Study on the use of source-sink-reserves relations to manipulate grapevine nitrogen use efficiency, aroma and grape maturity and its relationship to yields and wine composition

Canopy management and fruit load control aim to keep a balance between vine’s sources and sinks. In fact, balanced vines may produce more consistent yields and have a more even ripening. This study aims to study the relationship between source–sink ratios and important parameters for production logistics and grape quality, such as progress of ripening and grape composition at harvest. After homogenizing all vines by removing laterals and adjusting the number of shoots to 20, we tested three levels of canopy density and fruit load combined in a factorial design (3 by 3). This is, 3 canopy levels, 100%, 66% and 33% of the leaves combined with 3 fruit loads, 100%, 66% and 33% of the fruit corresponding to 30, 20 and 10 clusters per vine, respectively. Carbon fixation rates were transiently higher in plants with a 33% of the canopy mediated by higher chlorophyll content, although this did not compensate for their smaller leaf area. Onset of ripening was sequentially delayed in 66% and 33% canopy treatments. The progress of ripening, accumulation of soluble solids and loss of acidity (increase in pH and decrease in total acidity), also occurred slower in 66% and 33% canopy treatments compared to 100% of the canopy. In fact, the time to reach commercial maturity (>25°Brix) was delayed 6 weeks for the 33% canopy level. Surprisingly, fruit load did not have a significant effect on the progress of ripening. When comparing all treatments at commercial maturity, the treatment maintaining 100% of the canopy had the highest total acidity and lowest pH. Contrarily, Anthocyanin content was slightly lower in this treatment. These results provide the basis for the control of the speed of ripening, aiming to coalesce variability within a vineyard or optimize the tank capacity through sequential ripening.
Fruit thinning is an important cultural practice in a premium vineyard as it directly affects yields. From fruit set through veraison, wine (especially red) grape growers can remove up to 2/3 of the initial crop borne by the plant at fruit set. This practice is performed aiming for a vine balance between leaf area (sources) and fruit load (sinks). A vine with a higher leaf area-to-fruit ratio (LA/F) is able to ripen (increase °Brix) the crop faster (Kliewer and Dokoozlian 2005; Parker et al. 2014), and presumably, achieve better quality. Contrarily, when there is too much fruit for a given leaf area, ripening (increase in °Brix) can be slower and even stop when is pushed into late October. Under normal circumstances, grape berry accumulates sugars and anthocyanins, while losing astringency (mainly proanthocyanins) and green aromas throughout ripening. Therefore, lack of ripening can be assessed as a slower accumulation of TSS and anthocyanins or retaining high amounts of proanthocyanidins and green aroma compounds. It is well understood that although a balanced wine is the target, there is greater penalization for under ripe wine characteristics than over ripe (Bindon et al. 2014), and in poor sugar accumulation is intimately related to vintage failure (Jones and Davis 2000). Therefore, there is a risk associated with carrying more crop in the grapevine as this can result in an insufficient ripening and quality loss. As grape price or wine retail price is a greater multiplier of revenue than yield in wine grape, dropping fruit is always the decision taken by premium wine grape growers. In addition, when there is a contract between grape growers and wineries, there are great economic interest plead for or against fruit thinning, without any certainty of the true pros and cons of fruit thinning. Given the stability of
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summer weather in California, a better understanding of how source-sink-reserves affect plant fitness, growers could reduce the amount of fruit that they need to drop and still safely achieve an adequate ripening.
Nitrogen applications are a delicate matter as in their deficiency may result into poor growth and in excess may inhibit the production of grape anthocyanins (Soubeyrand et al. 2014). This study aims to determine the impact of nitrogen use efficiency and make recommendations about the application of nitrogen in combination with canopy and fruit load management decisions. Nitrogen is the most frequently deficient nutrient in vineyards, and thus the most often supplemented by fertilizers. Grapevines lose approximately 2.76 lbs of N per ton of grapes harvested, and this value serves as an indication of the minimum amount of N that should be replenished annually. However, that value is an estimate based on the average of data from several studies showing a range from 4.2 to 1.8 lbs of N per ton of grapes (see references in Mullins et al., (1992)). In addition, a great amount of nitrogen is invested in the growth of trunk, roots, leaves and shoots. Although a fraction of this nitrogen is reabsorbed into permanent structures when plants go dormant, a significant amount is lost with leaf fall and dormant pruning, leading to additional demand. Given the significant storage of nitrogen perennial crops in permanent structures, the use of a fertilizer containing labeled nitrogen (15N) allows an estimation of the fertilizer use efficiency, and therefore, determine if the amount of nitrogen prescribed needs to be modified according to cultural practices canopy or crop load management.

