2019 ASHS Annual Conference

Grapevine red blotch virus (GRBV) is a concern to grape industry reducing vineyard longevity, and it is suspected to alter berry ripening and chemistry. The aim of this study was to perform a physiological characterization of GRBV infected grapevines with special attention to the factors leading to inadequate grape ripening. We performed a two-year field experiment with healthy GRBV-negative (RB(-)) or infected GRBV-positive (RB(+)) Vitis vinifera 'Cabernet Sauvignon' grafted on either 110R (Vitis berlandieri × Vitis rupestris) or 420A (Vitis berlandieri × Vitis riparia), two rootstocks with different vigor and drought tolerance in Oakville, CA, USA. Leaf sugars were assessed with GC-MS. Grape berry skin flavonoids were measured using RP-HPLC. Grapevines infected with GRBV had reduced carbon fixation and stomatal conductance but only towards the end of the season; paradoxically, this was coupled to a higher stem water potential especially in 110R_RB(+). An increase in leaf soluble sugars was also found in RB(+) grapevines. Although this altered physiology was not observed consistently throughout the whole second season, both years displayed a severe reduction in berry total soluble solids (TSS) accumulation and loss of titratable acidity (TA), but not pH. Maximum anthocyanin accumulation was lower in berries from RB(+) grapevines but the differences were reduced by harvest. Contrarily, proanthocyanidins were higher in 110R_RB(+) sampled on the same date as 110R_RB(-), but not when samples with similar TSS were compared. Further comparisons of berries with the same TSS revealed a significant decoupling of must pH and anthocyanin content, but not TA, from TSS accumulation. The strong reduction in carbon import into berries (determined through TSS) under mild and transient reductions in carbon fixation suggested an impairment of translocation mechanisms in diseased vines. This may also have implications for the transport of ripening signals, other than hexoses and sucrose, which may contribute to explain why GRBV not only delayed ripening, but also decoupled ripening processes that are highly orchestrated in healthy vines.