit and wine quality (Girardello et al 2019).…”

“…However, further study into disease management is necessary to offer solutions for growers, on whom the financial burden disproportionately falls. To date, only deficit irrigation has been thoroughly evaluated as a cultural practice to manage the disease beyond replacement of infected vines, but it actually proved to exacerbate the negative impacts of the virus (Levin and KC 2020). Vineyard floor management targeting insect vectors has recently been proposed, but is limited by the understanding of vectored transmission of GRBV (Bick et al 2020).…”

“…The impacts of GRBV on vine physiology may inform potential strategies for mitigating the impact of GRBV on vine health and fruit quality. A recent study reported that deficit irrigation, a common vineyard practice, may actually exacerbate the impact of the virus on vine physiology and fruit composition (Levin and KC 2020). Thus, avoiding vine water stress may prove more appropriate for virus-infected vines.…”