The Impacts of Cluster-Thinning and Cluster-Zone Leaf Removal on the Hormone Content of Pinot Noir Grape Berries

During the third year, we confirmed that the relative developmental stage of a berry was not fully a function of the flowering time, but was more associated with seed development. Therefore, our study reinforced the use of a new seed index (SI), also named SB or seed weight-to berry weight ratio to describe berry developmental stage. We have identified and optimized a selection method for selecting individual fruits of cluster at discrete stages using multivariate statistical tools in order to minimize inherent biological variability existing within a grape cluster. The analysis of bioactive forms of auxin, abscisic acid, cytokinin, brassinosteroid, gibberellin, jasmonic acid, and salicylic acid revealed a clear spatial and temporal distribution for most of them during the major critical steps of berry development.

Indeed, we were able to correlate the accumulation dynamics of most of them with major physiological events occurring during berry development. We were also successful in quantifying the effects of two common viticulture practices, cluster-thinning and cluster-zone leaf removal, on two major plant hormones responsible for the ripening initiation (ABA and Auxin). The analysis of the conjugate forms, precursors of, and catabolites of those bioactive analytes revealed specific regulatory pathways. These observations will lead to develop new working hypothesis to explain their mode of regulation in a tissue and developmental context. Based on our results, we will investigate in a near future other layers of biological information including gene expression. Encouraging results during the second year showing a peak ethylene during the ripening will need further investigation in order to prove the real contribution of endogenous ethylene production during grape berry development. From this study, we expect to have at least two peer-reviewed papers published as a result of this funded research and we will propose the results for oral presentation at the next conference of the American Society of Enology and Viticulture.

Interactive Effects of Mechanical Leaf Removal Timing and Regulated Deficit Irrigation on Biosynthesis of Methoxypyrazines and Phenolics on a Procumbent Grapevine (Vitis vinifera cv. Merlot) in the San Joaquin Valley of California

An experiment was conducted in the San Joaquin Valley of California on Merlot to determine the interaction of mechanical leaf removal (control, pre-bloom, post-fruit set) and applied water amounts [sustained deficit irrigation (SDI) at (0.8) and regulated deficit irrigation (RDI) at 0.8 (bud break-fruit set) – 0.5 (fruit set-veraison) – 0.8 (veraison-leaf fall) of estimated vineyard evapotranspiration (ETc) on productivity and berry skin anthocyanin content, composition and its unit cost per hectare.  The pre-bloom leaf removal treatment 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 the post-fruit set leaf removal treatment reduced berry skin mass. The pre-bloom treatment did not affect yield in either year.  Exposed leaf area and leaf area to fruit ratio (m2/kg) were reduced with leaf removal treatments.  The RDI treatment consistently advanced Brix in juice.  Anthocyanin concentration was improved with pre-bloom leaf removal in both years while irrigation treatments had no effect.  Proportion of acylated and hydroxylated anthocyanins were not affected by leaf removal treatments.  In both years SDI increased di-hydroxylated anthocyanins while RDI increased tri-hydroxylated anthocyanins.  Pre-bloom leaf removal when combined with RDI maximized total skin anthocyanins (TSA) per hectare while no leaf removal and SDI produced the least. The cost to produce one unit of TSA was reduced 35%with the combination of pre-bloom leaf removal and RDI treatments when compared to no leaf removal and SDI.  This study provides information to red wine grape growers in warm regions on how to manage fruit to enhance anthocyanin concentration and proportion of anthocyanin hydroxylation while reducing input costs through mechanization and reduced irrigation.

