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  • Author or Editor: Pietro Santamaria x
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This research was conducted to determine the effect of potassium (K) and cultivar on important quality traits of tomato (Solanum lycopersicum L.), including reducing sugar, titratable acidity, and vitamin E content. Tomato plants were grown in a soilless system. Three K levels (low, middle, and high equal to 150, 300, and 450 mg·L−1 in the nutrient solution, respectively) and three cultivars (SVR, Kabiria, and Esperanza) were compared. Among cultivars, Kabiria, which is characterized by smaller fruits, showed 23% higher total soluble solids (TSS) than the average of the other cultivars. ‘Kabiria’ also showed a total tocopherol (vitamin E) content (18.5 mg·kg−1), markedly higher than SVR and Esperanza cultivars (12.2 and 10.3 mg·kg−1, respectively). Increased K levels in the nutrient solution resulted in increased contents of TSS, reducing sugar contents and titratable acidity in tomato fruits. Also, the vitamin E content of tomato fruits was significantly affected by differing K concentrations in the nutrient solution.

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Two greenhouse experiments were carried out to analyze the shoot sodium (Na+) partitioning, yield, and fruit quality of ‘Cuore di Bue’, a salt-sensitive heirloom tomato (Solanum lycopersicum L.), ungrafted or grafted onto interspecific tomato hybrid rootstocks (S. lycopersicum × S. habrochaites) ‘Maxifort’ and ‘Arnold’ in 2009, ‘Arnold’ and ‘Armstrong’ in 2010, grown at different salinity stress (SS) levels (0, 20, and 40 mm of NaCl in 2009; 0 and 20 mm of NaCl in 2010). In both experiments, an interaction was observed between grafting combinations and SS levels in terms of fruit yield, and fruit juice Na+ content. Under no SS conditions, plant grafted onto ‘Maxifort’ and ‘Armstrong’ provided the highest yield in 2009 and 2010 experiments, respectively. In the presence of 20 mm of NaCl, plants grafted onto ‘Arnold’ provided a marketable yield 23.5% (on average) higher than plants grafted onto ‘Maxifort’ or ungrafted in 2009 and 33% (on average) higher than plants grafted onto ‘Armstrong’ or ungrafted in 2010. The further increase of SS to 40 mm of NaCl considerably reduced the productivity of all grafting combinations. At 20 mm of NaCl, plants grafted onto ‘Arnold’ showed also a higher capacity to modulate shoot Na+ partitioning with respect to ungrafted plants by increasing Na+ accumulation in older leaves (52%) and reducing Na+ content in younger and most active leaves (24%), thus enabling the maintenance of higher K+/Na+, Ca2+/Na+, and Mg2+/Na+ ratios compared with ungrafted plants. Fruit total soluble solids content, titratable acidity, and dry matter were unaffected by grafting at any SS level, whereas under SS, the fruit juice Na+ content of grafted plants was consistently lower (from 19% up to 68%) than that of ungrafted plants. Under moderate SS conditions (20 mm of NaCl), the use of rootstock genotypes such as ‘Arnold’ having a particular ability to reduce Na+ accumulation in younger and most active leaves may increase tomato yield and enhance tomato nutritional value by reducing the fruit juice Na+ content.

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Sustainability of the soilless greenhouse system is under discussion in open cycle systems, where excess nutrient solution (NS) draining from the substrate is released into the environment. Closed growing systems (CGS) lead to the saving of water and fertilizers. The aim of this research was to compare two CGS: nutrient film technique (NFT) and trough-bench technique [Subirrigation (SUB)]. We report the results of yield and water use efficiency (WUE) of tomato (Lycopersicon esculentum Mill. cv. Kabiria) plants. NFT plants were grown with two electrical conductivity (EC) levels (2-4 and 6-8 dS·m-1) of NS (its highest EC was obtained by increasing all the ions therein). In the SUB system, two water tensions (-4 and –8 kPa) of susbtrate were compared; a NS with an electrical conductivity level of 2 dS·m-1 was used. The tensions were measured through tensiometers. Tomato plants were transplanted at the fourth to fifth true-leaf stage into pots containing 8 L of perlite for SUB. In both CGS, the plants were placed on steel gullies (slope of 2%). Six clusters per plant were harvested. Total and commercial yield were not influenced by the CGS (on average, 1959 and 1853 g/plant, respectively). The average weight of the fruit was lower in the SUB system's plants (40 vs. 43 g/fruit, respectively, for SUB and NFT). Salinity and water stresses resulted in a reduction of 26% of the yield and 16% of the average weight of fruits. The WUE was higher in SUB than NFT (30.7 vs. 26.0 g·L-1, respectively). Salinity stress reduced WUE (29.4 v.s 22.6 g·L-1 with 2–4 and 6–8 dS·m-1, respectively), whereas water stress did not.

