Post-fruit Set Research Articles

Tannin and Iron-Reactive Phenolics Content in Red Cold-Hardy Hybrid Grape Tissues throughout Development and Ripening.

Phenolic compounds, especially tannins, are important for red wine quality. Wines made from cold-hardy hybrid grape cultivars have much lower tannin concentrations than wines from Vitis vinifera grape cultivars. This study assessed the phenolics content of berry tissues of three red cold-hardy hybrid cultivars in comparison to V. vinifera cv. 'Pinot noir' throughout development and ripening. Basic chemical properties, iron-reactive phenolics content, and tannin content were evaluated in the juice, skins, and seeds of Vitis spp. cvs. 'Crimson Pearl', 'Marquette', and 'Petite Pearl' and 'Pinot noir' at six time points from one week post-fruit set to harvest in 2021 and 2022. 'Crimson Pearl' displayed similar iron-reactive phenolics and tannin contents in juice, skins (22.6-25.4 mg/g dry skin and 8.0-12.2 mg/g dry skin, respectively), and seeds (12.8-29.8 mg/g dry seed and 4.2-22.0 mg/g dry seed, respectively) as 'Petite Pearl' and 'Marquette' at harvest in 2022. The hybrid cultivars showed a similar trend of phenolic accumulation as 'Pinot noir' but resulted in overall lower content in skins and seeds. Despite differences in developmental trends, the three hybrid grape cultivars displayed similar phenolic content at harvest ripeness. This is the first study examining the phenolic content of 'Crimson Pearl' and 'Petite Pearl' throughout berry development and ripening. This study provides important information for the wine industry to make informed decisions on making wine with these cultivars.

Impact of Post-Fruit Set Leaf Removal on Marquette Phenolic Compounds during Berry Development and Ripening

Impact of Post-Fruit Set Leaf Removal on Marquette Phenolic Compounds during Berry Development and Ripening

Evaluating the Effects of Early Pruning, Leaf Removal, and Shoot Thinning on ‘MidSouth’ Grapes over Two Consecutive Vintages in South Mississippi

Yield components and fruit composition of ‘MidSouth’, an interspecific hybrid bunch grape (Vitis spp.) with relatively low total soluble solids and high titratable acidity, was evaluated in south Mississippi to determine if treatments consisting of early pruning, early pruning with pre-bloom leaf removal, normal pruning with post-fruit set leaf removal, or normal pruning in one study, or post-fruit set leaf removal, post-fruit set shoot thinning, or neither leaf removal nor shoot thinning in a second study could improve these qualities. Early pruning with leaf removal reduced berries per cluster, cluster weights, yields, and Ravaz index. Early pruning treatments had inconsistent results from year to year, and normal pruning treatments were not often significantly different. Shoot thinned vines had lower yields and Ravaz index and higher total soluble solids. Second study leaf removal vines had lower juice pH in 2020 and lower yield per vine in 2021. These findings show that ‘MidSouth’ can be altered by these practices, but they did not appear to sufficiently alter ‘MidSouth’ quality. Thus, early pruning with or without leaf removal, normal pruning with leaf removal, and shoot thinning are not recommended for ‘MidSouth’ in south Mississippi, and normal pruning without these practices should be continued.

Impact of Leaf Removal on Phenolics and Antioxidant Activity of Trebbiano Berries (Vitis vinifera L.).

Leaf removal is a canopy management practice widely applied in viticulture to enhance the phenol composition and concentration of grapes, which then results in improved wine quality. Many studies were carried out on red berried varieties, but information on white ones is scanty. The aim of the study was to assess the effect of basal leaf defoliation in post fruit set on the phenol composition, ascorbate level and antioxidant activity of Trebbiano grapes. Electron paramagnetic resonance was also employed to monitor the decay kinetics of 1,1-diphenyl-2-picrylhydrazyl which allowed the identification of antioxidants with different action rates. The results show that defoliation caused an increase in the phenolic acid (hydroxycinnamic and hydroxybenzoic acids) and flavonol concentrations of berries without changes in the composition. Both ascorbate and antioxidant activity were also enhanced in the berries from defoliated vines. Besides increasing the number of fast-rate antioxidants, leaf removal resulted in the formation of intermediate-rate ones. In the Trebbiano variety, leaf removal in the post fruit set may represent an effective strategy to enhance the phenolic composition and the antioxidant defense system of berries.

