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Youssef Rouphael and Giuseppe Colla

Zucchini plants (Cucurbita pepo L. cultivar Afrodite) were grown during a summer–fall season in closed-soilless systems using a mixture peat–pumice to evaluate the effects of irrigation system (drip irrigation and subirrigation) and nutrient solution concentration (half = 1 dS·m−1 and full = 2 dS·m−1) in terms of substrate electrical conductivity (ECs) using the dilution 1:1.5 media:water method, growth, yield, leaf mineral composition, fruit quality, and mineral solution composition. At the end of the cultural cycle, the highest ECs at the upper (0 to 7.5 cm) and lower (7.5 to 15.0 cm) layers were recorded with subirrigation using a full nutrient solution concentration. The highest plant growth, yield, and leaf macroelements concentration (nitrogen, phosphorus, and potassium) were recorded in both irrigation systems using a full-strength solution, followed by drip irrigation, and finally by subirrigation treatment using a half-strength nutrient solution. Fruit yield, fruit mineral composition (phosphorus, potassium, calcium, and magnesium), and leaf macroelements concentration (nitrogen, phosphorus, potassium, and magnesium) were substantially reduced when the concentrations of macronutrients in the feed solution were lowered to 50% of control. Using half-nutrient solution concentration, the marketable yield reduction was more pronounced with subirrigation (58%) than with drip irrigation (42%). The variation of the macronutrient and EC in the solution during the growing cycle was less pronounced in the subirrigation than with the drip irrigation system, which represents an important aspect for the simplification of the closed-loop management of the nutrient solution.

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Giuseppe Colla, Jeff Mitchell and Durga Poudell

A 2-year field study was conducted within the Sustainable Agriculture Farming Systems Project at the Univ. of California, Davis, to evaluate the effects of long-term conventional (CONV), low-input (LOW), and organic (ORG) production practices on processing tomato fruit mineral composition and quality. To establish relationships between soil chemical properties, soil water content, fruit mineral composition, and quality, this study characterized soil chemical properties and monitored soil water content through each tomato season. Soil total C, N, soluble P, exchangeable Ca, K,and Na were higher in the organic system than in the conventional system. Higher soil electrical conductivity was found in the CONV system compared to the other systems. Low input plots had soil characteristics intermediate to the other farming systems. Marketable and unmarketable yields were similar among the farming systems. Fruit N and Na were lower in the organic and low-input systems than in the conventional system. Fruit P and Ca contents were higher in the organic system than in the conventional system as a result of 11 years of manure applications. Soluble solids content, titrable acidity, color, and soluble solids yield were lower in 1998 in the organic system than in the conventional system, while no differences were found in 1999. Soil water content during the ripening stage was the major factor affecting the soluble solids content of the organic system. In the low input and conventional systems soluble solids content was most related to soil exchangeable Ca and EC, respectively.

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Daniela Borgognone, Mariateresa Cardarelli, Luigi Lucini and Giuseppe Colla

Supplemental calcium application has been reported to alleviate the detrimental effect of NaCl-induced salinity on crop growth. Iso-molar solutions of NaCl and NaCl plus CaCl2 were used to study the osmotic and ionic effects of salinity on leaf dry biomass production and nutraceutical quality of cardoon (Cynara cardunculus L. var. altilis DC) grown in a floating system. A basic nutrient solution (control; T1) was enriched with 15 mm of NaCl + 10 mm of CaCl2 (T2), 30 mm of NaCl (T3), 30 mm of NaCl + 20 mm of CaCl2 (T4), or 60 mm of NaCl (T5). NaCl at 60 mm induced a 52% reduction of total leaf dry biomass compared with the control (T1); the iso-molar solution enriched with 20 mm of CaCl2 (T4) increased the total leaf dry biomass production in comparison with treatment containing NaCl at 60 mm (T5). Moreover, at moderate salinity (T2 and T3), the partial replacement of NaCl with 10 mm of CaCl2 (T2) in treatment containing 30 mm of NaCl did not help to reduce the adverse effect of NaCl on total leaf dry biomass production. Results of leaf mineral analysis demonstrated that the partial replacement of NaCl with CaCl2 reduced the accumulation of sodium and the nutrient imbalance. Nutrient solutions enriched with CaCl2 did not increase the accumulation of the osmoprotectant proline in leaves. Nutraceutical value of cardoon leaves was generally improved by saline treatments compared with the control. The regression analysis between phenolic compounds and antioxidant activity showed that total phenols and chlorogenic acid were the major determinants of antioxidant activity in cardoon leaf biomass. In conclusion, the partial replacement of NaCl with CaCl2 improved the leaf dry biomass production of cardoon only at the highest salinity levels with a limited effect on nutraceutical quality of leaves.