The majority of wine grapes grown in the San Joaquin Valley (SJV) of California are used for bulk wine production.  Fruit used to make red wines from this region are characterized by low anthocyanin accumulation, and receive the lowest price per ton compared to other growing regions in the state. Approximately 34%of the Merlot grapes crushed in the state were grown in the SJV with an average grower return of $ 443/ton compared to $753/ton state average (Cal. Dept. Food. Agric. 2013).  In recent years more efforts have been directed towards applying principles of canopy management with the aid of vineyard mechanization and deficit irrigation practices (Kurtural et al. 2013; Terry and Kurtural 2011; Wessner and Kurtural 2013; Williams et al. 2012) to improve berry composition and grower returns per ton through enhancing the color profile of red wine grapes grown in the region.

Anthocyanins are synthesized via the flavonoid pathway in grapevine cultivars that harbor the wild-type VvmybA1 transcription factor for the expression of UDP-glucose:flavonoid 3-O-glucosyltransferase (UFGT) (Kobayashi et al. 2004).  The encoded enzyme UFGT catalyzes the glycosylation of unstable anthocyanidin aglycones into pigmented anthocyanins.  Two primary anthocyanins (cyanidin, delphinidin) are synthesized in the cytosol of the berry epidermis.  Cyanidin has a B-ring, di-hydroxylated at the 3’ and 4’ positions and delphinidin has a tri-hydroxylated B-ring because of an additional hydroxyl group at the 5’ position.  Flavonoid precursors are initially recruited from the phenylpropanoid pathway by chalcone synthases (CHS1, CHS2, and CHS3) and enter the flavonoid pathway.  Two parallel pathways downstream of flavonoid 3’-hydroxylase (F3’H) and flavonoid 3’,5’-hydroxylase (F3’5’H) (Castellarin et al. 2007) produce either cyanidin or delphinidin.  The 3’ position of cyanidin and delphinidin and sequentially the 5’ position of delphinidin are methoxylated by o-methyl-transferase (OMT) that generates peonidin, petunidin and malvidin, respectively (Castellarin et al. 2007).

The concentration and relative abundance of single and total anthocyanins are variable among red winegrape cultivars due to genetic control and developmental regulation.  However, there is general agreement in literature that when amount of diffuse light is increased (Dokoozlian and Kliewer 1995) or when an amelioration of microclimate temperature is associated with a concomitant increase in diffuse light quantity (Spayd et al. 2002), beneficial effects on total skin anthocyanin content of red wine grapes grown in hot climates are observed. Conversely, exposure of clusters to direct sunlight (Berqvist et al. 2001) or low sunlight with concomitant increase in berry temperature (Tarara et al. 2008) was shown to decrease anthocyanin accumulation, increase the proportion of 3’4’ hydroxylated anthocyanidins, and decrease the acylated anthocyanins contributing to total skin anthocyanins.  Cortell and Kennedy (2006) also reported a reduction of tri-hydroxylated anthocyanins in shade grown Pinot noir.  Therefore, the effect of sun exposure results from the interaction of several factors that are hardly uncoupled under vineyard conditions.