Performance of Early Fruit-Zone Leaf Removal in Cabernet Sauvignon and Merlot in an Arid Climate

<h3>Summary</h3> <h3>Goals:</h3> Our goals were to evaluate how the timing of early fruit-zone leaf removal, done between prebloom and post-fruit set, influenced the risk of reduced fruit set, sunburn, and fruit quality in <i>Vitis vinifera</i> Cabernet Sauvignon and Merlot grown in the hot, arid, and irrigated region of eastern Washington State. <h3>Key Findings:</h3> Fruit set was reduced in <i>V. vinifera</i> Cabernet Sauvignon when fruit-zone leaf removal was completed during bloom. Prebloom and postbloom fruit-zone leaf removal did not reduce fruit set. Sunburn occurred on fruit on the westside of the canopy in both <i>V. vinifera</i> Cabernet Sauvignon and Merlot. Sunburn severity increased with later-timed fruit-zone leaf removal. Overall, the maximum severity of sunburn was 15% of the cluster surface area. Vintage had a greater effect on fruit quality than timing of leaf removal for both varieties. This emphasizes the need to make canopy management decisions that are informed by weather forecasts to achieve desired management goals. <h3>Impact and Significance:</h3> Early fruit-zone leaf removal was traditionally avoided in eastern Washington, in favor of completing the practice after berries have reached pea-size. The later timing of leaf removal, however, can result in sudden exposure of the fruit during the typically warmest and sunniest time of the growing season. Results from this study show that many of the assumed risks associated with early fruit-zone leaf removal, such as extreme reduction in fruit set and sunburn, are not fully realized. This means that early fruit-zone leaf removal could be adopted in this hot, arid climate without a high risk of reduction in fruit quantity or quality.

Fruit Zone Leaf Removal Timing and Extent Alters Bunch Rot, Primary Fruit Composition, and Crop Yield in Georgia-grown ‘Chardonnay’ (Vitis vinifera L.)

Fruit zone leaf removal is a vineyard management practice used to manage bunch rots, fruit composition, and crop yield. We were interested in evaluating fruit zone leaf removal effects on bunch rot, fruit composition, and crop yield in ‘Chardonnay’ grown in the U.S. state of Georgia. The experiment consisted of seven treatments: no leaf removal (NO); prebloom removal of four or six leaves (PB-4, PB-6), post–fruit set removal of four or six leaves (PFS-4, PFS-6), and prebloom removal of two or three leaves followed by post–fruit set removal of two or three leaves (PB-2/PFS-2, PB-3/PFS-3). Although leaf removal reduced botrytis bunch rot and sour rot compared with NO, effects were inconsistent across the two seasons. Fruit zone leaf removal treatments reduced titratable acidity (TA) and increased soluble solids compared with NO. PB-6 consistently reduced berry number per cluster, cluster weight, and thus crop yield relative to PFS-4. Our results show that post–fruit set fruit zone leaf removal to zero leaf layers aids in rot management, reduces TA, increases soluble solids, and maintains crop yield compared with no leaf removal. We therefore recommend post–fruit set leaf removal to zero leaf layers over no leaf removal if crops characterized by relatively greater soluble solids-to-TA ratio and reduced bunch rot are desirable for winemaking goals.

Evolution of volatile compounds during the development of Muscat grape ‘Shine Muscat’ (Vitis labrusca × V. vinifera)

This study investigated the evolution of both free and bound volatile compounds in ‘Shine Muscat’ grape from post-fruit set to post-maturity and limiting factors of the lipoxygenase (LOX) pathway. C6 compounds and terpenes were the main free and bound volatile compounds, respectively. At pre-softening, volatile compounds concentrations were mainly regulated by expansion dilution, and terpene concentrations decreased significantly, which resulted in the minimum terpene concentrations occurred at softening. The volatile compounds were mainly regulated by metabolic synthesis at post-softening, and the production of C6 compounds, terpenes and esters largely began at 10, 12 weeks post-flowering and maturity stages, respectively. In the LOX pathway, LOX, alcohol dehydrogenase and the substrate alcohols were the limiting factors. The aroma maturity stages occurred at 15.4 weeks post-flowering. Finally, the developmental patterns of the volatile compounds in grape were summarized considering previous results in neutral and non-Muscat aromatic varieties.

