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2010 Research Report Michigan Grape & Wine Industry Council

Proposal Title: EARLY LEAF REMOVAL TO IMPROVE CROP CONTROL, CLUSTER MORPHOLOGY AND BERRY QUALITY IN VINIFERA GRAPES. Principal Investigator: Name: Paolo Sabbatini E-mail: sabbatin@msu.edu Mail Address: A 20 Plant and Soil Science East Lansing MI, 48824 Telephone: 517-5191 x 302 Fax: 517-353-0890 Abstract

The effect early leaf removal treatments was investigated on Chardonnay and Pinot Noir (clones UDC 4 and UDC 9) at the SWMREC during 2010. Leaf pulling treatments were manually applied during pre-bloom, at full bloom and at fruit set in each variety. The treatments consisted in a defoliation of the first six nodes of all the shoots. Fruit set was estimated following the treatments, and canopy development (leaf area) was measured until pea-size growth stage. Berry skin characteristics were studied after veraison and on samples collected at harvest, while cluster architecture and basic fruit chemistry parameters, as well as yield data were measured at harvest. 1 – Introduction and Priority Addressed:

Crop control is a priority in many viticultural areas of the world to assure high quality wines, and it is traditionally achieved with winter pruning, node count adjustment, and, for further fine-tuning, manual shoot and cluster thinning. Leaf removal in the fruiting zone frequently is performed from fruit-set to veraison in several cool grape growing regions (Reynolds et al., 19961) to improve light exposure, and temperature of the cluster with beneficial effects on berry quality and color. Vine growth is functionally associated to the balance between vegetative and reproductive organs, and carbohydrate source availability at pre-anthesis is strictly related to yield influencing annual fruit set (Caspari and Lang, 19962). Recent trials reported that manual defoliation near the time of bloom is effective in reducing yield, because affecting fruit set (Sabbatini et al, 20103, Sabbatini

1 Reynolds A.G., Wardle D.A, Naylor A.P., 1996. Impact of training system, vine spacing, and basal leaf removal on Riesling. Vine performance, berry composition, canopy microclimate, and vineyard labor requirements. Amer. J.Enol Vit. 47: 63-76. 2 Caspari H.W. and Lang A., 1996. Carbohydrate supply limits fruit set in commercial Sauvignon Blanc grapevines. Proc. 4th Intern. Cool Climate Vit. Symposium, II, 9-13. 3 Sabbatini P., Howell G.S., Wolpert J., 2010. Controlled Cultural Reduction in Fruit Set and Subsequent Harvest Season Botrytis Cluster Rot Complex. Italus Hortus, pp 27-32.

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and Howell, 20104) and berry size, and leading to looser clusters with improved must composition (Intrieri et al., 20085).

2 - Original goals and objectives of the project:

The proposed goal of this project was to verify whether early leaf removal (pre-bloom, full-bloom and fruit set) can be consistently used as a tool for controlling yield through reduction of fruit-set in highly productive Vitis vinifera cultivars characterized by compact clusters, such as Pinot Noir and Chardonnay. Previous research funded by the MGWIC and recently published (Sabbatini and Howell, 20104) showed the efficacy on early leaf removal in modifying the cluster architecture in several hybrids cultivars and the efficacy in controlling bunch rot in cultivars prone to this devastating disease in cool–humid viticultural regions. The research reported in this document was initiated to investigate:

1. The effect of early leaf removal on fruit set and yield per vine 2. Whether the expected yield reduction is primarily derived from reduced fruit-set

and/or reduced berry size 3. The effects of leaf removal on grape quality (fruit chemistry and skin/pulp ratio); 4. The effect of the treatments on cluster morphology and on bunch rot incidence. 5. The potential effect of early leaf removal on bud fruitfulness (year-2 carry-over

effect); Project Period: January 2010 to July 30, 2011. 3 - Work accomplished during the period, including material and methods and results:

