Advancement of grapevine maturity in Australia between 1993 and 2006: putative causes, magnitude of trends and viticultural consequences

Background and Aims: Recent warming has accelerated phenological development of many crops. We quantified the rate of change in date of designated maturity (21.8°Brix), date of harvest, and sugar concentration of berries at harvest in Chardonnay, Cabernet Sauvignon and Shiraz between 1993 and 2006. Methods and Results: Data from 18 Australian regions indicated that: (i) the date of designated maturity advanced at rates between ?0.5 and ?3.1 days/year; (ii) trends in the date of designated maturity were unrelated to trends in yield; (iii) trends of monthly temperature ranged from negligible up to 0.19°C/year; (iv) the rate of change in date of designated maturity was correlated with rate of change of temperature for Chardonnay and Cabernet Sauvignon, but not for Shiraz; (v) harvest was accelerated at a rate between ?0.4 and ?2.4 days/year; (vi) the rate of change in harvest date for Chardonnay was commensurate with the rate of change in maturity, hence berry sugar concentration at harvest remained stable with time; and (vii) the advancement of harvest for Cabernet Sauvignon and Shiraz only partially offset the advancements in maturity, hence the increase in the concentration of berry sugar at harvest, up to ~0.3°Brix/year. Conclusions: Maturity advanced at rates between half and 3 days per year. On a temperature basis, these rates are comparable to long‐term rates reported for the northern hemisphere. Significance of the Study: This is the first report of time trends in phenology of grapevine in Australia and provides a benchmark for the industry.     

Synthesis of flavonols and expression of flavonol synthase genes in the developing grape berries of Shiraz and Chardonnay (Vitis vinifera L.)

Flavonols were determined in Shiraz and Chardonnay grapes throughout berry development. The predominant flavonols were quercetin-3-glycosides with trace amounts of kaempferol-3-glycosides detected in Shiraz flowers but not in developing berries. Flavonols were present in the skin of ripening grapes but were not detected in seeds or flesh. Flavonols were also present in buds, tendrils, inflorescences, anthers and leaves. The concentration of flavonols in flowers (mg/g fresh weight) was high and decreased between flowering and berry set then remained relatively constant through berry development. The total amount of flavonols in berries (mg/berry) was low until pre-veraison then increased during berry development, particularly before veraison, the onset of ripening, in Chardonnay and during ripening in Shiraz. Two cDNA fragments with homology to genes encoding the enzyme flavonol synthase (FLS) were isolated from Shiraz flowers. In the overlapping region of the two cDNAs, they had 80% sequence identity at the nucleotide level and both had high homology to FLS genes from other plants. VvFLS1 was expressed in leaves, tendrils, pedicels, buds and inflorescences as well as in developing grapes. Expression was highest between flowering and fruit set then declined, increasing again during ripening coincident with the increase in flavonols per berry. Expression of VvFLS2 was much lower than for VvFLS1 and did not change during berry development. The results indicate that two distinct periods of flavonol synthesis occur in grapes, the first around flowering and the second during ripening of the developing berries.     

Predicting the time course of grape ripening

Background and Aim: To predict harvest time for logistic applications in vineyards and wineries, measurements of total soluble solids (TSS) are typically combined with projections assuming TSS increases at 1°Bé/week. Here, three questions were asked: (i) what is the magnitude and direction of the bias in estimates of ripening assuming 1°Bé/week across varieties, regions and seasons? (ii) what are the climatic drivers of this bias? and (iii) could thermal rates improve predictions? Methods and Results: Actual TSS of Chardonnay, Shiraz and Cabernet Sauvignon was measured in commercial vineyards in Coonawarra, Barossa Valley and Riverland. Predictions used (i) the default 1°Bé/week; (ii) variety‐ and location‐specific chronological rates between 0.8 and 1.2°Bé/week; and (iii) variety‐ and location‐specific thermal rates between 0.009 and 0.019°Bé/Cd. In eight of the nine cases, 1°Bé/week biased ripening predictions. Seasonal bias correlated with evaporative demand in the Riverland and Coonawarra and with minimum temperature in the Barossa Valley. Thermal rates were not superior to calibrated chronological rates to predict ripening. Conclusion: Locally calibrated rates significantly improved ripening predictions for major grapevine varieties in regions with contrasting climates and viticultural profiles. Significance of the Study: Improved prediction of ripeness time would allow for better allocation of key resources in vineyards and wineries – labour, time, machinery, transport, analytical services, chemicals and storage.     

Climate shifts in south‐eastern Australia: early maturity of Chardonnay,Shiraz and Cabernet Sauvignon is associated with early onset rather than faster ripening

Background and Aim: Early maturity of grape crops associated with recent warming is well documented but poorly understood. Here, we ask the question: is early maturity associated with early onset of ripening or with increased rate of sugar accumulation? Methods and Results: We used records of grape juice total soluble solids (TSS) for Chardonnay, Shiraz and Cabernet Sauvignon collected in commercial vineyards between 1995 and 2009. The combination of 15 vintages and three climatic regions yielded a range of average seasonal temperature between 15.5 and 20.5°C. Using boundary functions of TTS versus time, we derived the onset and rate of increase in TSS, and the time of maturity set at 12 °Bé for comparative purposes. Pooled across varieties, the rate of change in maturity was ?9.8 ± 0.94°C/d. Shifts in onset accounted for 86% of the variation in time of maturity and the rate of ripening for the remaining variation. Conclusion: Early maturity associated with higher temperature (and related factors including higher radiation and higher vapour pressure deficit) is primarily driven by early onset of ripening under a wide range of production systems in south‐eastern Australia. Significance of the Study: Viticultural practices aiming at delaying maturity to counteract the effect of high temperature, high radiation and high vapour pressure deficit are more likely to be successful if they target the onset of ripening.     