Leaf removal is a practice that can improve light transmittance into fruiting zone of the canopy (Diago et al. 2012; Poni et al. 2006; Wessner and Kurtural 2013; Williams 2012).  When leaf removal was applied pre-bloom it was shown to decrease berry set and hence grapevine yield, but improved total skin anthocyanin concentration of red wine grapes (Diago et al. 2012).  The results were used as a means of crop control with the increase in relative skin mass and reduction in yield per cluster being interpreted as the causal increase in anthocyanin concentration.  Therefore, since growers in SJV are paid in tons produced per hectare, previous work in the hot climate of SJV focused on post-fruit set, but was conducted pre-veraison in order to not adversely affect yield (Wessner and Kurtural 2013; Williams 2012). The leaf removal studies conducted in SJV resulted in improved photosynthetically active radiation exposure to canopy interior but no physiological gain for the cultivars studied, some deleterious effects were noted due to overexposure of clusters to direct solar radiation or vegetative compensation response (Geller and Kurtural 2012; Kurtural et al. 2013; Williams 2012).Water deficits were shown to consistently promote higher concentrations of anthocyanins in red wine grapes (Kennedy et al. 2002; Romero et al. 2010; Terry and Kurtural 2011).  However, there were conflicting results as to whether or not there were any direct effects on berry metabolism other than inhibition of berry growth.  It remained unclear if water deficits altered the biosynthetic pathway or if high anthocyanin concentrations resulted from elevated sensitivity of berry growth to water deficits.  Matthews and Anderson (1989) reported that growth of berries was inhibited more and concentrations of anthocyanin in berry skin and wine increased when water deficits were imposed before veraison rather than after veraison.  Similarly, Terry and Kurtural (2011) reported water deficits imposed one-week post-fruit set until veraison resulted in a 25%amelioration of total skin anthocyanins in central SJV.  Based on the observation of similar anthocyanin content per berry, Kennedy et al. (2002) and Terry and Kurtural (2011) concluded that post-veraison water deficits only inhibited fruit growth.

Gene expression studies investigating the regulation of anthocyanin biosynthesis in the grapevine concluded that both pre and post-veraison water deficits increased anthocyanin accumulation.  What is more, water deficits can progressively modify the canopy microclimate by defoliating the basal leaves subtending the fruiting zone, with greater exposure to solar radiation (Terry and Kurtural 2011; Williams 2012).  However, the increase in anthocyanin concentration observed in Merlot grapevines exposed to water deficits was determined not to be due to basal leaf defoliation and exposed solar radiation but was the direct result of water deficit.  Castellarin et al. (2007) reported that the increase in anthocyanin concentration in Merlot was not due to overexpression of FLS1 gene that is strongly correlated with cluster light exposure for flavonoid biosynthesis in the grapevine, but was due to up-regulation of flavonoid synthesis genes, in particular UFGT, CHS2, CHS3, and F3H.While canopy and crop load management studies (Geller and Kurtural 2012, Kurtural 2013; Terry and Kurtural 2011, Wessner and Kurtural 2013) and irrigation studies, particularly those implementing deficit irrigation, have been conducted in the coastal grape growing regions of California (Matthews and Anderson 1988; Williams 2010; 2014), no such studies have combined both factors on wine grapes cultivated in the hot climate of the SJV of California. The overachieving objective of this trial was to quantitatively increase the concentration of total skin anthocyanins of Merlot by investigating the interactive effects of manipulating solar radiation and water amounts applied in this hot climate. The specific objectives of the trial were to improve the light microclimate without adversely affecting yield components while simultaneously reducing applied water amounts to quantitatively and qualitatively improve the skin anthocyanin composition of Merlot in a resource limited environment.

The experiment was a three (leaf removal) × two (deficit irrigation) factorial with a split-plot design with four replicated blocks.  Three rows of 190 vines each comprised one block and four guard rows separated each block.  The three leaf removal treatments were randomly applied as main plot to three rows each.  Each main plot of three rows was split into two deficit irrigation treatments as sub-plot at random, in the geographic middle on the East-West axis of the vineyard.  Each experimental unit consisted of 285 vines of which 48 were sampled from an equi-distant grid per treatment-replicate.

 

 

 

 

Vineyard Air Temperature Profiles and Their Implications for Vine Training Decisions

This project evaluated how air temperatures vary with height above the ground surface throughout the growing season at various vineyard areas representative of the diverse Central Coast region. The purpose of this project was to identify if useful stratification in temperatures occurred at the study sites, and to quantify the potential benefits that could be attained by using alternative vine training heights to reduce potential frost risk and/or to avoid excessive summertime temperatures. The fundamental hypothesis of this effort has been that taller vine training heights may bring useful benefits in some areas, and that this type of detailed temperature analysis will help identify those areas and help to predict what benefits may be obtained with any changes in vine training height.

