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Interactive Effects of Deficit Irrigation and Berry Exposure Aspect on Merlot and Cabernet Sauvignon in an Arid Climate Krista C. Shellie1* Abstract: The objective of this study was to determine the main and interactive effects of a sustained water deficit during berry development and berry exposure aspect on yield and berry composition in the red winegrape cultivars Merlot and Cabernet Sauvignon. Standard (STD) and reduced (RED) levels of sustained deficit irrigation were imposed throughout berry development over four growing seasons in a field trial located in the Snake River Valley American Viticultural Area (AVA) of southwestern Idaho, United States. The STD irrigation provided ~70% of crop evapotranspiration (ETc) and the RED treatment provided ~50% of the STD. Midday leaf water potential (Ψ l) was measured weekly and the diameter of exposed east- and west-facing berries was nondestructively measured during berry development. Yield and berry maturity and the phenolic composition of exposed east- and west-facing berries were measured at harvest for each irrigation treatment. Vines under RED had lower Ψ l than vines under STD irrigation. Deficit severity and west-facing berry exposure had an additive effect on reducing berry growth. East-facing berries under STD irrigation grew faster than west-facing berries under RED irrigation. Yield per vine and berry growth were reduced in both cultivars under RED irrigation and west-facing berries contained less total monomeric anthocyanin per berry than east-facing berries. Reduction in total anthocyanin content was due to lower concentration per gram berry fresh weight in Merlot and reduced berry fresh weight in Cabernet Sauvignon. The lack of significant irrigation effect and significant exposure effect observed in this study supports the hypothesis that temperature is a major factor influencing berry compositional development. Key words: winegrape, stress, leaf water potential, Vitis vinifera L., phenolics, growth, yield

Ir rigation is used in winegrape production regions throughout the world to manage vegetative and reproductive growth and to alter berry composition (Fereres and Evans 2006). Wines produced from berries that developed under a vine water deficit (water supply below full crop-water requirement) contain sensory attributes and compounds that distinguish them from wines produced from well-watered vines (Matthews et al. 1990, Sipiora and Gutiérrez Granda 1998, Kennedy et al. 2002, Sivilotti et al. 2005, Chacón et al. 2009, Qian et al. 2009). A water deficit during berry development is usually considered beneficial for wine quality (Matthews et al. 1990) but is often achieved at the expense of a loss in yield (Shellie 2006, Keller et al. 2008). Reduced berry size, in red grapes, is thought to enhance wine quality by increasing the proportion of skin surface area to mesocarp volume (Kennedy et al. 2002, Roby et al. 2004, Ojeda et al. 2002) and by altering the rates of biosynthesis or degrada-

tion of sensorially important secondary metabolites such as flavonoids and volatile aroma compounds (Castellarin et al. 2007, Qian et al. 2009). The effects of water deficit on yield and berry composition vary according to stress severity and vine phenological stage at onset. Regulated deficit irrigation is a management technique used to exploit these principles by adjusting irrigation supply to manipulate water stress at particularly responsive phenological stages (Kriedemann and Goodwin 2003). Effective application of RDI requires precise control of water supply and accurate prediction of water demand, which is often difficult to achieve in practice. Sustained deficit irrigation is an irrigation technique that seeks to maintain a constant deficit throughout berry development by consistently supplying an amount of water to both or alternating sides of the root system that is below full crop-water requirements (de Souza et al. 2005, Fereres and Soriano 2007). Achieving the severity of water deficit that elicits a desirable physiological response without an accompanying loss of productivity requires an understanding of the fragile balance between berry growth and vine physiology. Vine response to water supply has been shown to vary among winegrape species as well as among cultivars within V. vinifera L. (Winkel and Rambal 1990, Gibberd et al. 2001, Bota et al. 2001, de Souza et al. 2005). Cabernet Sauvignon and Merlot are among the most widely planted, red-skinned winegrape cultivars worldwide, each accounting for 3% of world winegrape production (Fegan 2003). These two cultivars currently are the two most widely planted red-skinned cultivars in the Snake River Valley American Viticultural Area (AVA) (Gillerman et al. 2006). The climate of the Snake