Intensive Fruit-zone Leaf Thinning Increases Vitis vinifera L. ‘Cabernet Sauvignon’ Berry Temperature and Berry Phenolics without Adversely Affecting Berry Anthocyanins in Virginia

Selective leaf removal in the proximity of grape clusters is a useful practice to manage fruit diseases and otherwise improve fruit composition. The current recommendation in the eastern United States is to create a fruit zone with one to two leaf layers and to focus removal on the “morning sun” side of the canopy. We evaluated a more intense and an earlier application of fruit-zone leaf thinning relative to current recommendations to determine whether additional benefits could be obtained without a penalty of impaired berry pigmentation or other ill effects of abundant grape exposure. Fruit secondary metabolites and berry temperature were monitored in two different field experiments conducted with ‘Cabernet Sauvignon’ in the northern Shenandoah Valley American Viticultural Area (AVA) of Virginia. One experiment evaluated the effects of no leaf removal, prebloom removal of four basal leaves per shoot, and prebloom removal of eight basal leaves per shoot. The other experiment evaluated the effects of no leaf removal and postfruit set removal of six basal leaves per shoot. On average, exposed grapes heated to ≥30 °C for a 126% longer period (53 hours) than shaded grapes in the postveraison period (from color development through harvest). However, postveraison grape temperatures did not remain above provisional, critical temperature thresholds of either 30 or 35 °C for as long as they did in studies conducted in sunnier, more arid climates. There were minimal differences in berry temperature between east- and west-exposed grapes in the northeast/southwest-oriented rows of the experimental vineyard. Regardless of implementation stage, leaf removal consistently increased total grape phenolics measured spectrophotometrically, and either increased or had no impact on anthocyanins relative to no leaf removal. Grape phenolics and anthocyanins were unaffected by canopy side. Berry total phenolics were increased and anthocyanins were at least maintained in fruit zones void of leaf layers—a canopy attribute that reduces bunch rot in humid regions.

Cabernet Sauvignon Responses to Prebloom and Post-Fruit Set Leaf Removal in Virginia

Summary Goals: To evaluate how variations in the extent of fruit-zone leaf thinning at prebloom or post-fruit set would affect crop yield components, cluster compactness, primary juice composition, and Botrytis bunch rot of Cabernet Sauvignon grown under Mid-Atlantic conditions in the United States. We anticipated that our results would guide leaf removal practice to target crop yield, primary juice composition, and disease management goals. Key Findings: Prebloom leaf removal reduced crop yield compared with no leaf removal, and by a greater extent when eight (59%) rather than four (25%) basal leaves per shoot were removed. Prebloom leaf removal treatments reduced crop yield by 20 to 55% compared with no leaf removal in the inaugural season, and by 50 to 77% in the third consecutive season of treatment implementation. Post-fruit set leaf removal of six basal leaves per shoot did not affect crop yield when compared to no leaf removal. Prebloom leaf removal reduced cluster compactness compared with no leaf removal, and by a greater extent when eight (47% reduction) rather than four (24% reduction) basal leaves per shoot were removed. Regardless of timing or extent, leaf removal resulted in 19 to 22% lower Botrytis bunch rot incidence compared with no leaf removal. Treatment effects on juice composition were generally unremarkable, besides lower total titratable acidities observed in leaf removal relative to no leaf removal plots. Impact and Significance: Our results illustrate that exposed grape clusters have lower bunch rot incidence and produce musts with similar pH and with lower titratable acidity than musts produced from shaded grapes. Prebloom leaf removal should be judiciously used, however, as severe crop reduction may result, particularly if prebloom leaf removal is seasonally repeated. Our results complement previous findings by (1) reporting on the effects of multiple extents of prebloom leaf removal over several consecutive growing seasons in Cabernet Sauvignon, a cultivar that is relatively resistant to bunch rots, and (2) by illustrating generally positive primary (herein) and secondary metabolite (our unpublished data) responses in harvested grapes.