The 2013 season measurements at seven sites in San Luis Obispo and Santa Barbara Counties proceeded as planned, however with an equipment malfunction resulting in only partial season data at one site in Shandon. Temperatures were measured at one-foot intervals above the ground surface between 1 ft. and 8 ft. heights, using precision data loggers taking high-frequency measurements. Some sites demonstrated useful increases in temperature with increasing height above the ground surface on cold spring nights, but this pattern was not observed everywhere. In the most extreme example, the temperature gain at 8 ft. elevation was 9 °F warmer than at 1 ft. elevation; such stratification would have very positive benefits for frost protection. Other sites showed little similar stratification, likely due to air movement during the night.

At all sites the cumulative degree days over the April 1 – October 31 growing period tended to decrease with increasing height above the ground. This indicates the potential that taller vine training heights may have for addressing some of the gradual increases in degree days that have been occurring in recent decades, and which are forecast to continue increasing with climate change.

In 2014, detailed measurements are being conducted with multiple stations at two properties, to determine how variable the temperature profile characteristics can be at individual sites. The assessment of temperature profiles over different ground cover conditions was not conducted as planned due to insufficient cover crop conditions; this will be addressed at a later date.

Evaluating the Role of Excess Levels of Nitrogenous Compounds, Including Amino Acids and Putrescine, in the Occurrence of Pinot Leaf Curl

The objectives to investigate the relationship between elevated ammonium and glutamine levels in grape leaves exhibiting Pinot Leaf Curl and to compare the levels of putrescine in symptomatic and asymptomatic leaves were completed.  Ammonium and glutamine varied widely among leaf samples and in many instances leaves with symptoms showed elevated levels of these metabolites compared to leaves without symptoms. However, examples where the levels of glutamine and ammonia were nearly equal were found and in some cases symptom leaves actually exhibited lower levels of these compounds than non-symptom leaves.

While the levels of ammonia and glutamine are certainly of interest in assessing the nitrogen status of grapevine leaves, they do not show promise as markers or indicators of Pinot Leaf Curl. On the other hand, the diamine putrescine (1,4-diaminobutane) was found to be elevated in 12 of 14 cases studied in this project, and in the other two the levels were the same in symptom and non-symptom leaves. Therefore, unlike glutamine and ammonia, no examples were found where putrescine was higher in non-symptom leaves than in symptom leaves.

Since putrescine has been implicated as a toxic metabolite leading to leaf chlorosis and necrosis in potassium deficiency and Spring Fever this research suggests the possibility that it also plays a role in Pinot Leaf Curl. However, given the range of putrescine observed in symptom and non-symptom leaves from various Pinot varieties and clones from different sites, its presence remains correlative relative to symptoms and a causal role remains to be established.

The success of this research lies in the fact that prior to this study we had only anecdotal evidence that Pinot Leaf Curl is a nitrogen-related disorder. The differences seen in all of the nitrogen metabolites studied in this project, especially putrescine, give some support to that idea and may suggest management practices that could be tried in an attempt to ameliorate the disorder.

Interactive Effects of Mechanical Canopy Management and Reduced Deficit Irrigation on Shiraz Grapevines