Research Horticulturist, USDA–ARS Horticultural Crops Research Laboratory 29603, University of Idaho Lane, Parma, ID 83660. *Corresponding author (email: [email protected]) Acknowledgments: This research was conducted under ARS Project 535821000-034-00D entitled “Production Systems to Promote Yield and Quality of Grapes in the Pacific Northwest.” The author thanks Chris Rennaker, Alan Muir, and Jeff Acock for assistance in data collection, laboratory analysis, and vineyard management and the University of Idaho Parma Research and Extension Center for use of their field resources and materials. Manuscript submitted Sep 2010, revised Feb 2011, Jun 2011, accepted Jun 2011 Copyright © 2011 by the American Society for Enology and Viticulture. All rights reserved. doi: 10.5344/ajev.2011.10103 1

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Effects of Water Deficit on Merlot and Cabernet Sauvignon – 463

River Valley AVA is semiarid steppe, characterized by a dry, short, warm growing season with high solar radiation (Gillerman et al. 2006). Low seasonal precipitation (~250 mm) combined with high evaporative demand (~1254 mm pan evapotranspiration) make irrigation a necessity for winegrape production. One of the first vine responses to water deficit is a decline in vegetative growth. Control of water supply through irrigation is used to achieve a canopy vigor that balances a desired crop load. As vigor declines, canopy light transmission increases (Shellie 2006), which renders the fruit more susceptible to heat stress and/or solar injury, especially under high ambient solar radiation (Tarara et al. 2000). The surface temperature of west-facing, exposed fruit has been reported to exceed ambient temperature by as much as 16°C (Spayd et al. 2002). West-facing fruit are exposed to sunlight during the warmest part of the day and are therefore more likely than east-facing fruit to reach damaging high surface temperatures, especially under low vigor conditions. The predisposition of fruit to injury from temperature and light under irrigated field conditions has been described (Spayd et al. 2002). However, the interactive effect of a sustained water deficit and berry exposure aspect on yield and berry composition under field conditions has not been investigated. The present study was conducted to measure the main and interactive effects of water deficit and berry exposure aspect on yield and berry composition in Cabernet Sauvignon and Merlot. This paper reports results from a field trial conducted with own-rooted grapevines in an arid climate over a 4-year period.

Materials and Methods The experiment was conducted from 2002 to 2005 in a vineyard located at the University of Idaho Parma Research and Extension Center (43.78°N; 116.94°W; 750 m asl) within the Snake River Valley AVA in Parma, Idaho. Dormant cuttings of Vitis vinifera L. cvs. Cabernet Sauvignon clone 11 and Merlot clone 8 were purchased from Foundation Plant Services (University of California, Davis) and planted on their own roots in 1997 (Fallahi et al. 2004) on a 7% northfacing slope in north-to-south oriented rows with a vine by row spacing of 2.1 by 2.7 m. The soil at the trial site was a fine sandy loam over hardpan at a depth up to 1 m (Turbyfill series, Xeric Torriorthent Entisol) with an available waterholding capacity of 0.14 cm per cm of soil (USDA 1972). Vines were double-trunked, with each trunk trained into a unilateral cordon located 102 cm aboveground and spurpruned to 28 to 32 buds (14 to 16 per m cordon) per vine. Shoots were positioned vertically by trellis foliage wires and thinned around bloom to ~16 shoots per meter. No fertilizer was applied during the years of the study and pest and disease management practices were uniformly applied each year according to standard commercial practice. The vineyard was irrigated by aboveground drip with two pressure-compensated punch-in emitters (flow rate 3.8 L/hr) located ~15 cm on either side of each vine. Vines in all plots were supplied with ~50 mm of water before budbreak to establish similar soil moisture. Similar soil moisture among