Leaf Removal Effects on Cabernet franc and Petit Verdot: I. Crop Yield Components and Primary Fruit Composition

As part of a broader study of the effects of fruit exposure on fruit composition, this study aimed to evaluate how the timing and extent of leaf thinning impacted crop yield components and primary fruit composition of Cabernet franc and Petit Verdot. Treatments consisted of three post-fruit set leaf/lateral shoot removal treatments: (i) no leaf removal (NO); (ii) leaf removal from opposite the basal primary cluster and the node directly above (MED); and (iii) leaf removal from the node directly above the distal primary cluster down to the cordon (HIGH). An additional treatment applied immediately prebloom (P-B) involved removal of leaves and lateral shoots from the basal six nodes of primary shoots. Post-fruit set leaf removal had modest or no effects on crop yield components, whereas prebloom leaf removal reduced most crop yield components in both cultivars relative to the NO treatment. In both cultivars, P-B reduced crop yield by an average of 49 to 50% over two years when compared to NO, and that reduction was primarily driven by reduced cluster weight. Prebloom leaf removal implemented on the same vines in two consecutive seasons caused further reductions in crop yield in both cultivars. Both HIGH and P-B tended to depress juice Brix in Petit Verdot but not in Cabernet franc, and HIGH reduced titratable acidity more consistently than did P-B. Fruit zone leaf thinning after fruit set may balance the competing goals of improving fruit exposure, while avoiding precipitous reductions in crop yield.

Leaf Removal Effects on Cabernet franc and Petit Verdot: II. Grape Carotenoids, Phenolics, and Wine Sensory Analysis

The rationale for fruit zone leaf thinning in a humid environment is often driven more by the need for disease management than by anticipated improvements in fruit composition. Fruit zone management is often applied uniformly over climatically diverse regions, with little regard for interaction with ambient temperature or radiation. We evaluated how the timing and magnitude of fruit zone leaf and lateral removal altered fruit composition and wine consumer preference of Cabernet franc and Petit Verdot, with the underlying premise that current fruit zone management recommendations (one to two leaf layers) may be overly conservative in the humid, eastern United States. Three post-fruit set leaf/lateral shoot removal treatments (no removal [NO], removal from opposite the basal primary cluster and the node directly above [MED], and removal from the node directly above the distal primary cluster down to the cordon [HIGH]) and one pre-bloom leaf/lateral shoot removal treatment (removal from the six primary basal nodes [P-B]) were evaluated. P-B more consistently increased total berry phenolics in Petit Verdot than in Cabernet franc, while total berry anthocyanins were unaffected. Carotenoids were quantified due to their importance as aroma precursors. When compared to NO and MED, HIGH and P-B treatments tended to increase carotenoid accumulation more in the preveraison period than in the postveraison period. HIGH and P-B treatments also tended to increase carotenoid degradation more in the postveraison period, particularly for zeaxanthin. Wines made with fruit from P-B plots were ranked higher in color intensity compared to wines made with fruit from MED plots. Fruit zone leaf removal modestly improved fruit composition and wine quality potential, and created a microclimate less conducive to fungal diseases.

