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Yi Zhang and Imed Dami

The purpose of this study was to develop a protocol to increase freezing tolerance of field-grown ‘Chambourcin’ grapevines (Vitis spp.) using exogenous abscisic acid (ABA). The specific objectives were to determine the optimum concentration and timing for ABA foliar application in ‘Chambourcin’ and to evaluate morphological and physiological changes that lead to increased freezing tolerance in response to foliar ABA application. ‘Chambourcin’ grapevines were treated with a foliar ABA application of concentrations of 0, 100, 200, 300, 400, 500, 600, 700, and 800 mg·L−1 at 50% fruit set stage to evaluate ABA phytotoxicity under field conditions and identify the optimum concentration. In a subsequent experiment, ‘Chambourcin’ grapevines were treated with 400 and 600 mg·L−1 of ABA at different stages of development corresponding to 50% fruit set, 21 days after 50% fruit set, 50% veraison, 20, 30, 40, and 55 days postveraison. ABA concentrations of 700 and 800 mg·L−1 were phytotoxic and caused significant damage to leaves and flowers. Optimum concentrations of ABA did not affect yield components or basic fruit chemical composition, yet it promoted anthocyanin accumulation at harvest. Furthermore, ABA advanced bud dormancy, decreased bud water content, and eventually increased freezing tolerance under simulated freezing tests. The increased freezing tolerance of ABA-treated vines was confirmed by bud injury assessment after a natural freezing event in Jan. 2011. It was also determined that ABA was most effective when applied with an optimum concentration of 400 mg·L−1 20 to 30 days postveraison. It is concluded that exogenous ABA enhanced dormancy and increased freezing tolerance; thus, it has the potential to protect grape cultivars from freezing injury.

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Imed Dami and Harrison Hughes

Micropropagated grapes (Vitis sp. `Valiant') were subjected to water stress while rooting with the addition of 2% (w/v) PEG 8000. PEG-treated plantlets exhibited reduced growth, as compared to control (in vitro, no PEG), but developed greater leaf epicuticular wax. PEG-treated plantlets had three times the wax level of control. Although treated plantlets showed changes in leaf anatomy, no effect on stomatal frequency or stomatal index was evident. Differences in epidermal cell configuration were also observed among leaves from different treatments. PEG-treated plantlets resembled those grown in the greenhouse, morphologically and anatomically, and exhibited a higher survival rate than control upon transfer to the greenhouse.

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Imed Dami and Harrison Hughes

Grape cv. Valiant was micropropagated in an MS medium with and without 2% (W/V) of polyethylene glycol (PEG, MW 8000). Leaf anatomy of control (in vitro, no PEG), treated (in vitro, PEG), field grown and greenhouse grown plants were compared under light microscopy. Cell size, palisade layer formation, relative intercellular air space and apparent chloroplast number varied between the leaves of control and PEG treated (high osmoticum) plantlets. These leaf characteristics in the high osmoticum medium appeared more similar to the leaves of the greenhouse and field grown plants. Leaves from control plantlets contained cells of larger size, lacked normal palisade layer formation, greater intercellular pore spaces and fewer chloroplasts. Leaves of PEG treated plantlets had smaller cells, a more defined palisade layer, reduced intercellular pore spaces and greater number of chloroplasts. Leaves of greenhouse and field grown plants had small cells, a well-defined palisade layer, least intercellular pore space and greatest number of chloroplasts. These results demonstrate that a high osmoticum medium may be used to induce more normal leaf development.

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Imed Dami, Said Ennahli and David Scurlock

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.

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Thomas M. Todaro and Imed E. Dami

‘Cabernet franc’ grapevines (Vitis vinifera) sustained severe winter injuries of all aboveground parts following two consecutive freezing events in 2014 and 2015 in Ohio. To ensure grapevine recovery, adjustment of pruning and training practices must be accomplished. However, optimum training of new shoots for trunk replacement was not known and research-based information on this topic was lacking. Therefore, the purpose of this study was to evaluate different training and pruning methods for trunk renewal and recovery of ‘Cabernet franc’ and their impacts on growth, yield, cropload, and fruit composition following severe winter injuries. In 2016, grapevines were manipulated using a combination of training [Fan, vertical shoot positioning (VSP), or both], pruning (cane- or spur-pruned), and trunks (two, four, or more trunks per vine). The Fan system took less time to train than VSP during the growing season; however, the latter took less time to train and prune during the following dormant season. Training and pruning methods with increased buds per vine resulted in increased shoots, leaf area, pruning weight, clusters, and yield per vine but decreased juice total soluble solids (TSS). The exceptions were vines with combined training systems of Fan and VSP, in which leaf areas and pruning weights were reduced despite increased bud count per vine after pruning. In conclusion, each system has advantages and disadvantages; however, the Fan training system with cane pruning and multiple trunks produced the most optimum trunk size, yield, cropload, and fruit composition. Therefore, following trunk freeze injury, we recommend retaining all shoots using the Fan training during the growing season. During the subsequent dormant season, growers should select medium-sized canes for trunk replacement and train four trunks and four canes for the VSP system.

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Richard Allen Hamman Jr. and Imed Eddine Dami

Field studies were conducted to determine the effect of three drip irrigation regimes on grapevine growth, juice and wine quality, soil moisture, cold hardiness of bud and cane tissues and soluble sugar content of cortical cane tissues of Vitis vinifera, Linnaeus `Cabernet Sauvignon'. This study was developed to help provide some irrigation management strategies that would improve fruit quality and reduce excessive vigor. Irrigation treatments of 192, 96, and 48 L (51, 25, and 13 gal) per vine per week were initiated at bud break until veraison (initiation of berry color) and then reduced by 25% through harvest. Significant differences of fruit weight per vine, crop load, soil moisture, average berry and cluster weight, shoot length and pruning weight per meter of canopy row were observed among treatments. Juice and wine compositions and wine color were also significantly different; however, cold hardiness and soluble sugar contents did not differ between treatments.