subplots was assumed throughout canopy development. A standard (STD) or reduced (RED) amount of sustained deficit irrigation was supplied weekly to vines upon completion of fruit set. The STD irrigation amount replenished 70% of estimated crop evapotranspiration (ETc) and the RED treatment replenished ~50% of STD. ETc was calculated weekly following the Penman–Monteith model (Allen et al. 1998) using reference evapotranspiration (ETr) for well-watered alfalfa (http://www.usbr.gov/pn/agrimet/wxdata.html) from the 1982 Kimberly–Penman equation (Jensen et al. 1990) and a variable crop coefficient of ~0.3 at the start of irrigation treatments, ~0.8 in early August, and ~0.4 by harvest (Evans et al. 1993, Keller et al. 2008). The experiment was designed as a split-plot with two replicated blocks. Each block contained two main plots to which the irrigation treatments (STD and RED) were applied. Each main plot contained three rows with 56 vines per row. The cultivars were subplots of 8-vine panels randomly located within each main plot. The amount of water delivered in gallons to each main plot was measured by a flow meter and recorded after each irrigation event. The interior six vines of each subplot panel of Cabernet Sauvignon and Merlot were used for data collection. The same vines were evaluated each year of the study. Day of year (DOY) for budbreak, bloom, and veraison was determined by visual inspection when 50% of buds or clusters reached stages 4, 23, and 35 of the modified Eichhorn–Lorenz system (Coombe 1995). The length of one count shoot in the cordon midsection was repeatedly measured each year on four vines within each subplot from budbreak until shortly after veraison. The diameter of one berry located on the exterior, midsection of an exposed (nonshaded) cluster located on the west- and east-facing side of the vine canopy on four vines within each subplot was repeatedly measured in 2003 and 2004 from fruit set until harvest using a digital caliper on the day preceding an irrigation event. Midday Ψ l was measured on the day preceding each irrigation event on two fully expanded, exposed leaves collected from interior vines within each subplot one hour after solar noon using a pressure chamber (model 610; PMS Instruments, Corvallis, OR) as described by Turner (1988). Each cultivar was harvested when a composite must sample from 10 randomly collected clusters under STD and RED had reached a berry soluble solids concentration (SSC) of ~24% and a titratable acidity (TA) of ~6 g∙L -1. Yield per vine was calculated at harvest by weighing the clusters harvested from each of the four vines per subplot. Fruit maturity at harvest was measured from a composite must sample from three randomly collected clusters that was analyzed for SSC (refractive index detector RE40; Mettler-Toledo, Columbus, OH), pH, and TA (Metrohm 716 DMS Titrino; Brinkmann, Herisau, Switzerland) following a previous method (Shellie 2006). Pruning weight was measured on harvested vines in 2002 and 2003. Berry exposure aspect was evaluated in years 2003, 2004, and 2005. Five east-facing and five west-facing exposed clusters were collected one day prior to harvest from three vines within each subplot. The clusters were placed into labeled,

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sealed plastic bags, transported in a cooler to the laboratory, and immediately frozen at -80°C. The frozen berries were excised from the pedicel of east- and west-facing clusters, and a subsample of 20 berries was used for analysis of skin phenolics, seed number per berry, and juice hexose sugar composition. The berry skin was removed by hand as described elsewhere (Keller et al. 1998), and number of seeds per berry was recorded. Seed traces were not recorded nor counted as seeds. Juice and skins were frozen separately and kept at -80°C until analysis. Hexose sugars (glucose and fructose) in juice samples were quantified as described (Keller et al. 1998), using an HPLC system (1100 Quaternary series; Agilent, Santa Clara, CA) equipped with a refractive index (RI) detector, Cation H+ guard column (Bio-Rad Laboratories, Hercules, CA) and a Hypersil ODS C18 125 X 4 mm (5 µm) column (Hewlett Packard, Avondale, PA) using peak area and external standardization. The external standard calibration table was produced on ChemStation software with standards purchased from Sigma-Aldrich (St. Louis, MO). Phenolic compounds in the skin tissue of east- and westexposed berries under STD or RED irrigation were extracted in triplicate by soaking the skin tissue of 20 berries in 20 mL 70% (volume to volume) acetone (Fisher Scientific, Pittsburgh, PA) for 14 hr in a shaking (200 strokes∙min) water bath at 25°C, decanting, and reextracting two additional hours in 20 mL 70% acetone. The two extracts were combined and acetone removed from the sample using a rotary evaporator at 170 mbar at 30°C. The sample was diluted with deionized water to a final volume of 25 mL. Total phenols, tannins, and monomeric anthocyanins were quantified spectrophotometrically (DU 520 UVI spectrophotometer; Beckman Instruments, Fullerton, CA). Tannin content was assayed using protein precipitation (bovine serum albumin, Sigma-Aldrich) ferric chloride reagent (Fisher Scientific), and buffer solutions (Harbertson et al. 2003, Hagerman and Butler 1978) and quantified from a standard curve for catechin (catechin hydrate, Sigma-Aldrich). Total phenolic content was determined following a microscale method (Waterhouse 2002) using Folin-Ciocalteu reagent (MP