Water Management of Irrigated Cabernet Sauvignon Grapevines in Semi-Arid Areas

The effect of four years of deficit irrigation on water savings, yield, crop load, plant growth, and juice composition was determined on Cabernet Sauvignon grapes grown on the Central Coast of California. The growing season was divided into three periods. The first was from budburst to fruit set, during which there was no irrigation. The second was from fruit set to three weeks post-fruit set, during which 75% of calculated crop water use (ETc) was applied for all treatments. The third began three weeks post-fruit set and continued to harvest, during which irrigation resumed whenever the leaf water potential (LWP) reached −1.2 MPa in one of three sustained deficit irrigation treatments equal to 25/35% (LOW), 50% (MED), and 75/65% (HIGH) of ETc. The sum of rainfall and irrigation applied during the growing season ranged from 91 to 196 mm, from 145 to 234 mm, and from 198 to 273 mm for the LOW, MED, and HIGH treatments, respectively. Total water use, including soil water during the growing season, ranged from 250 to 359 mm, 288 to 418 mm, and 313 to 378 mm for the LOW, MED, and HIGH treatments, respectively. Yield was linearly related to the sum of irrigation and rain and to the total available water (rain, irrigation, and stored soil water) during the growing season. Yield was consistently lower in the LOW treatment across all years than in the MED and HIGH treatments; while yields in the MED and HIGH treatments were not different. Average pruning weight and cane weight declined in all treatments over the four years of the study, as did average berry size. Berry and wine composition was not affected by irrigation treatment within a given year, but were different across years due to climate, irrigation schedules, and harvest dates. Our results illustrate potential applied water savings during the growing season with moderate deficit irrigation (i.e., MED), with minimal or no significant effect on fruit yield and juice composition, while severe reduction of applied water (i.e., LOW) led to loss of yield without changing juice composition and would not be considered economically sustainable.

Effects of Leaf Removal and Applied Water on Flavonoid Accumulation in Grapevine (Vitis vinifera L. cv. Merlot) Berry in a Hot Climate.

The relationships between variations in grapevine (Vitis vinifera L. cv. Merlot) fruit zone light exposure and water deficits and the resulting berry flavonoid composition were investigated in a hot climate. The experimental design involved application of mechanical leaf removal (control, pre-bloom, post-fruit set) and differing water deficits (sustained deficit irrigation and regulated deficit irrigation). Flavonol and anthocyanin concentrations were measured by C18 reversed-phased HPLC and increased with pre-bloom leaf removal in 2013, but with post-fruit set leaf removal in 2014. Proanthocyanidin isolates were characterized by acid catalysis in the presence of excess phloroglucinol followed by reversed-phase HPLC. Post-fruit set leaf removal increased total proanthocyanidin concentration in both years, whereas no effect was observed with applied water amounts. Mean degree of polymerization of skin proanthocyanidins increased with post-fruit set leaf removal compared to pre-bloom, whereas water deficit had no effect. Conversion yield was greater with post-fruit set leaf removal. Seed proanthocyanidin concentration was rarely affected by applied treatments. The application of post-fruit set leaf removal, regardless of water deficit. increased the proportion of proanthocyanidins derived from the skin, whereas no leaf removal or pre-bloom leaf removal regardless of water deficit increased the proportion of seed-derived proanthocyanidins. The study provides fundamental information to viticulturists and winemakers on how to manage red wine grape low molecular weight phenolics and polymeric proanthocyanidin composition in a hot climate.

Anthocyanin Composition of Merlot is Ameliorated by Light Microclimate and Irrigation in Central California

An experiment was conducted in central California on Merlot to determine the interaction of time of mechanical leaf removal (control, prebloom, or post fruit-set) and irrigation amount (sustained deficit irrigation (SDI) at 0.8 of estimated vineyard evapotranspiration (ETc) or regulated deficit irrigation (RDI) at 0.8 from budbreak to fruit set, 0.5 from fruit set to veraison, and 0.8 from veraison to leaf fall) on productivity, berry skin anthocyanin concentration and composition, and unit cost per hectare. Prebloom leaf removal (applied ~100 GDD prior to bloom) consistently maintained at least 20% of photosynthetically active radiation in the fruit zone in both years of the study, while post fruit-set leaf removal was inconsistent across years. The RDI treatments reduced berry mass, while post fruit-set leaf removal reduced berry skin mass. Prebloom leaf removal did not affect yield in either year. Exposed leaf area and leaf area to fruit ratio (m2/kg) were reduced with leaf removal. The RDI consistently increased juice soluble solids. Anthocyanin concentration increased with prebloom leaf removal in both years, but irrigation treatments had no effect. The proportions of acylated and hydroxylated anthocyanins were not affected by leaf removal. In both years, SDI increased di-hydroxylated anthocyanins while RDI increased tri-hydroxylated anthocyanins. Prebloom leaf removal when combined with RDI optimized total skin anthocyanins (TSA) per hectare, while no leaf removal and SDI produced the lowest TSA. The cost to produce one unit of TSA was reduced 35% by combining prebloom leaf removal and RDI when compared to no leaf removal and SDI. This study provides information to red winegrape growers in warm regions on how to manage fruit to enhance anthocyanin concentration and the proportion of hydroxylation, while reducing input costs through mechanization and reduced irrigation.

