ABSTRACT
Cluster management in table grapes is an essential cultural practice for production of high quality table grapes. This issue has not been studied in the Intermountain West region in the United States. Thus, the objective of this project was to study the effects of cluster removal, cluster shortening, and vine girdling on yield and quality attributes of ‘Alborz’ table grape during 2012–14 growing seasons. Vines that did not receive cluster removal and cluster cutting (NoClRemNoClCut) tended to have a higher yield but smaller berry weight than those with other cluster managements every year. Vines receiving cluster removal, cluster shortening, and a trunk girdling (ClRemShort&Gird) regime tended to have larger berries and cluster weight than those with other treatments. However, girdled vines were more susceptible to cold damage. Vines receiving cluster removal and cluster shortening had slightly larger berries, better appearance, and marketability than those without cluster removal and without cluster shortening.
Introduction
Table grapes are one of the most important fruit crops for many regions, and even at a small scale, would fit perfectly in the operation of any wine grape and tree fruit grower in the Intermountain West region of the United States, which includes Washington, Idaho, Utah, Colorado, and Oregon. Table grapes in this region are harvested when most of the fresh table grapes in California are either finished or are only available in storage.
Table grapes can either be grown as a major commercial fruit crop or as an alternative fruit in a new region. As the world population grows and people of different cultural and ethnic backgrounds gather and live in a new region or city, the demand for diversification of fruits and vegetables increases to meet the needs of this new demography. Among all traditional or alternative fruit crops, table grapes are always popular because of their health benefits. Adaptation and production of table grapes beyond California would reduce the cost of transportation and create a niche market (Fallahi et al., Citation2001; Fallahi, Citation2006).
In the United States, various viticultural and berry sensory characteristics are well documented in California where Vitis vinifera is widely grown (Nelson, Citation1985; Nelson et al. Citation1973; Weaver, Citation1976). However, despite the importance of table grapes as an alternative fruit, berry characteristics and cultural practices are less studied in other states, such as Idaho (Fallahi et al., Citation2006; Fallahi et al., Citation1995, Citation2001), Ohio (Cahoon et al., Citation1985), Florida (Mortensen and Balerdi, Citation1974; Mortensen and Harris, Citation1988); and Western Oregon (Hemphill et al., Citation1992).
Grape cluster management is a form of crop thinning that is achieved by a complete removal and/or shortening of the cluster at flower or after fruit set. Crop thinning allows growers to modify vine balance (vegetative growth to fruit ratio). Cluster removal in wine grapes is often practiced in cool wine-growing regions (low heat unit) to reduce the crop and allow certain cultivars with excessive crop to produce sufficient sugar content (Fallahi et al., Citation2008; Skinkis, Citation2017). The intensity of crop thinning is highly dependent on the cultivar, vine health, and climate (Skinkis, Citation2017). Some cultivars may require annual crop thinning to maintain adequate vine strength.
Climatic conditions in the regions where table grapes are produced as a new crop could be significantly different than those areas where this crop has been grown for many years. Fluctuations of temperatures and the length of the frost-free season play extremely important roles in the acclimation and productivity of vines in any region. Thus, similar to the situation of wine production in cool regions, table grape crop thinning often needs to be practiced to improve berry size and marketability (Cirami et al., Citation1992). Also, other cultural practices, including the design and architecture of the vine, may need to be drastically different in order to have a sustainable production.
During the past 27 years, the University of Idaho Pomology and Viticulture Program has experimented with several new fruit crops and as a result a new alternative fruit industry, consisting of different cultivars of table grapes, is emerging in Idaho. The goal of this research was to evaluate cluster shortening and cluster removal with and without trunk girdling on yield and fruit quality attributes in ‘Alborz’ seedless grape under the prevailing conditions of the Intermountain West region of the United States.
Materials and methods
General description of the experimental vineyard
The field trail was conducted at the University of Idaho Parma Research and Extension Center, near Parma, Idaho. The experimental site was located at 43.8° N latitude, 116.9° W longitude, and 673 m elevation above sea level, with an annual precipitation of about 297 mm and a sandy loam soil of pH ~7.3. About 70 days before planting the grapevines, the ground was prepared and fumigated with Toluene 2. A drip irrigation system was installed, and vines were irrigated according to the ETc information provided from the Agrimet Weather Station at the University of Idaho Parma Research and Extension Center. Materials were gathered from our grape nurseries in the United States.
Dormant cuttings of ‘Alborz’ (a mutation of ‘Flame seedless’) were gathered from the University of Idaho vineyards, propagated as self-rooted plants, and planted at 1.8 m × 2.7 m in the spring of 2010. The vines were trained into a bilateral cordon canopy system. General cultural practices were similar to the guidelines established in California but modified to suit the local growth cycle and conditions (Fallahi et al., Citation2011). Vines were sprayed with gibberellic acid (GA) three times, each time at 50 ppm. The first spray was made at the beginning of fruit set (berries at about 4 mm) and the second and third GA sprays were applied at a weekly interval after the first spray.