Biomedicals, Solon, OH) and quantified from a standard curve for gallic acid (Sigma-Aldrich). Total monomeric anthocyanin content was measured by pH differential (Giusti and Wrolstad 2001) and quantified based on molar absorptivity and molecular weight of malvidin-3-glucoside (Indofine Chemical, Hillsborough, NJ). Data for yield and must composition were analyzed by cultivar using a mixed model with irrigation and year as fixed effects (SAS version 8.02; SAS Institute, Cary, NC). Skin phenolic data were analyzed by cultivar using a mixed model with irrigation, exposure aspect, and year as fixed effects. Probability of significant difference among treatment levels (p ≤ 0.05) was determined using the Tukey-Kramer adjusted t test. Average pre- and postveraison Ψ l was calculated from weekly measurements and analyzed by cultivar using a mixed model with irrigation and year as fixed effects. Seasonal cumulative growing degree days (GDD) were calculated from daily maximum (no upper limit) and minimum temperature from the Parma Experiment Station weather station (U.S. Dept. of Interior, Bureau of Reclamation, Pacific Northwest Cooperative Agricultural Weather Network) using a base threshold of 10°C. Graphs presented in figures were generated using SigmaPlot 11.2 (Systat Software, San Jose, CA).

Results and Discussion Seasonal heat unit accumulation (GDD) was below the 12year average in 2002 and 2005, above the 12-year average in 2003, and similar to the 12-year average in 2004 (Table 1). Even though average seasonal precipitation during the years of this study (93 mm) provided less than 10% of average seasonal ETr (1264 mm), its annual amount inversely corresponded with seasonal ETr. Precipitation was below average in 2002 and 2003 when ETr was above average and was highest in 2005 when ETr was lowest. Seasonal ETr exceeded the 12-year site average of 1180 mm in each year of this study. Water supplied through irrigation and precipitation to vines under STD was ~27% of ETr in 2002, 2003, and 2004 and 45% of ETr in 2005. Over the four years of this study,

Table 1 Seasonal growing degree days (GDD), precipitation (Pcp), reference evapotranspiration (ETr), and irrigation amount for standard (STD) and reduced irrigation (RED) and weekly average midday leaf water potential (Ψl) preveraison (Pre-V) and postveraison (Post-V) for Cabernet Sauvignon and Merlot in a field trial in the Western Snake River Plain, Idaho. Meteorological data from the Parma Experiment Station (U.S. Dept. of Interior, Bureau of Reclamation, Pacific Northwest Cooperative Agricultural Weather Network). Average Ψl (MPa)

1 Apr–31 Oct

2002 2003 2004 2005 Avgd

GDDa (°C)

Pcp (mm)

ETrb (mm)

1581 1851 1644 1511 1636

45 75 110 142 106

1214 1382 1261 1197 1180

Irrigation (mm) STD RED 267 289 242 340

133 159 150 153

Cabernet Sauvignon Pre-Vc Post-Vc STD RED STD RED -0.97a -1.16a -1.10a -1.02a

-1.32b -1.22a -1.48b -1.21b

-1.20a -0.95a -0.91a -0.87a

-1.41b -1.19b -1.33b -1.05b

Merlot Pre-Vc Post-Vc STD RED STD RED -1.02a -1.19a -1.07a -1.00a

-1.27b -1.22a -1.38b -1.13b

-1.21a -1.11a -1.14a -1.13a

-1.44b -1.53b -1.56b -1.24b

Calculated from daily maximum (no upper limit) and minimum temperature (base threshold 10°C). ETr calculated by the 1982 Kimberly–Penman equation (Jensen et al. 1990) for well-watered alfalfa with 30 to 50 cm top growth. cMeans with different letters between STD and RED within each phenological stage for each cultivar differ significantly at p ≤ 0.05 by TukeyKramer adjusted t test. dAverage from 1993 to 2005. a b

