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Said Ennahli and Sorkel Kadir

Variability due to soil types, topography, and climate within a vineyard influences grapevine physiological parameters and fruit quality. Technical feasibility of using precision Geographic Information System (GIS) as a viticulture tool to improve vineyard management and increase wine quality will be investigated. The study was conducted in an experimental vineyard where rows consist of plots with 24 cultivars and selections randomly planted and managed similarly. Monitored vineyard parameters collected by Global Positioning System (GPS) location include soil characteristics, soil moisture, vine growth, crop load, and fruit characteristics. Geospatial maps are used to differentiate yield between the cultivars and selections as high, medium, or low. Production was determined from each variety/selection within the vineyard. Yield parameters were number of clusters, cluster weight, and weight of 50 berries; fruit composition (such as pH), titratable acidity, soluble solids concentration, and anthocyanins were measured. Maps for each factor will be derived via GIS tools and spatial analysis will be conducted to assess which spatial variability factor has more effect on grapevine physiology, yield, and fruit quality. This type of analysis can be used by grape growers to achieve specific wine characteristics in a large or small vineyard by controlling all sources of variability, leading to the ability to perform precision viticulture in the future, with low cost.

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Said Ennahli and Sorkel Kadir

Partial root-zone drying (PRD) irrigation management has been developed for grapevines as an efficient method to control excessive growth, improve fruit quality, and save water without compromising yield. PRD is based on knowledge of the mechanisms that control transpiration and requires slow dehydration of half of the plant root system, whereas the other half is irrigated. A study was conducted in the field to evaluate the effect of PRD on physiological characteristics, growth, yield, and fruit quality of three grape cultivars. The wetting and drying cycle of the PRD-vine root system is alternated on a 10–14 day schedule. Significant reduction in vigor was observed in treated plants compared with control plants. Root biomass was not affected, but fine roots significantly increased in PRD-treated plants, compared with that of the control. This contributed to the ability of PRD-treated plants to maintain leaf water potential similar to that of the control. Stomatal conductance of PRD plants was significantly reduced when compared with that of the control plants. Abscisic acid (ABA) concentration in leaves of PRD vines increased significantly when compared to the control vines. PRD treatment significantly increased yield and fruit quality when compared with the control treatment. PRD significantly increased water use efficiency (pruning weight per unit of water applied). This study shows that PRD stimulated ABA production in the drying roots, which caused reduction in stomatal conductance and transpiration rate, leading to a substantial reduction in vegetative growth without compromising yield and fruit quality.

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Sorkel Kadir, Edward Carey, and Said Ennahli

Plant growth, yield, and fruit quality of two strawberries (Fragaria ×ananassa Duch.)—`Chandler' and `Sweet Charlie'—grown under high tunnels (HTs) were compared with that of field plants during 2002–03 and 2003–04 growing seasons. Plug plants were planted in mid-October 2002 and mid-September 2003 on raised beds covered with black polyethylene mulch. Microclimate of the HTs protected strawberry crowns from winter damage and advanced fruit production 5 weeks earlier than that of plants grown under field conditions. From December to February, average minimum and maximum crown temperatures under the HTs were 5 and 12 °C warmer than those of the field crowns, respectively. The earliest HT fruit were harvested on 7 Apr. 2003 and 11 Mar. 2004. Yield and fruit quality under the HTs were superior to that of field-grown plants. HT plants, especially `Sweet Charlie', bloomed earlier than did field plants, but `Chandler' produced higher yield than `Sweet Charlie' late in the season. Larger fruit with higher soluble solids concentration (SSC) were produced inside the HTs than outside. HT `Sweet Charlie' fruit were sweeter than `Chandler' fruit, but `Chandler' produced larger fruit. Larger leaf area, greater number of leaves and shoot biomass, more branch-crowns, and fewer runners were developed under HTs than field conditions. Total leaf area, leaf production, total shoot biomass, and number of branch-crowns of HT `Chandler' were greater than HT `Sweet Charlie'. Results of this study indicate that strawberry plants under HTs were not only precocious, but also produced higher yields and superior quality to that of field plants. HT conditions suppressed runner growth, but enhanced branch-crown 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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Sorkel Kadir, Said Ennahli, and Ben Glass

Interactive effects of different temperature regimes and anti-transpiration organic materials, Surround WP (kaolinite clay) and Raynox (sun-protectant), on two strawberry (Fragaria ×ananassa) cvs. Chandler and Sweet Charlie were investigated under controlled environmental conditions. Newly planted strawberries treated with Surround and Raynox were subjected to 20/15, 30/25, and 40/35 °C (day/night) temperature regimes and 16 day/8 night photoperiod in growth chambers for 42 d. Photosynthesis (A) and photochemical efficiency (Fv/Fm) were measured at 7-d intervals during the experiment. Plants treated with Raynox displayed greater resistance to high temperature (40/35 °C) compared to those treated with Surround. Net photosynthesis of both cultivars decreased significantly with time at 40/35 °C. There was no significant difference in photosynthetic rate between the two cultivars. Nevertheless, there was difference in plant biomass between the cultivars. Raynox provided more protection against high temperature, specifically in reducing stomatal conductance and limiting transpiration, than Surround.