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Giuseppe Colla, Carolina María Cardona Suárez, Mariateresa Cardarelli and Youssef Rouphael

Identification of rootstocks capable of improving the nitrogen use efficiency (NUE) of the scion could reduce N fertilization and nitrate leaching; however, screening different graft combinations under field conditions can be costly and time-consuming. This study evaluated a rapid and economical methodology for screening of melon rootstocks for NUE. Two experiments were designed. In the first, melon plants (Cucumis melo L. cv. Proteo) either ungrafted or grafted onto four commercial rootstocks: ‘Dinero’ and ‘Jador’ (Cucumis melo L.), ‘P360’, and ‘PS1313’ (Cucurbita maxima Duchesne × Cucurbita moschata Duchesne) grown in hydroponics were compared in terms of shoot dry biomass, leaf area, root-to-shoot ratio, SPAD index, shoot N uptake, and nitrate reductase (NR) activity at the early developmental stage in response to nitrate availability (0.5, 2.5, 5, 10, or 15 mm of NO3 ). The second experiment was aimed to confirm whether the use of a selected rootstock with high NUE (‘P360’) could improve crop performance and NUE of grafted melon plants under field conditions. In the first experiment, carried out under greenhouse conditions, melon plants grafted onto ‘Dinero’, ‘Jador’, and ‘P360’ rootstocks needed 5.7, 5.2, and 6.1 mm of NO3 , respectively, to reach half-maximum shoot dry weight, whereas plants grafted onto ‘PS1313’ rootstock and the control treatment (ungrafted plants) needed 9.1 and 13.1 mm of NO3 , respectively. Total leaf area, SPAD index, and shoot N uptake increased linearly and quadratically in response to an increase of the N concentration in the nutrient solution. At 2.5 mm of NO3 , melon plants grafted onto both C. melo and Cucurbita maxima × Cucurbita moschata rootstocks had the highest NR activity, whereas no significant difference was observed at 10 mm of NO3 . In the second experiment, carried out under open field conditions, increasing the N fertilization rates from 0 to 120 kg·ha−1 increased the total and marketable yields of melon plants, whereas the NUE decreased. When averaged over N levels, the marketable yield, NUE, and N uptake efficiency were higher by 9%, 11.8%, and 16.3%, respectively, in ‘Proteo’ grafted onto ‘P360’ than in ungrafted ‘Proteo’ plants.

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Mariateresa Cardarelli, Youssef Rouphael, Francesco Saccardo and Giuseppe Colla

A research project was conducted at the University of Tuscia, Viterbo (central Italy), to set up a vegetative propagation system for producing diseasefree artichoke transplants (Cynara cardunculus var. scolymus) of the Romanesco type (cultivar C3). The system included the following steps: 1) micropropagated plantlets were grown in a soilless culture year-round in greenhouse conditions, starting at the end of August; 2) stock plants were periodically treated with a chemical growth regulator [6-benzylamino purine (BA)] and then cut back at the collar level to promote offshoot production; 3) offshoots were periodically harvested and cold stored; and 4) cuttings were rooted at the end of spring under conditions of high humidity in multi-pack trays so as to be ready for summer transplanting. Results showed that the foliar application of BA to the stock plants increased the offshoot number quadratically to 200 mg·L-1. The rooting percentages of cuttings and root growth were enhanced by raising the cutting weight class (30-45 g) and by the application of naphthaleneacetic acid (NAA) to the cutting root zone at a rate of 2000 mg·L-1. The percent rotten cuttings increased as the 2 °C cold-storage time increased from 30 to 150 days. Similarly, the percentage of rooting and root growth decreased approximately from 60 to 150 days.