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the amount of water supplied through irrigation to the RED treatment was 53% that of the STD treatment. The average seasonal cumulative irrigation amount for STD and RED and ETr is shown (Figure 1). STD and RED irrigation treatments were initiated on DOY 170 in 2002 and 2003 and on DOY 185 in 2004 and 2005. The 4-year seasonal amount of irrigation supplied to vines under STD in this study (285 mm) was similar to the 5-year average seasonal amount of irrigation (283 mm) supplied in a standard irrigation treatment (RDIs) in a study using Cabernet Sauvignon vines (Keller et al. 2008). However, water demand was most likely greater in Keller et al. (2008) due to closer vine spacing (1.8 m versus 2.1 m in this study), a higher number of buds per meter (20 to 23 versus 14 to 16 per m in this study), and sprawling versus vertical-shoot positioned canopy in this study. Weekly values of Ψl for vines of both cultivars under STD and RED irrigation are shown by year (Figure 2). The Ψ l of all vines was -1.0 MPa or lower when irrigation treatments were imposed and Ψ l was most negative in vines under RED. Weekly values for Ψ l decreased and increased dramatically under both irrigation treatments in some years. A similar onset and pattern of Ψ l fluctuations was apparent in both cultivars, suggesting that Ψ l values were responsive to changes in soil moisture and that the preceding irrigation provided a surplus or an insufficient amount of water relative to weekly vine demand. This explanation supports the observation that weekly measurements of Ψ l reflected weekly changes in soil moisture in a deficit irrigation field trial with own-rooted Cabernet Sauvignon (Keller et al. 2008). The surplus or insufficient amount of water applied during an irrigation event in this study was likely due to inaccurate estimates of actual ETc combined with unforeseen weekly weather events that altered water demand. Mean values pre- and postveraison for weekly Ψ l under STD and RED irrigation are shown for both cultivars (Table 1). Vines under RED had ~0.25 MPa lower Ψ l than vines

Figure 1 Cumulative seasonal irrigation amount for standard (STD) and reduced (RED) irrigation and reference evapotranspiration (ETr) calculated using the 1982 Kimberly–Penman equation (Jensen et al. 1990) for alfalfa averaged over four years (2002–2005) in Parma, ID. Onsets of phenological stages are indicated for budbreak (BB), bloom (B), veraison (V), and harvest (H).

under STD except preveraison in 2003, where Ψl was similar. In Cabernet Sauvignon, Ψl increased postveraison under both irrigation treatments in three out of four years. However, in Merlot, Ψ l under both irrigation treatments decreased postveraison by a similar amount as reported by Keller et al. (2008) for Cabernet Sauvignon under standard deficit irrigation. The greatest sustained difference in Ψ l between STD and RED occurred in both cultivars in 2004 and was ~0.33 MPa preveraison and ~0.42 MPa postveraison. The difference observed in water deficit between treatments and stress severity in 2004 was similar to that reported by Kennedy et al. (2002) for a field trial with Cabernet Sauvignon. Decline in weekly shoot growth occurred each year at a similar DOY for both cultivars and corresponded with a Ψ l at or below -1.0 MPa (data not shown). Shoot growth started declining ~DOY 170 in 2002 and 2003 and ~DOY 185 in 2004 and 2005. Slowing and cessation of vegetative growth at or below a Ψ l of -1.0 MPa has also been reported by Greenspan (2005) and by Shellie (2006). The shoot length of both cultivars was longest in 2004 (150 cm) and averaged 120 cm in 2002. The shoot length of Merlot in 2003 and 2005 (120 cm) was 40 and 20 cm longer than that of Cabernet Sauvignon. Merlot and Cabernet Sauvignon vines under RED yielded 25 and 30% less, respectively, than vines under STD (Table 2, Table 3). The berry fresh weight of Cabernet Sauvignon was 19% lower under RED than under STD. Irrigation treatment had no effect on the berry fresh weight of Merlot. Bowen et al. (2011) observed a reduction in berry fresh weight under water deficit in Merlot in two out of three years and in Cabernet Sauvignon in one out of two years. Another study reported a reduction in berry fresh weight under water deficit in three out of five years for Cabernet Sauvignon (Keller et al. 2008). Reduced berry fresh weight was found by Kennedy et al. (2002) in Cabernet Sauvignon when Ψ l differed by 0.4 MPa and declined to -1.6 MPa and by Sivilotti et al. (2005) in potted Merlot when predawn leaf water potential reached a difference of 0.5 MPa. In this study, a reduction in berry fresh weight was observed in Cabernet Sauvignon when preveraison Ψ l differed by an average of 0.25 MPa but not in Merlot when preveraison Ψ l differed by an average of 0.18 MPa. Berry growth was influenced by irrigation and exposure aspect in both cultivars (Figure 3). Growth of east-facing berries under STD irrigation was greater than west-facing berries under RED for both cultivars in both years. The difference in berry diameter between east-facing berries under STD and west-facing berries under RED was greatest in Cabernet Sauvignon. These results indicate that stress from exposure aspect and water deficit have an additive effect on berry growth. Cabernet Sauvignon had a higher percentage of one-seeded berries than Merlot (56 and 35%, respectively), although average weight per seed was similar for both cultivars (data not shown). Harbertson et al. (2002) reported an average of 1.3 seeds per berry in Cabernet Sauvignon compared to 2.8 seeds per berry in Syrah. Yokotsuka et al. (1999) reported lower berry weight in Merlot than Cabernet Sauvignon but did not report seed number per berry. These findings suggest that seed number per berry may be a cultivar or clonal trait that