A Five-year Study on the Effect of Cluster Thinning and Harvest Date on Yield, Fruit Composition, and Cold-hardiness of ‘Vidal Blanc’ (Vitis spp.) for Ice Wine Production

The aim of this 5-year study was to investigate the influence of cluster thinning (CT) and harvest date on yield components, fruit composition, and bud cold-hardiness in ‘Vidal blanc’ (Vitis spp.) grapevines grown in northern Ohio. It is unknown whether delaying harvest of ‘Vidal blanc’ for ice wine production would impact negatively winter-hardiness. ‘Vidal blanc’ grapevines were cluster-thinned at post-fruit set [Eichhorn-Lorenz (EL) Stage 31] to two crop levels by retaining 40 (CT40) and 60 (CT60) clusters per vine. Each crop level was harvested at three dates: normal harvest (HD1), fall harvest (HD2) after the first killing frost, and winter harvest (HD3) corresponding to the typical commercial harvest for ice wine. Generally, and as expected, the high crop level CT60 increased crop weight and cropload and decreased total soluble solids and pH. Delayed harvest decreased crop weight, cluster weight, berry weight, and titratable acidity but increased total soluble solids and pH. Bud cold-hardiness, determined by thermal analysis and after two freezing events, was not different among all treatments. It was concluded that CT40 produced optimum vine size and cropload thus balanced vines. Furthermore, delaying fruit harvest in ‘Vidal blanc’ for ice wine production in the northeastern United States and Canada improves fruit composition but has no adverse influence on bud cold-hardiness.

Irrigated Shiraz vines (Vitis vinifera) upregulate gas exchange and maintain berry growth in response to short spells of high maximum temperature in the field.

We tested the hypotheses that (i) a short period of high maximum temperature disrupts gas exchange and arrests berry growth and sugar accumulation in irrigated Shiraz vines (Vitis vinifera L.), and (ii) the magnitude of these effects depend on the phenological window when stress occur. Using a system combining passive heating (greenhouse effect) and active cooling (fans) to control daytime temperature, we compared vines heated to a nominal maximum of 40°C for three consecutive days and untreated controls. Maximum air temperature in heated treatments was 7.3°C (2006-07) and 6.5°C (2007-08) above ambient. Heat episodes were aligned with the beginning of a weekly irrigation cycle and applied in one of four phenological windows, namely post-fruit set, pre-veraison, veraison and pre-harvest. Heating systems did not affect relative humidity, hence vapour pressure deficit (VPD) was increased in the heated treatments and tracked the daily cycle of temperature. Heat did not affect the dynamics of berry growth and sugar accumulation, except for a 16% reduction in berry size and sugar content in vines heated shortly after fruit set in 2006-07. Vines upregulated stomatal conductance and gas exchange in response to heat. Stomatal conductance, photosynthesis and transpiration at a common VPD were consistently higher in heated vines than in controls. We suggest that stomatal behaviour previously described as part of Shiraz anisohydric syndrome may be adaptive in terms of heat tolerance at the expense of short-term transpiration efficiency.