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Mariateresa Cardarelli, Youssef Rouphael, Francesco Saccardo and Giuseppe Colla

Research was conducted at the University of Tuscia (central Italy) to validate the propagation system for globe artichoke (Cynara cardunculus var. scolymus) described in a previous paper for a 1-year production cycle. The resulting globe artichoke plants were used in a 2-year field trial to investigate the field response of plantlets obtained with our propagation technique in comparison with plantlets produced by in vitro propagation and by offshoots harvested in commercial fields. The total number of artichoke plantlets obtained with our propagation system was 62.7 plantlets/m2 per year. In the first year, the globe artichoke production (bud number and fresh bud weight) was higher in plants obtained with our propagation system and by micropropagation than in those obtained from offshoots harvested in commercial fields. The production cost of plantlets obtained with our propagation technique was 52% lower than those of the micropropagated plantlets. This could lead to a significant reduction of production costs for artichoke growers, while preserving the advantages of in vitro propagation (disease-free plants and plant uniformity).

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Mariateresa Cardarelli, Youssef Rouphael, Delia Muntean and Giuseppe Colla

The fertilizer nitrogen (N) inputs to some potted plants such as ornamental cabbage (Brassica oleracea L. var. acephala D.C.) are frequently higher than the actual demand. Optimization of N fertilization rate and selecting N-efficient cultivars are important approaches to increase the nitrogen use efficiency (NUE) and to reduce environmental pollution from nitrate leaching. The aim of this study was to assess the effect of increasing levels of nitrate (0.5, 2.5, 5, 10, or 20 mm of NO3 ) in the nutrient solution on plant growth, quality, soil plant analysis development (SPAD) index, chlorophyll fluorescence, leaf pigments, mineral composition, and NUE in five ornamental cabbage cultivars (Coral Prince, Coral Queen, Glamour Red, Northern Lights Red, and White Peacock), grown in closed subirrigation system. ‘Glamour Red’ and ‘Northern Lights Red’ needed 3.3 and 2.9 mm of NO3 in the supplied nutrient solution, respectively, to produce 50% of predicted maximum shoot dry weight (SDW), whereas the vigorous cultivars Coral Prince, Coral Queen, and White Peacock needed 5.5, 4.7, and 4.3 mm of NO3 , respectively. Total leaf area (LA), SDW, SPAD index, N, Ca, and Mg concentrations increased linearly and quadratically in response to an increase of the nitrate concentration in the nutrient solution. Irrespective of cultivars, fertilizing above 10 mm NO3 produced high-quality plants (quality index of 5) and resulted in sufficiently high tissue concentrations of N, P, K, Ca, Mg, and Fe.

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Giuseppe Colla, Mariateresa Cardarelli, Paolo Bonini and Youssef Rouphael

The current research aimed 1) at evaluating the effects of three biostimulants (legume-derived protein hydrolysate, PH; plant and seaweed extract, PE and SWE) on yield performance and nutritional quality, mineral profiling, antioxidant activities, lycopene, total phenols and ascorbic acid of greenhouse tomato (Solanum lycopersicum L.) under soil culture and 2) to assess the economic profitability of biostimulant applications. Plants were sprayed four times during the growing cycle with a solution containing 1, 3, and 3 mL·L−1 of PE, SWE, and PH, respectively. Foliar applications of biostimulants improved the early and total marketable yield of fresh tomato. The increase of total yield by PE, SWE, and PH was 11.7%, 6.6% and 7.0%, respectively, in comparison with untreated plants. Legume-derived PH increased lycopene, total soluble solids, and K and Mg contents, thereby increasing the nutritional value of the fruits. The applications of SWE, and to a lesser degree PH, enhanced the Ca concentration in the fruit tissue. Our findings indicated that the three tested biostimulants, although they increased the total production cost, improved the nutrient status and yield performance of the crop to a level resulting in net economic benefits.