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influences the sensitivity of berry growth to stress and this relationship warrants further investigation. In this study, the onset of each berry growth stage was not altered by irrigation amount and berry growth progressed, in both cultivars, as a double-sigmoid curve (Figure 3). In other research, the onset of berry growth stages also was not altered by water deficit (Sivilotti et al. 2005, Shellie 2006). Must TA was 9 and 16% lower under RED than under STD for Merlot and Cabernet Sauvignon, respectively (Table 2, Table 3). The 4-year average value for TA was 5.02 g L -1 in Merlot and 5.76 g L -1 in Cabernet Sauvignon and was similar

among years for each cultivar. The must of Merlot under RED irrigation was 0.1 pH unit higher than under STD irrigation and was similar among years. The 4-year average value for must pH was 3.71 for Merlot and 3.52 for Cabernet Sauvignon. Irrigation amount had no effect on SSC in any year and averaged 24.2 for Merlot and 23.7 for Cabernet Sauvignon. Reduced TA under water deficit with little or no effect on SSC has also been reported by others (Yokotsuka et al. 1999, Shellie 2006, Keller et al. 2008, Bowen et al. 2011). West-facing berries of Merlot and Cabernet Sauvignon contained less total monomeric anthocyanin than east-facing

Figure 2 Weekly leaf water potential of Merlot (A, B, C, D) and Cabernet Sauvignon (E, F, G, H) under two levels of sustained deficit irrigation in 2002, 2003, 2004, and 2005 in a field trial in Parma, ID. Standard irrigation (STD) provided ~70% of crop evapotranspiration and reduced (RED) irrigation provided 50% of STD. ‘V’ indicates veraison day of year. Error bars depict the standard error of the mean. Am. J. Enol. Vitic. 62:4 (2011)


berries (Table 4, Table 5). West-facing berries of Merlot had ~30% lower anthocyanin concentration and content per berry fresh weight than east-facing berries and west- and east-facing berries had similar fresh weight (1.02 and 1.09 g, respectively). West-facing Cabernet Sauvignon berries contained a similar concentration but 23% less anthocyanin per berry and weighed

10% less than east-facing berries (0.93 versus 0.84 g). Irrigation amount had no significant effect on berry total monomeric anthocyanin in either cultivar. Keller et al. (2008) found a significant decrease in color density in three out of five years in Cabernet Sauvignon under a preveraison water deficit. However, Bowen et al. (2011) found no significant effect of

Table 2 Effect of standard (STD) or reduced irrigation (RED) on yield and maturity of field-grown, own-rooted Merlot over multiple growing seasons in the Western Snake River Plain, Parma, ID.

Table 3 Effect of standard (STD) or reduced irrigation (RED) on yield and maturity of field-grown, own-rooted Cabernet Sauvignon over multiple growing seasons in the Western Snake River Plain, Parma, ID.