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Nutrient solutions (NS) containing moderate to high concentrations of salts are frequently supplied to improve the taste of tomato fruits grown in soilless systems. The aim of this study was to determine whether salinity and water stress affect the tomato fruit quality similarly. The research was conducted in Mola di Bari, Italy, during Autumn 2004, and compared the nutrient film technique (NFT) with the trough-bench technique [Subirrigation (SUB)] in terms of tomato (Lycopersicon esculentum Mill. cv. Kabiria) fruit quality. In the NFT, the plants were grown with two electrical conductivity (EC) levels (2–4 and 6–8 dS·m-1) of NS. The highest EC was obtained by increasing all the ions in the NS. In the SUB system, two water tensions (-4 and -8 kPa) of substrate (perlite) were examinated. At harvest, in each cluster (six/plant), fruit dry matter (DM) and total soluble solids (TSS) were determinated. In the fourth and sixth cluster, vitamin C content and titratable acidity were determined. Total yield was not influenced by either soilless system, while the average weight of the fruit was lower in the SUB. The DM and TTS were influenced by soilless system (on average, 6.6 vs 7.3 g/100 g of fresh matter and 5.3 vs. 5.9 °Brix, with NFT and SUB, respectively). Both of the stresses resulted in the increase of DM and TSS, principally in SUB (water stress) in respect to NFT (salinity stress), while vitamin C and titratable acidity were not influenced by soilless system or water/salinity stress (25.2 mg/100 g fresh matter and 0.45 g/100 mL of citric acid juice, respectively). Results of NFT with the highest EC of NS exceeded 9 dS·m-1, without any stress symptoms in the plants, while EC in the SUB system remained unchanged (about 2.5 dS·m-1).

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Posidonia [Posidonia oceanica (L.) Delile] is a marine phanerogam endemic of the Mediterranean Sea that grows all along the coast forming extensive underwater meadows. Senescent posidonia leaves, together with fibers (residues of rhizomes and decomposed leaves), periodically accumulate along Mediterranean beaches, covering vast areas of coast. Removal and disposal of these large volumes of plant biomasses represent a high cost for local administrations. Therefore, in this experiment, beached residues of posidonia were composted with olive pruning and green wastes with the objective to assess the efficacy of posidonia-based compost (63% on a volume basis) as a peat replacement. The compost was then mixed with a peat-based commercial substrate at rates of 0% (C0, pure peat-based commercial substrate tested as control), 25% (C25), 50% (C50), 75% (C75), and 100% (C100, pure posidonia-based compost) v/v. Mixtures were used as growing media to produce lettuce seedlings for transplant. Two lettuce cultivars (8511RZ and Satine) were tested. Main physical and chemical properties of the five growing media, shoot and root fresh and dry weight, leaf area, root morphology, and elemental leaf tissue composition were studied. Growing media containing posidonia-based compost, C25 and C50 in particular, showed good physical properties. Increasing compost proportions in the mixtures resulted in enhanced: 1) availability of macro- and micronutrients in the growing media; and 2) overall growth parameters of lettuce seedlings, in particular for the cultivar Satine. In conclusion, posidonia-based compost shows a considerable potential as a peat substitute in horticultural substrates; posidonia residues are a low-cost renewable material. In growing media for lettuce seedlings production, posidonia-based compost could be used as a complement to peat at a rate of 25% or 50% to obtain optimal physical properties and to limit the negative effects of high B content, which are typical of posidonia residues.

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