Canopy microclimate of Shiraz/1103P grapevines were altered and exposed to Reduced Deficit Irrigation (RDI) with varying severity and timing. Four canopy levels were imposed by dormant pruning the vines to 42 spurs (control), mechanically pruning others to 4? hedges and mechanically thinning shoot and cluster density to 5 shoots/foot of row , 9 clusters/foot (CLL); 7 shoots/foot, 15 clusters/foot (CLM); and 16 shoots/foot , 17 clusters/foot (CLH), respectively. Control vines were irrigated to 70% of Et until harvest (RDIC). Other vines either received 70% of full vine Et until to veraison, after which the rate was cut to 50%of Et (RDIL) or had their irrigation cut to 50%of Et before veraison (RDIE), but not thereafter. At veraison, the shoots exposed per hectare were 53%and 39%lower for the CLL, and CLM; but 43%higher for the CLH when compared to Control. The distance between shoots was 137%and 81%higher for the CLL and CLM, but 29%lower for the CLH compared to Control. Compared to control, the leaf layer number was 55% and 50% lower for the CLL and CLM, but 20%higher for the CLH. The RDIE and RDIL treatments lowered the leaf layer number by 22%and 10%, respectively compared to RDIC. Berry weight was 2%, 5%, and 11% lowered by the CLL, CLM, and CLH, respectively. RDIE also reduced berry weight by 16%at harvest compared to RDIC and RDIL. Yield was reduced by 33%, 29%by the CLL and RDIE, but increased by 5% and 17% for the CLM and CLH, respectively. The CLL and CLM reduced the leaf area to fruit ratio by 33%, and 54%respectively whereas the RDI treatments did not affect the leaf area to fruit ratio. There was an interaction of canopy management and RDI stress on wine total phenols, tannins, and anthocyanins whereas the CLM with RDIL had the highest tannins and total phenolics. The highest wine anthocyanins were seen with the CLM with the RDIE. This study provides important information for growers considering mechanizing canopy management operations while scheduling reduced deficit irrigation, where best results were achieved with a combination of CLM and RDIE treatments. That translates into 7 shoots per foot of row after mechanical shoot thinning, 15 clusters per foot of row after cluster thinning concurrent with shoot thinning resulting in 3 to 4 leaf layers with shoots 2 inches apart along the cordon, yielding 9.2 to 10 tons/acre with berry size reduced by 5% on shorter rachises, and 420 mg/L malvidin-3-glycoside eq, 1045 mg/L CE of total phenols, 165 mg/L CE of tannins and 873 mg/L CE of non-tannin phenols in wine.

Sustaining Bud Fruitfulness, Yield and Wine Composition of Pinot Grigio and Shiraz in Southern San Joaquin Valley