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Youssef Rouphael, Mariateresa Cardarelli, Luigi Lucini, Elvira Rea and Giuseppe Colla

A greenhouse experiment was conducted in Summer and Fall 2011 at the experimental farm of Tuscia University, central Italy, to study the effect of nutrient solution concentration (4, 20, 36, 52, or 68 mequiv·L−1) on biomass production, mineral composition, and concentrations of the major polyphenols in ‘Romolo’ artichoke and ‘Bianco Avorio’ cardoon grown in a floating system. Leaf dry biomass, leaf number, and macroelement concentrations (nitrogen, potassium, calcium, and magnesium) of artichoke and cardoon increased in response to an increase in the nutrient solution concentration, whereas an opposite trend was observed for the total polyphenols, phenolic acids (chlorogenic acid, cynarin, and caffeic acid), and the flavonoid luteolin. Artichoke and cardoon gave maximum biomass production and leaf number at 45 and 54 mequiv·L−1, respectively. Cardoon showed higher biomass and leaf number (average 1.13 kg·m−2 and 14.0 n./plant, respectively) than those observed in artichoke (average 1.07 kg·m−2 and 12.7 n./plant, respectively). The chlorogenic acid, cynarin, caffeic acid, and luteolin concentrations were higher by 204%, 462%, 580%, and 445% in cardoon leaf tissue than in that of artichoke. An improvement of leaf quality (total polyphenols, phenolic acids, and flavonoids) was obtained at the expense of leaf yield through the use of lower fertilizer concentrations in the nutrient solution.

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Youssef Rouphael, Mariateresa Cardarelli, Giuseppe Colla and Elvira Rea

Limited water supply in the Mediterranean region is a major problem in irrigated agriculture. Grafting may enhance drought resistance, plant water use efficiency, and plant growth. An experiment was conducted in two consecutive growing seasons to determine yield, plant growth, fruit quality, leaf gas exchange, water relations, macroelements content in fruits and leaves, and water use efficiency of mini-watermelon plants [Citrullus lanatus (Thunb.) Matsum. and Nakai cv. Ingrid], either ungrafted or grafted onto the commercial rootstock ‘PS 1313’ (Cucurbita maxima Duchesne × Cucurbita moschata Duchesne), under open field conditions. Irrigation treatments were 1.0, 0.75, and 0.5 evapotranspiration rates. In both years (2006 and 2007), marketable yield decreased linearly in response to an increase in water stress. When averaged over year and irrigation rate, the total and marketable yields were higher by 115% and 61% in grafted than in ungrafted plants, respectively. The fruit quality parameters of grafted mini-watermelons such as fruit dry matter and total soluble solids content were similar in comparison with those of ungrafted plants, whereas titratable acidity, K, and Mg concentrations improved significantly. In both grafting combinations, yield water use efficiency (WUEy) increased under water stress conditions with higher WUE values recorded in grafted than ungrafted plants. The concentration of N, K, and Mg in leaves was higher by 7.4%, 25.6%, and 38.8%, respectively, in grafted than in ungrafted plants. The net assimilation of CO2, stomatal conductance, relative water content, leaf, and osmotic potential decreased under water stress conditions. The sensitivity to water stress was similar between grafted and ungrafted plants, and the higher marketable yield from grafted plants was mainly the result of an improvement in nutritional status and higher CO2 assimilation and water uptake from the soil.