This study was conducted during the period of 2012 through 2014 (3 years) when vines were young. Each cordon arm was trained to have 10 clusters on each arm (a total of 20 clusters/vine). In this study, we had five treatments as follows: (1) no shoot or cluster removal and no cluster shortening or control (NoClRemNoClShort); (2) no cluster removal but cluster shortening (NoClRembutClshort), (3) cluster removal but not cluster shortening (ClRembutNoClshort); (4) cluster removal and cluster shortening (ClRem&ClShort); and (5) cluster removal, cluster shortening, and vine girdling (ClRemClShort&Gird). In treatments with cluster removal, number of shoots was reduced to 10 per arm, each with one cluster (20 arms and clusters per vine). These shoots were trained upright in each arm. In the ClRemClShorGird treatment, 10 shoots, each with one cluster, were selected and the tip of clusters were removed by about one third, and all shoots other than these 10 selected ones were removed. In any treatments with cluster removal treatment (ClRem), only 10 clusters per arm, spaced evenly along a 60-cm arm, remained and the remaining clusters were removed entirely. In any treatment with NoClRem treatment, no cluster was removed on a 60-cm arm (all clusters remained on the arm). In any treatment with “short” or shortening, about one third from the tip of each cluster was shortened. Cluster cutting, girdling, and cluster removal were practiced when berry diameter was about 4–5 mm.
Table grape fruit quality attributes, including berry size, color, berry skin characteristics, and cluster weight at harvest were measured according to the procedures described by Fallahi et al. (Citation2011). Skin color was visually ranked on a scale of 1 = greenish or poor red, progressively to 5 = 100%, most red. Soluble solids concentration was measured using a temperature-compensated refractometer (Atago N1, Tokyo, Japan). Three berries from each of the 20 clusters were sampled to make a composite sample of 60 berries from each vine, and the average berry weigh was calculated. Berry diameter of each of these berries was measured using a digital caliper (Ironton, Northern Tool and Equipment, Burnsville, MN, USA).
Experimental designs and statistics
The experiment was arranged based on a completely randomized design in each of the 3 years. There were six blocks, each with a vine. The assumption of normal data distribution was checked by performing univariant analyses for all vines.
Analyses of variance were conducted using SAS (Citation2007), with PROC GLM and means separated using Fisher’s Protected Least Significant Difference at P ≤ 0.05.
Results and discussion
Vines that did not receive shoot or cluster removal or cluster shortening (NoClRemNoClCut) had higher yield but lower berry weight than those with other cluster managements (). Although these differences were not always significant, they became significant when values of each of the first and second harvests were pooled over all 3 years (). As anticipated, cluster length in the vines with NoClRemNoClCut and ClRembutNoClCut were always significantly longer than all other regimes (). Longer clusters in NoClRemNoClCut resulted in a greater number of berries (data not shown) and higher yield per vine despite their smaller berry size ( and ).
Table 1. The influence of cluster management regimes on yield and berry weight in ‘Alborz’ seedless grape.
Table 2. The influence of cluster management regimes on length and weight of cluster in ‘Alborz’ seedless grape.
Table 3. The influence of cluster management regimes on berry color and soluble solids concentration in ‘Alborz’ seedless grape.
Vines with ClRemShort&Gird regime tended to have larger berries and cluster weight than those with other treatments. However, girdling is a risky practice and may cause some of the following problems: (1) Since the movement of carbohydrates can be restricted during the time that vines are not hilled, roots will receive lower levels of sugar and the root growth will be limited. (2) Unskilled workers may injure the vine excessively while girdling, resulting in injuries that cannot be cured. (3) Girdling also adds to the cost of table grape production and will reduce profits. Fortunately, in our study, cluster removal and cluster shortening without girdling treatments produced berries with statistically the same berry weight as those girdled vines (). Thus, commercial growers can avoid practicing girdling without major cuts in the profit margin.
Vines receiving cluster removal and cluster shortening had slightly larger berries and had better appearance and berry color than those without cluster removal but with cluster shortening (). In general, vines with both cluster removal and cluster shortening had better appearance and better berry quality, leading to better marketability (data not shown). Therefore, considering all quality and yield attributes, vines that received cluster removal and cluster shortening appeared to have an optimum production (about 20 clusters/young vine) with good quality attributes; therefore, this cluster management regime is recommended for production of young (4- to 5-year-old) vines.
We concluded that if vines were completely mature and received ClRem&ClShort treatment, they could have 28 clusters per vine (14 clusters per arm) with superior quality.
Conclusions
Removal of clusters down to 10 clusters per arm (20 clusters/vive) and shortening of about 33% from the tip of the remaining clusters would lead to good berry size and packable cluster size in young ‘Alborz’ table grape. It is recommended to obtain larger berry size by cultural practice other than girdling, such as reduction of cluster numbers and tipping the clusters, as girdling may increase the chance of winter injury in the vines and shoots.
Funding
This work was funded by Snake River Table Grape Association.
Additional information
Funding
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