Irrigation STD RED Year 2002 2003 2004 2005 a

Yield (kg∙vine) *a 5.31 a 3.97 b * 6.78 a 4.74 a 4.62 a 2.42 b

Berry wt (g) ns 1.10 1.05 * 0.79 a 1.22 b 1.15 b 1.13 b

Must SSC (%) Acidity (g∙L-1) pH ns ** * 24.2 5.26 a 3.65 a 24.3 4.78 b 3.75 b ns ns ns 24.7 5.38 3.81 24.0 6.15 3.58 23.4 3.90 3.71 25.0 4.65 3.74

*, **, and ns indicate significant at p ≤ 0.05, 0.01, and not significant, respectively. Means within columns followed by different letters differ significantly at p ≤ 0.05 by Tukey-Kramer adjusted t test.

Irrigation STD RED Year 2002 2003 2004 2005 a

Yield (kg∙vine) **a 5.20 a 3.63 b * 5.69 a 4.93 a 4.79 a 2.23 b

Berry wt (g) ** 1.02 a 0.83 b ** 0.71 a 1.12 b 0.97 b 0.90 ab

Must SSC (%) Acidity (g∙L-1) ns * 24.00 6.23 a 23.40 5.26 b ns ns 23.95 6.10 23.70 5.95 23.50 5.75 23.78 5.25

pH ns 3.47 3.56 ns 3.43 3.41 3.68 3.54

*, **, and ns indicate significant at p ≤ 0.05, 0.01, and not significant, respectively. Means within columns followed by different letters differ significantly at p ≤ 0.05 by Tukey-Kramer adjusted t test.

Figure 3 Weekly diameter of exposed east- and west-facing berries (n = 8) of Merlot and Cabernet Sauvignon in 2003 and 2004 that were irrigated at ~70% crop evapotranspiration (STD) or 50% of STD (RED) in a field trial in Parma, ID. Bars depict the standard error of the mean. Am. J. Enol. Vitic. 62:4 (2011)

468 – Shellie

differing soil moisture deficits on anthocyanin concentration or content in Cabernet Sauvignon or Merlot. Romero et al. (2010) identified threshold levels of water potential for the cultivar Monastrell below which anthocyanin concentration declined. In the sunny, dry climate of southwestern Idaho, west-facing clusters in north-to-south planted vine rows receive similar amounts of daily solar radiation but reach a higher maximum temperature than east-facing clusters because they are heated by the sun when ambient temperature is often at its maximum (Spayd et al. 2002, Tarara et al. 2008). Tarara et al. (2008) associated a decrease in skin anthocyanin concentration with the duration of time that berry temperature is ~35°C and found that west-facing fruit, in a climate similar to this study, remained warmer than 35°C for twice as long as east-facing clusters. Anthocyanin concentration and content were similar among years for Merlot (0.513 mg∙g-1 and 0.532 mg∙berry, respectively) but varied by year

for Cabernet Sauvignon (Table 5). One study concluded that seasonal effects, likely climatic, were more influential on berry compositional development than imposed soil moisture deficits (Bowen et al. 2011) and another study suggested that elevated temperature rather than soil moisture was a main factor accounting for seasonal fluctuations in fruit composition (Keller et al. 2008). The lack of significant irrigation effect and significant exposure effect observed in the current study supports the suggestion that temperature has a major influence on berry anthocyanin composition. West-facing berries of Merlot had a lower concentration of glucose and fructose than east-facing berries (Table 4). Cabernet Sauvignon berries had a lower concentration of glucose and fructose under RED than under STD (Table 5). The concentration of glucose and fructose did not vary among years for either cultivar. A lower concentration of sugars in west- versus east-facing fruit and under RED versus STD is

Table 4 Effect of standard (STD) or reduced irrigation (RED) and berry exposure aspect on berry composition of field-grown, own-rooted Merlot over three growing seasons in the Western Snake River Valley, Parma, ID.