Two clones of Pinot Noir (UDC 9 and UDC 4) and Chardonnay trained at VSP were pruned during the winter of 2010 up to 60 buds/vine and subsequently thinned to a more balanced crop level per vine for high quality grape production, similar to industry standards. The vines were grown at SWMREC (Benton Harbor, MI) during the summer 2010. A leaf removal treatment was applied at three different stage of shoot development during the early season. Six nodes per shoot were defoliated removing whole leaves at three stages of cluster development: before bloom, full bloom and fruit set (stage 17, 23 and 27 according to Eichorn and Lorenz). In Pinot Noir, both vegetative and reproductive growth were slightly more advanced than Chardonnay at the time of defoliations. Control treatment was also included in the experiment, with no leaf removal performed. On each experimental vine, five shoots bearing two clusters were selected and tagged at the beginning of the experiment: shoot length was measured at each time of defoliation, and two weeks after the last defoliation treatment. The impact of leaf removal on vines leaf area was estimated at each time of defoliation on 20 homogeneous shoots sampled in the same experimental plot: leaf area (LA) removed, total LA and shoot length was measured. The average LA removed used to estimate the impact of leaf area removed on treated vines, and the regression between shoot length and total LA was used to estimate LA of the defoliated shoots (Table 1).

4 Sabbatini P. and Howell G.S., 2010. Effects of early defoliation on yield, fruit composition and harvest season cluster rot complex of grapevines. Hortscience, Vol 45 (12); pp 1804-1808. 5 Intrieri C., Filippetti I., Allegro G., Centinari M., Poni S. 2008. Early defoliation (hand versus mechanical) for improved crop control and grape composition in Sangiovese (Vitis vinifera L.). Austr. J. Grape and Wine Res. 14, 25-32.

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The impact of defoliation time on vegetative growth is shown in Table 1. Defoliation treatments were more severe, in terms of LA removed, at subsequent shoot development stages in Chardonnay. Nonetheless in Pinot Noir, the LA removed was not significantly different at full bloom and fruit set, when possibly the leaf area expansion on the first six nodes targeted for defoliation was already completed. Moreover, in Chardonnay, the defoliation treatment effect persisted later in the season, as we observe from the estimated leaf area, which is lower than the control in all defoliation treatments. However in Pinot Noir the leaf area on the defoliated shoots was not significantly lower than the control, possibly laterals compensated the vegetative growth.

Figure 1. Florets and berries counted on pictures to estimate fruit set.

Table 1. Vegetative measurements on defoliated shoots. Leaf area removed was estimated at each time of defoliation, shoot length and total leaf area were measured two weeks after fruit set.

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To investigate the effect of the defoliation treatment (leaf pulling) on fruit set, each basal inflorescence on the tagged shoots was photographed against a dark background, and visible flowers in the pictures counted (Fig. 1).

The number of actual flowers was then estimate using a regression equation established on the destructive sampling of 20 inflorescences for both Chardonnay and Pinot Noir. The same procedure was repeated at fruit set to estimate the number of berries set per cluster. The regressions obtained from this part of the study are reported on Figure 2. The estimated number of flowers and berries, and fruit set percentage are reported in Table 2.

According to these preliminary data, the fruit set increased when the defoliation was

performed at fruit set. Although this result is questionable and not in harmony with the hypothesis and probably related to physiological coulure, the data is consistent with the number of berries per cluster counted at harvest, confirming that the non-destructive methodology could eventually be used for later studies on fruit set effect. The

Table 2. Estimates of flower and berries number per cluster, fruit set%: data were elaborated from the picture interpretation on Chardonnay basal clusters.

Figure 2. Right: Linear regression between flower numbers and flower visible on pictures taken at full bloom of Chardonnay (white circles) and Pinot Noir (black circles) inflorescences. Regression equations: y=1.50x -15.74, r² = 0.82 (Pinot Noir); y = 1.64x - 11.16, r² = 0.83 (Chardonnay). Left: Linear regression between number of berries and berries visible on pictures taken at fruit set of Chardonnay and Pinot Noir clusters. Regression equations: y = 1.76x - 25.23, r² = 0.71 (Pinot Noir); y = 1.23x - 3.40, r² = 0.92 (Chardonnay).

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methodology was not as effective in Pinot Noir, where differences in the fruit set were not detected with the picture interpretation (data not shown).

At harvest (Sept 12th, 2010) yield per vine was recorded, and clusters from the tagged shoots were separately collected and analyzed in the lab. Weight and number of berries, weight and length of the rachis was recorded per cluster (Table 3).

The number of clusters and total yield per vine was not affected by the leaf removal treatment in both Chardonnay and Pinot Noir (data not shown). Nevertheless, early defoliation (before bloom and at bloom) in Pinot Noir successfully reduced berry weight and number of berries per cluster, leading to a reduced cluster weight. Since the rachis length was not affected by the defoliation treatment, the observed lower cluster compactness of the earliest defoliation treatments is due only to the reduced number of berries per cluster. Indeed, the defoliation treatment at fruit set, did not affect fruit set as well as cluster compactness.