Canopy microclimate of Syrah06/SO4 was altered through application of three dormant pruning, and two leaf thinning treatments arranged factorially in four randomized complete blocks to investigate how to rejuvenate vineyards with declining productivity. Vines were either pruned by hand to 22 nodes, or mechanically box-pruned to a 10 cm hedge, or cane- pruned by hand to six, 8 node canes arranged in opposing directions of the row with horizontal canopy separation, and leaves were removed on the east side of the canopy in the fruit zone, or not. Percent photosynthetic photon flux density (%PPFD) transmittance of mechanically box-pruned vines was 34%and 38%greater than spur or cane-pruned vines, respectively. Leaf removal increased %PPFD by 47% compared to control. Canopy separation decreased cluster and berry weight, while increasing cluster number and yield per vine. Canopy separation delayed harvest by one week, while retaining lower juice pH and higher total acidity. Berry weight of spur-pruned vines was 15% greater than other pruning methods. Cluster number was 37% higher on cane-pruned vines with canopy separation compared to mechanically box-pruned vines, which were 22% higher than spur-pruned vines. Berry skin total phenolics at harvest of cane-pruned vines was 11%greater than spur-pruned vines, which was 8% greater than mechanically box-pruned vines. Pruning method and leaf removal interacted to affect the total iron reactive phenolics and tannin concentration in resultant wine. Crop load of cane-pruned vines was 43% and 32% greater than spur-pruned and mechanically box-pruned vines, respectively. The results from this study provide information for largescale growers on how to rejuvenate vines that have declined in productivity. Canopy microclimate of Syrah06/SO4 was altered through application of two dormant pruning, three shoot thinning, and two leaf thinning treatments arranged factorially in four randomized complete blocks to mitigate crop load. Vines were spur-pruned to 22 nodes or mechanically box-pruned to a 10 cm hedge, shoot thinned to 23 shoots/m of row (low), 32 shoots/m of row (medium), or 49 shoots/m of row (high), and leaves were removed on the east side of the canopy within a 45 cm zone of the fruit zone, or not. The cluster number (p<0.0001), leaf area to fruit ratio (m2/kg) (p<0.0115), shoots exposed per acre (p<0.0111), and yield (p<0.0001) increased linearly with the increase in crop load, while the pruning weight per vine (p<0.0001), berry weight at harvest (g) (p<0.0222), cluster weight (g) (p<0.0011), increased with the decrease in crop load. Leaf layer number of the Syrah canopies were better predictors of berry skin anthocyanins (p<0.0285), and tannins (p<0.0166) when compared to crop load (p<0.1435 and p<0.3721, respectively). The most preferable fruit at the farm gate was achieved with 65,000 shoots exposed per hectare, that were 5.0 cm apart along the cordon, with 3.2 leaf layers resulting in 20.5 tons per hectare yield when harvested at 24% total soluble solids. This study provides information for growers who aim to balance vine growth with fruit and quality through on-site measurements for mechanically managed vineyards in the southern San Joaquin Valley of California. To better understand the optimal canopy management techniques necessary to meet the demands of both vineyard and cellar, a study was conducted analyzing the interactions amongst canopy management steps for Pinot Grigio in the southern San Joaquin Valley. The treatments were arranged factorially where two pruning methods (spur vs. mechanical box-pruning), three shoot density levels (low (23 shoots/m), medium (33 shoots/m), high (49 shoots/m)), and two leaf removal methods (east-side leaf removal, or none) were applied to alter the canopy microclimate in four randomized complete blocks. Pruning method and shoot density interacted to affect the count shoots and total shoots retained per meter of row. Canopy microclimate was affected by pruning method, shoot density, and leaf removal treatments. Light interception into the fruiting zone was 49% higher for spur pruned vines compared to mechanically boxpruned, and was 44% higher for low shoot density compared to high shoot density treatments. A 17% decrease in leaf layer number was observed for vines with leaf removal. Yield was impacted by both dormant pruning and shoot thinning methods where an increase of 42% in mechanically box-pruned vines was seen compared to spur pruned, and increase of 27% from low to high shoot density. Crop load and vine vigor was impacted by the interaction of shoot density and leaf removal. Leaf area to fruit weight ratio reached the desired range (0.8-1.2 m2/kg) for medium shoot density treated vines that were mechanically box-pruned. Wine phenolics analysis indicated a three way interaction amongst pruning method, shoot density, and leaf removal indicating quantitative wine parameters were multi dependent on canopy management methods.

Interactive Effects of Mechanical Canopy Management and Regulated Deficit Irrigation on Shiraz Grapevines

Canopy microclimate of Shiraz 06/1103P grapevines were altered and exposed to Regulated Deficit Irrigation (RDI) with varying severity and timing to mitigate the crop load. Four crop load levels were imposed by dormant pruning the vines to 22 spurs (control) with no further manipulation, and mechanically pruning others to 4? hedges and mechanically thinning the canopy to a density of 7 count shoots/foot of row (CLL); 9 count shoots/foot of row (CLM); and mechanically box pruning to a 4-inch hedge with no shoot thinning (CLH), respectively. Control vines were irrigated to 70%of ET until harvest (RDIC). Other vines either received 70%of full vine ET until to veraison, after which the rate was cut to 50%of ET (RDIL) or had their irrigation cut to 50%of ET before veraison (RDIE), but not thereafter. Application of shoot thinning at Stage 17 of the E-L scale by removing 25%of the total shoots exposed with the CLM resulted in exposing about 32000 shoots per acre with count shoots spaced about 2? along the cordon. This exposure translated to about 4 leaf layers and about 13 m2 of leaf area to ripen the clusters retained on the vines. The leaf area to fruit ratio achieved with the CLM treatment exposes just enough leaf area to ripen the crop level retained on the vines. The combination of the CLM and RDIE treatments decreased the berry weight harvest by 12%without any decrease in harvest weight compared to hand-pruned control resulting ~ 10 tons/acre yield in 2010. The resultant crop harvested from this treatment combination was harvested 4 days later than the hand-pruned control irrigated with RDIC. The combination of CLM with RDIE resulted in wines with higher total iron-reactive phenolics (1510 mg/L CE eq.), higher tannin concentration (520 mg/L) and similar anthocyanin concentration (250 mg/L CE eq.) to hand-pruned control with RDIC. This project at the end of its second year provides valuable information to growers by indicating dormant pruning and shoot thinning can be done efficiently and precisely with mechanization while saving irrigation resources. The identified treatment combinations (CLM with RDIE) results in smaller berry size without adversely affecting yield with preferable wine phenolic composition in the San Joaquin Valley of California.