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Imed Dami, Cecil Stushnoff and Richard Hamman

The response of grapevines to methanol was investigated at the Orchard Mesa Research Center in Grand Junction, CO. Optimum sublethal methanol dose levels, based on visual assessments, were 90% for leaves and 100% for trunks for 10 cultivars. Total soluble sugars (TSS) of the berries, monitored every week until harvest, showed significant differences with Muscat Blanc during veraison. Berries from the methanol-treated vines had higher TSS (16.4 °Brix) than controls (15 °Brix). However, no significant differences were observed later in the season when approaching fruit maturity. At harvest, data on yields as estimated by cluster weight, berry weight and berry size showed no differences between the two treatments. Methanol did not enhance cold hardiness of bud tissues. measured by differential thermal analysis. It was concluded that, although methanol has been reported to improve several physiological features of C3 crops, our study suggested that it has little or no practical effect on grapes. More data on the determination of sugars in berries by HPLC will be discussed.

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Yi Zhang, Tracey Mechlin and Imed Dami

The purpose of this study was to investigate the influence of foliar application of abscisic acid (ABA) on grapevine dormancy, specifically to: 1) determine the optimum foliar application concentration of ABA and 2) evaluate the morphological and physiological changes of greenhouse-grown grapevines in response to exogenous ABA application. Vitis vinifera ‘Cabernet Franc’ and Vitis spp. ‘Chambourcin’ with different leaf ages (40, 50, 80, 100, 110, and 120 days) were subjected to foliar ABA application at different concentrations (0, 100, 200, 400, 600, 800, 1600, and 3200 mg·L−1) and to a cold-acclimated regime. Concentrations of 800 mg·L−1 or higher were phytotoxic and the optimum concentrations were between 400 and 600 mg·L−1. Optimum concentrations of ABA inhibited shoot growth and advanced growth cessation, periderm formation, and leaf senescence, which led to advanced dormancy in both cultivars. In this study, it was concluded that exogenous ABA induced endodormancy because single cuttings (not paradormant) under favorable growing conditions (not ecodormant) were used. Furthermore, grapevine response to ABA was influenced by leaf age and cold treatment. ABA was effective in inhibiting shoot growth and increasing periderm formation in the young vines with 40- to 50-day old leaves and the old grapevines with 80- to 120-day old leaves. However, ABA was effective in inducing early shoot cessation, leaf senescence and abscission, and dormancy in old vines with 100- to 120-day old leaves only. The advanced morphological and physiological changes induced by exogenous ABA mimicked those triggered by environmental cues during the cold acclimation process. It was suggested that advancing the cold acclimation process using foliar ABA application may be beneficial for long-season grape cultivars grown in regions with short growing seasons and early fall frost events.

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S. Kaan Kurtural, Imed E. Dami and Bradley H. Taylor

Response of yield components and fruit composition of `Chambourcin' (Vitis vinifera × V. rupestris) grapevines to three pruning levels of 15, 20, and 25 nodes retained for each pound of dormant prunings; and three cluster thinning levels of 1, 2, and 2+ clusters per shoot in 2002 and 1, 1.2, and 1.5 clusters per shoot in 2003 were measured at two vineyards in the lower midwestern United States. In both years of the study, there was very little interaction of pruning and cluster thinning. The proportion of non-count shoots increased within the canopy in response to increased pruning severity. Pruning weight means were lower in 2002 across all treatments compared to 2003. Pruning weights decreased with the increase in the number of clusters retained per vine. Pruning influenced yield only in 2003 when the proportion of count shoots decreased below 62% of the total, hence the relationship between number of shoots per vine and yield (R2 = 0.3452; P < 0.0003). In both years of the study, the increase in severity of cluster thinning resulted in yield reduction but an increase in the total soluble solids in juice. Yield compensation was achieved by an increase in cluster weight of 38%, and 25% in response to a reduction of 37%, and 23% in cluster numbers; which translated into a yield reduction of only 10% and 3%, at Vineyards 1 and 2, respectively. Balanced pruning to 15 to 20 nodes per 1 lb of prunings and cluster thinning to 1 to 1.2 clusters/shoot optimized yield (9.7 kg/vine, 13.4 t·ha-1) and fruit composition, and maintained vine size (≥0.3 kg·m-1 of row). These results provide valuable information for growers of `Chambourcin' grapevines in the lower midwestern U.S., as well as in other climates with long growing seasons.

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Imed Dami, Dave Ferree, Anton Prajitna and Dave Scurlock

`Chambourcin' (Vitis sp.) is a French-American hybrid cultivar that has the propensity to overcrop, and its performance under cool climate and short growing season is not known. This study was conducted for five years (2000 to 2004) to evaluate the effect of three levels of cluster thinning (10, 20, and 30 clusters per vine) on yield and fruit composition of `Chambourcin' grown in northeastern Ohio. Cluster thinning reduced yield per vine and crop load, but increased pruning, cluster and berry weights. Cluster thinning also improved juice composition by increasing soluble solids and pH but not acidity. It was concluded that under the climatic conditions of this study, thinning to 10 clusters per vine (or 8 clusters per meter of row) produced the lowest yield but the highest vine size with the most optimum fruit composition. Therefore, vines from the 10-cluster treatment were considered the most balanced in the 5-year study. Additionally, due to the repeated coincidence of harvest with the first fall frost, it was suggested that the site in continental Northeast Ohio is risky for commercial production and longer and warmer seasons are thus preferred.