All the defoliation treatments, for both varieties significantly reduced the number of rot berries per cluster, also on clusters with a more usual compact architecture (e.g. fruit set defoliation treatment for Pinot Noir and all defoliation treatments in Chardonnay). Lower level of bunch rot incidence can eventually be ascribed to the improved fruit zone microclimatic conditions, in particular air circulation, and lower humidity, but also to a better penetration of fungicides applications.

Juice from berries collected at harvest was used for basic chemistry analysis (Brix, pH, and TA); subsamples of 60 to 100 g of berries per vine were used to perform total

Table 3. Chardonnay and Pinot Noir cluster measurements and cluster architecture. Data collected at harvest from 5 selected shoots per vine.

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anthocyanin, phenolics and terpenes analysis via spectrophotometer according to Iland et al. (20046). Results for fruit chemistry are reported in Table 4.

The effect of leaf removal and sun exposure of the clusters on grape quality is well documented (Reynolds et al. 19961) However, our results indicates that basic fruit chemistry is not affected by the defoliation, although a significantly lower titrable acidity is observed in Pinot Noir following leaf removal, suggesting a possible effect of cluster exposure in advancing the ripening process. Likely, the extremely favorable and warm 2010 season covered up possible differences in sugar content and in quality indexes for a mid-early ripening variety such as Chardonnay. As expected, all the defoliation treatments increased the phenolics content of berries but did not specifically increase anthocyanin level in Pinot Noir juice or terpenes (responsible for aroma) in Chardonnay.

The effect of defoliation on berry morphology and particularly on berry skin was

studied on berries sampled at harvest. Three berries per cluster were sampled randomly per each tagged shoot of Pinot Noir and Chardonnay vines. The berry samples were individually weighed, diameter measured and then sliced in half with a razor blade. Skin, seeds and flesh were separated and removed using a metal spatula without rupturing pigmented hypodermal cells. Seeds and skin were immersed in distilled water, rinsed and blotted dry with a tissue. Skin and seeds were weighed separately. In Pinot Noir only the earliest defoliation treatment resulted in berries with higher skin weight and skin/berry weight ratio, consistently with information reported in the literature (Poni et al. 20067). This was not observed in Chardonnay. 6 Iland P., Bruer N., Edwards G., Weeks S and Wilkes E., 2004. Chemical anlysis of grapes and wine; techniques and concepts. Patrick Iland Wine Promotions Pty Ltd, Adelaide, Australia. 7Poni. S., Casalini L., Bernizzoni F., Ciavardi S., Intrieri C. 2006. Effects of early defoliation on shoot photosynthesis, yield components, and grape quality. Amer. J. Enol. Vitic. 57, 397-407.

Table 4. Fruit chemistry for Pinot and Chardonnay measured on subsamples at harvest.

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4 - Conclusion Leaf removal at earlier stages of cluster development, at bloom or before bloom, appear to be an effective strategy, at least in Pinot Noir, to control berry size and berry numbers per cluster. Consequently it could be used as a method to achieve smaller cluster and therefore control vine crop load. Defoliation treatments in both Chardonnay and Pinot Noir improved grape quality, reducing the rot incidence at harvest and increasing polyphenols content, as a consequence of both reduced cluster compactness and better fruit zone microclimatic conditions. Investigations on the effect of defoliation on year 2 bud fruitfulness are ongoing. 5 - Communications Activities, Accomplishments, and Impacts: During this first year of the project, Dr. Sabbatini has given numerous talks at grape grower meetings to highlight the preliminary results of this research. This has included the Great Lakes Expo, summer grape IPM meetings in southwest and northwest Michigan, at the 2011 Midwest Grape and Wine Conference (St. Louis, MO, February 4th) ant it will presented in august 2011 at and International Viticulture conference in Europe (accepted as oral). We will develop a manuscript for publication based on this research, and will work towards an extension publication by MSU Extension. The funds provided by the MGWIC are partially covering the cost of a MS student (Dana Acimovic) working full time of this project. Matching funds were secured through the GREEEN project. In 2010 we failed to get more financial support from other agencies (e.g. Viticulture Consortium East). The review of the project was favorable; therefore we are planning for 2011 to submit again this proposal to national funding agencies. We thank Pat Murad, Shijian Zhuang and Letizia Tozzini for fruit analysis and technical assistance with this project, and the farm management staff at SWMREC as well as the Michigan Grape and Wine Industry Council and Project GREEEN for financial support of this study.