Impacts of Early Season Fruit Zone Leaf Removal on Disease Control, Fruit Set, Vine Growth and Grape and Wine Quality of Pinot Noir

Early season leaf removal in the cluster zone can be used as a tool in integrated pest management. The practice of leaf removal is typically conducted in the vineyard after fruit set but before véraison to increase sunlight penetration for fruit development and to enhance fruit quality. Leaf removal at developmental stages prior to bloom may be beneficial in increasing spray penetration for disease control within the grape inflorescence and may also lead to increased fruit quality with increased phenolic precursor production. The study investigates leaf pulling at various growth stages, including flower separation, bloom (50%cap fall), fruit set, pea?sized berries, bunch close, and no leaf pulling. The 2010 season of this study indicates that there is a benefit to leaf pulling early in the season to increase spray penetration of fungicide and to help alter the microclimate to create an environment that is not conducive to Botrytis or powdery mildew infestation. Leaf removal that occurs prior to bunch closure helped reduce disease incidence and severity more than the no leaf pull control. There was a nearly 20 percent reduction in fruit set in pre-bloom treatments at both sites in 2010. This resulted in differences in cluster architecture, including berries per cluster and cluster weight. There were no observed differences in berry weight. Differences in berries per cluster could potentially have acted to reduce disease infection in clusters. This was the first season of this trial where basal leaf removal employed early in the season reduced fruit set. Leaf pulling in the entire cluster zone has not delayed fruit ripening nor total anthocyanins or phenolics. There was no fruit sun-burning observed in any of the leaf pull treatments for the duration of the study despite complete exposure of clusters from pre-bloom though harvest. Continued research into this trial is required to determine the impact of early season leaf removal on disease incidence and secondary effects on fruit quality.

Alternative Trellising Systems for Chardonnay and Merlot Vineyards in the Central Coast

A four-year study (1998-2001) compared the long-term performance of bilateral cordon trained, spur pruned Chardonnay and Merlot grapevines trellised to the vertically shoot positioned trellis system (VSP), the vertically divided Smart-Henry trellis system (SH) and the vertically separated Smart-Dyson trellis system (SD). Vine vigor at the site was moderate. Compared to the VSP, the SH and SD systems reduced canopy density and improved fruit zone microclimate. SD and SH vines had fewer leaf layer numbers and greater amounts of sunlight in their fruiting zones compared to VSP vines. Primary, lateral and total leaf areas per vine were similar among the treatments, indicating that differences in canopy density were a result of canopy division or separation along with an increase in total canopy volume available for foliage distribution. Over the course of the study the yield of SH and SD vines was generally10%to 15%greater compared to VSP vines. Pruning weight per vine and the yield:pruning weight ratios were generally similar among the treatments in both cultivars. In the first year of evaluation fruit on downward-oriented shoots on the SH system ripened more slowly compared to shoots oriented upward, but these differences diminished as the yield of the lower fruiting zone in this system declined. No significant difference in fruit ripening was observed due to shoot orientation in the SD. Few differences in combined fruit (upper and lower canopies) soluble solids, titratable acidity and pH were observed among the treatments in either cultivar over the four-year period. Fruit and wine color (Merlot) were improved in the SD and SH treatments, and wines from these treatments in the Merlot were preferred over the VSP system in three of the four years of the experiment. We found that SD and SH trellis systems significantly improved both yield and fruit composition compared to the VSP system. SD is preferred over SH based on ease of establishment and culture, as well as long-term productivity; both vigor and productivity of downward trained shoots in the SH declined over the course of the study.

PDF: Alternative Trellising Systems for Chardonnay and Merlot Vineyards in the Central Coast