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  • Author or Editor: Youssef Rouphael x
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A greenhouse experiment was carried out to determine the effect of cationic proportions (K, Ca, Mg) in the nutrient solution on carotenoids and α-tocopherol content at green–orange, orange, red, and intense-red ripening stages using a high-pigment tomato (Lycopersicon esculentum Mill.) cultivar hp (`Lunarossa') and a standard cultivar (`Corfù') grown in a soilless culture. The highest lycopene concentration was observed in the `hp' cultivar at the red and intense-red ripening stages (3.0 mg/100 g fresh weight and 3.2 mg/100 g fresh weight respectively). In both cultivars, the concentration of β-carotene increased during the ripening stages, reaching the highest value (0.6 mg/100 g fresh weight) at the intense-red stage. The hp cultivar has guaranteed higher lycopene (average, 2.0 mg/100 g fresh weight vs. 1.7 mg/100 g fresh weight) and α-tocopherol contents (average, 1.2 mg/100 g fresh weight vs. 0.9 mg/100 g fresh weight) than those of the standard. In both cultivars, a high proportion of K in the nutrient solution increased antioxidant concentration β-carotene and especially lycopene) during the red and intense-red ripening stages, followed by Mg. The lowest values were recorded for the Ca treatment. Lastly, a positive correlation was recorded between fruit tissue K and lycopene content, whereas a negative correlation was observed between fruit tissue Ca and lycopene content.

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Three greenhouse experiments were carried out to compare the responses of Aloe arborescens and Aloe barbadensis with organic fertilization (standard or reduced fertilization level), arbuscular mycorrhiza [with AM (+AM) or without AM (–AM)], and salinity (1 or 80 mm NaCl) in terms of plant growth, leaf yield, mineral composition, and nutraceutical value. In all experiments, the yield of fresh leaves was significantly higher by 320%, 252%, and 72%, respectively, in A. barbadensis in comparison with A. arborescens. Doubling the fertilizer dose, plant growth parameters increased, but the bioactive compounds were negatively affected. The highest antioxidant activity was recorded with A. barbadensis using both fertilization regimes, whereas the highest values of anthraquinones aloin were observed in A. barbadensis using a reduced fertilization regime and when plants were inoculated with AM fungi. β-polysaccharide concentration was significantly higher in A. barbadensis in comparison with A. arborescens and was increased by 33% when plants were inoculated with AM fungi. In both Aloe species, increasing the salinity decreased the leaf fresh weight and total dry biomass but increased the aloin and β-polysaccharides content by 66% and 21%, respectively. The results suggest that cultural practices such as organic fertilization, inoculation with AM fungi, and irrigation with saline water can represent effective tools to achieve a more favorable phytochemical profile.

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Grafting represents an effective tool for controlling the race 1,2 of Fusarium oxysporum f. sp. melonis (FOM) and Didymella bryoniae in melon (Cucumis melo L.). Although not considered a soilborne pathogen, D. bryoniae survives on plant remains in the soil. The lack of effective resistant commercial hybrids and the gradual reduced use of soil fumigation with methyl bromide increase the risk of damages by both these pathogens. We determined the effectiveness of eight commercial rootstocks, ‘RS 841’, ‘P 360’, ‘ES 99-13’, ‘Elsi’ (Cucurbita maxima Duchesne × Cucurbita moschata Duchesne), and ‘Belimo’, ‘Energia’, ‘Griffin’, ‘ES liscio’ (Cucumis melo genotypes), for their resistance to FOM and D. bryoniae. During 2003 and 2004 growing seasons, the inodorus F1 hybrid Incas was grafted onto each of these commercial rootstocks and then evaluated, under greenhouse conditions, in terms of productivity and fruit quality. Cucurbita rootstocks (‘RS 841’, ‘P 360’, ‘ES 99-13’, ‘Elsi’) were highly resistant both to the race 1,2 of FOM (100% survival) and to D. bryoniae (almost absent crown lesions and low leaf disease index); this reaction clearly differed from that of both the C. melo rootstocks (‘Belimo’, ‘Energia’, ‘Griffin’, ‘ES liscio’) and the control Incas. In both years, the highest yield was recorded in the graft combination Incas/‘RS 841’ with 5.6 and 8.1 kg·m−2 during 2003 and 2004, respectively. The Cucurbita rootstock ‘RS 841’ produced yields higher than C. melo rootstocks (‘Belimo’, ‘Energia’, ‘Griffin’, ‘ES liscio’) and the control Incas. Fruit dry matter, titratable acidity, total soluble solid contents, fruit firmness, and Hunter color [L* (brightness), a* (redness), and b* (yellowness) parameters] of grafted melons were similar to those of the plants grown on their own roots.

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In a 2-year study, the morphophysiological and qualitative changes imposed to greenhouse lettuce (Lactuca sativa L.) by an increasing concentration of NaCl in the irrigation water were determined. Plants were grown under soil conditions and supplied with irrigation water having electrical conductivities (ECs) of 0.7 (control), 0.9, 1.8, 3.6, or 7.2 dS·m−1. Irrigation with saline water resulted in linear decrease in plant growth parameters (i.e., leaf number, total leaf area and head diameter), head fresh weight, and diameter as well as yield, especially at 1.8, 3.6, and 7.2 dS·m−1, confirming that lettuce is a salt-sensitive crop. The percentage of marketable yield reduction in comparison with nonsaline control treatment was 22.7%, 36.4%, 45.4%, and 63.6% at 0.9, 1.8, 3.6, and 7.2 dS·m−1, respectively. The reduction in marketable fresh yield has been partly compensated by a decrease in the nitrate content of salt-treated lettuce. The highest values of hydrophilic antioxidant activity were recorded in the nonsalinized treatment. The lowest values of lipophylic antioxidant activity (LAA) and total ascorbic acid were observed under severe stress conditions (7.2 dS·m−1). Net CO2 assimilation rate and leaf water potential (LWP) declined with increasing NaCl concentration in the irrigation water. Increasing salinity in the irrigation water induced a reduction in stomatal conductance (g s) as LWP dropped below −0.62 MPa.

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Accurate and nondestructive methods to determine individual leaf areas of plants are a useful tool in physiological and agronomic research. Determining the individual leaf area (LA) of small fruit like raspberry (Rubus idaeus L.), redcurrant (Ribes rubrum L.), blackberry (Rubus fruticosus L.), gooseberry (Ribes grossularia L.), and highbush blueberry (Vaccinium corymbosum L.) involves measurements of leaf parameters such as length (L) and width (W) or some combinations of these parameters. A 2-year investigation was carried out during 2006 (on seven raspberry, seven redcurrant, six blackberry, five gooseberry, and two highbush blueberry cultivars) and 2007 (on one cultivar per species) under open field conditions to test whether a model could be developed to estimate LA of small fruits across cultivars. Regression analysis of LA versus L and W revealed several models that could be used for estimating the area of individual small fruit leaves. A linear model having LW as the independent variable provided the most accurate estimate (highest R 2, smallest mean square error, and the smallest predicted residual error sum of squares) of LA in all small fruit berries. Validation of the model having LW of leaves measured in the 2007 experiment coming from other cultivars of small fruit berries showed that the correlation between calculated and measured small fruit berries LAs was very high. Therefore, these models can estimate accurately and in large quantities the LA of small fruit plants in many experimental comparisons without the use of any expensive instruments.

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