Irrigation STD RED Aspect East West Year 2003 2004 2005

Skin extract Total monomeric anthocyanina (mg∙g-1) (mg∙berry) (mg∙g-1) nsc ns ns 0.471 0.554 * 0.601a 0.424b ns 0.490 0.437 0.610

0.522 0.544 ** 0.643a 0.423b ns 0.491 0.504 0.603

Mesocarp Tanninb

0.724 0.675 ns 0.713 0.686 * 0.790a 0.698a 0.611b

(mg∙berry) **

Glucose (g∙dL-1) ns

Fructose (g∙dL-1) ns

0.805a 0.679b ns 0.775 0.709 * 0.802a 0.811a 0.613b

11.55 11.72 * 11.99a 11.28b ns 11.01 11.59 11.94

11.68 11.89 ** 12.03a 11.54b ns 11.22 12.13 12.00

Malvidin-3-glucoside equivalents, mg∙g-1 berry fresh weight, mg∙berry fresh weight. Catechin equivalents, mg∙g-1 berry fresh weight, mg∙berry fresh weight. c*, **, and ns indicate significant at p ≤ 0.05, 0.01, and not significant, respectively. Means within columns followed by different letters differ significantly at p ≤ 0.05 by Tukey-Kramer adjusted t test. a b

Table 5 Effect of standard (STD) or reduced irrigation (RED) and berry exposure aspect on berry composition of field-grown, own-rooted Cabernet Sauvignon over three growing seasons in the Western Snake River Valley, Parma, ID.

Irrigation STD RED Aspect East West Year 2003 2004 2005

Skin extract Total monomeric anthocyanina (mg∙g-1) (mg∙berry) (mg∙g-1) c ns ns ns 0.453 0.449 0.982 0.518 0.407 1.001 ns * ns 0.523 0.484a 0.974 0.448 0.372b 1.008 ** * ns 0.544a 0.494a 0.946 0.490b 0.412ab 1.047 0.423c 0.379b 0.981

Mesocarp Tanninb (mg∙berry) ns 0.964 0.777 * 0.897a 0.844b ns 0.852 0.881 0.878

Glucose (g∙dL-1) ns 11.80 11.27 ns 11.79 11.28 ns 11.66 11.45 11.49

Fructose (g∙dL-1) * 12.03a 11.49b ns 11.78 11.73 ns 11.50 12.18 11.59

Malvidin-3-glucoside equivalents, mg∙g-1 berry fresh weight, mg∙berry fresh weight. Catechin equivalents, mg∙g-1 berry fresh weight, mg∙berry fresh weight. c*, **, and ns indicate significant at p ≤ 0.05, 0.01, and not significant, respectively. Means within columns followed by different letters differ significantly at p ≤ 0.05 by Tukey-Kramer adjusted t test. a b

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likely a result of higher berry respiration driven by warmer berry temperature. An inverse correlation between berry hexose sugar concentration and temperature was noted by Kliewer (1967). Irrigation amount had a significant effect on skin tannin content in Merlot but no effect in Cabernet Sauvignon (Table 4, Table 5). Merlot berries under RED had ~16% less skin tannin per berry than berries under STD. Bowen et al. (2011) observed a reduction in tannin concentration in Cabernet Sauvignon and concentration and content in Merlot under water deficit. Romero et al. (2010) observed an increase percent reduction in extractable polyphenols under low water potential. In this study, west-facing berries of Cabernet Sauvignon had similar skin tannin concentration but 6% lower tannin content than east-facing fruit, reflecting the reduced berry fresh weight of west-facing berries.

Conclusions Throughout berry development, the midday leaf water potential in Cabernet Sauvignon and Merlot was responsive to differing amounts of water supplied under sustained deficit irrigation. Water deficit and west-facing berry exposure had additive effects on reducing berry growth, and east-facing berries under mild water stress grew larger than west-facing berries under more severe water stress. West-facing berries of both cultivars contained less total anthocyanin per berry than east-facing berries, and irrigation amount had no significant effect on anthocyanin concentration or content per berry. In Merlot, the reduction in west-facing berry anthocyanin content was due to reduced concentration per gram of berry fresh weight, but in Cabernet Sauvignon the reduction was due to reduced berry fresh weight. Under the conditions of this study, elevated temperature had a greater influence on the compositional development of Merlot and Cabernet Sauvignon berries than did soil moisture. Results from this study emphasize the importance of canopy microclimate and climatic factors in determining winegrape quality.

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