The effect of bunch shading on berry development and flavonoid accumulation in Shiraz grapes

Opaque boxes were applied to bunches of Shiraz grapes prior to flowering to determine the effect of sunlight on berry development and accumulation of flavonoids. The boxes were designed to maintain airflow while excluding light and thus to minimise changes in temperature and humidity. There was no significant effect of shading on sugar accumulation and in two of the three seasons studied there was no effect on berry weight. Chlorophyll concentration was much lower in the shaded fruit, which appeared pale yellow until veraison. The fruit coloured normally in the shaded bunches and in two of the three seasons there was no significant change in anthocyanin content. Expression of the gene encoding UDP-glucose flavonoid-3-O-glucosyl transferase (UFGT), a key gene in anthocyanin synthesis, increased after veraison and was similar in both shaded and exposed fruit. Anthocyanin composition was altered in the shaded fruit, which had a greater proportion of the dioxygenated anthocyanins, the glucosides of cyanidin and peonidin. Shading had no significant effect on the levels of condensed tannins in the skin or seeds of ripe fruit. Shading significantly reduced the levels of flavonols in the grape skin. In the exposed fruit, flavonol concentration was highest around flowering then declined as the berries grew, but there was an increase in flavonols per berry during ripening. When the boxes were applied before flowering, shaded fruit had much lower levels of flavonols throughout berry development and at harvest the level of flavonols were less than 10% of that in exposed fruit. A gene encoding flavonol synthase (FLS) was expressed at flowering and during ripening in exposed grapes but its expression was greatly reduced in shaded fruit. The results indicate that shading had little effect on berry development and ripening, including accumulation of anthocyanins and tannins, but significantly decreased flavonol synthesis.     

Relative proportions of seed, skin and flesh, in ripe berries from Cabernet Sauvignon grapevines grown in a vineyard either well irrigated or under water deficit

Relationships between the fresh mass of seed, skin (exocarp), and flesh (mesocarp) in six different berry size categories, were assessed on ripe fruit from Cabernet Sauvignon grapevines exposed to either High (H), Control (C) or Low (L) water status during post‐veraison berry growth in a vineyard. Berries harvested from each treatment were segregated into six mass categories in order to distinguish between changes in fresh mass components associated with general variation in berry size (on well‐watered grapevines), and those associated with berry size differences due to water stress. Berry fresh mass across all treatments ranged from about 0.4 to 2.0 g. Fresh mass components for both H and C berries comprised approximately 5% seed, 15% skin, and 80% flesh, regardless of variation in berry size, although there was some increase in seed mass relative to whole‐berry fresh mass in larger berries. Berry growth (as inferred from fresh mass at harvest) was much less sensitive to water deficit than published reports for grapevine shoot growth. Midday leaf water potentials around –1.20 MPa (Control) were not sufficient to inhibit berry growth. However, midday water potentials around –1.50 MPa (Low water status) inhibited berry growth by 13–18% of that attained by grapevines grown at high water status (i.e. treatment H where midday leaf water potentials remained around –1.00 MPa). Inhibition of berry growth by water deficit was attributed almost exclusively to reduced growth of mesocarp tissues (for most berry size categories). Water deficit thus increased the proportion of whole‐berry fresh mass represented by seeds and skin (for most berry size categories). Changes in those proportions due to irrigation treatments exceeded differences associated with general (non‐stress) variation in whole‐berry fresh mass. Excluding adverse environmental impacts on whole‐berry fresh mass, our results point to a limited role for variation in berry size per se as a factor determining the solute concentration of juice or wine derived from different sized fruit. By implication, and for all categories of whole‐berry fresh mass represented here, late season water deficit can result in ripe fruit with more skin and seed tissues (relative to whole‐berry fresh mass) compared with well‐watered control fruit.     

Influence of partial rootzone drying on the composition and accumulation of anthocyanins in grape berries (Vitis vinifera cv. Cabernet Sauvignon)

Background and Aims: The aim of the study was to investigate anthocyanin composition and accumulation in grape berries in response to the partial rootzone drying (PRD) irrigation technique.
Method and Results: The experiment was on Vitis vinifera cv. Cabernet Sauvignon, wherein PRD had a 40% water deficit relative to the control treatment. PRD decreased berry weight compared with the control, but did not influence total anthocyanin concentration. A significant increase in glucosides of delphinidin, cyanidin, petunidin and peonidin was found in response to PRD from the onset of anthocyanin accumulation (veraison), while malvidin-glucosides were unaffected by the irrigation treatment. The PRD treatment did not cause changes in the proportions of acetyl-, 3- p -coumaroyl- and monoglucoside anthocyanins. Wines produced from the treatments showed no difference in total monomeric anthocyanin, but relative increases (15%) in wine colour density, total tannin and polymeric pigment occurred in response to the PRD treatment. The anthocyanin composition of the wines reflected the response shown in the grapes, where the relative contribution of non-malvidin anthocyanins to total anthocyanins was significantly increased in wines from the PRD treatment.
Conclusions: The differences in anthocyanin composition observed in response to PRD could not be accounted for by changes in bunch microclimate, and most likely reflect differences in the methylation step of anthocyanin synthesis.
Significance of the Study: The observed changes in anthocyanin composition under the PRD irrigation system have not been previously reported in response to water deficit, and may reflect a unique response to within-vine signalling induced by PRD.