The Effect of Partial Defoliation on Vine Carbohydrate Concentration and Flavonoid Production in Cranberries

The effect of partial defoliation (rate and timing) on vine carbohydrate concentration and the development of phenolic compounds in field-grown `Stevens' cranberry fruit was investigated in two experiments. In Expt. 1, partial defoliation rates of 0%, 18%, 39%, and 53% of total leaf area were applied before new growth, at fruit set, at midfruit development, and preharvest. In Expt. 2, treatments of 0% and 34% removal of new leaves were applied at postfruit set, and at midfruit development. In both experiments, upright samples were harvested for carbohydrate analysis 10d after defoliation, and fruit were removed for analysis before commercial harvest of the site. While total berry phenolic concentration was unaffected by partial defoliation in both studies, the separate pools of flavonoid compounds were affected differently by treatment. In Expt. 1, total flavonol concentration at harvest was improved by the highest rate of partial defoliation (53% of total leaf area) at both fruit set and midfruit development. Total anthocyanin concentration was improved by partial defoliation rates of 39% and 53% of total leaf area compared to the 18% defoliation treatment, but was not affected by timing of defoliation. Pearson correlation coefficients indicated that total flavonol concentration was positively correlated with vine total nonstructural carbohydrate concentration at preharvest, while total anthocyanin concentration was negatively correlated with vine soluble carbohydrates, starch, and total nonstructural carbohydrate concentration at midfruit development. In Expt. 2, total phenolics, flavonols, and anthocyanins were unaffected by partial defoliation; however there was a negative correlation between total anthocyanin concentration in the fruit and soluble carbohydrate concentration in the vine at midfruit development. In these experiments, partial defoliation early in the growing season improved total flavonols and total anthocyanins. Production of flavonols and anthocyanins appeared to be regulated independently of each other.

Evaluation of Grapevine `Cabernet Sauvignon' Response to Two Deficit Irrigation Strategies

Partial rootzone drying (PRD) and regulated deficit irrigation (RDI) were evaluated separately over two years on Vitis vinifera L. variety `Cabernet Sauvignon' for their applicability to commercial vineyards in Texas and to investigate their potential for enhancing grapevine acclimation and cold hardiness. PRD treatments compared the alternating-half-rootzone water application strategy of PRD to an equal volume of water applied to the entire rootzone and a 2× volume of water applied to the entire rootzone. RDI treatments compared the effects of deficit irrigation at different developmental stages of grapevine: post-fruit set to veraison; veraison to harvest; post-harvest; and a no-deficit control. The PRD treatment plots performed similarly to the equal volume treatment plots for yield and fruit composition. The double-volume treatment had a trend to higher yield in 2002 and statistically significant higher yields in 2003, and slightly lower soluble solids content of fruit in 2002. Thus, the two deficit treatments, PRD and Equal, experienced only a small reduction in performance while enabling reduced water usage. The PRD alternating-half-rootzone strategy demonstrated no advantage over a standard deficit irrigation strategy. Grapevines irrigated with the RDI strategy responded to this treatment most during the post-fruit set to veraison stage of development, which had lower yields and higher fruit soluble solids compared to the no-deficit treatment in 2002. Both PRD and RDI deficit irrigation strategies significantly increased the earliness and rate of periderm development on shoots in both years, but did not result in consistently greater cold hardiness compared to no-deficit treatments.

Response to nitrogen and potassium of tomatoes grown in sand culture

The effects of different rates of application of nitrogen (N) and potassium (K) on several parameters of growth and development were investigated in plants of the determinate tomato cultivar Sunny grown in sand culture. Parameters included fruit set, yield of fresh fruit, fruit firmness, yield of dry matter and nutrient accumulation. Three levels of N applied until first fruit set and three levels of N applied after first fruit set were compared in the presence of two levels of K in a factorial experiment. The soil solution concentrations of N were N/5, N/1 and 2N (N/1 = 8.07 mM N as NO3-) and the K concentrations were K/5 and K/1 (W1 = 3.26 mM K+). The treatments were supplied in a complete nutrient solution every two days. Low N increased the time to fruit set, reduced dry matter yield in leaf, stem, roots and fruit and fresh fruit yield. A reduction in all yield parameters was recorded, irrespective of whether N was low during the pre- or post-fruit set period. Low K and doubling the standard N level had no effect on any fruit set or yield variables. These treatments had no effect on the time from transplanting to fruit maturity or on the temporal spread of harvest. A combination of the lowest N and K levels produced the softest fruit while the highest N and K combination produced the firmest fruit. High levels of N increased the concentration of N in leaf, stem and fruit and the magnesium (Mg) concentration in leaf and fruit but reduced the K concentration in fruit.