C. Leonardi

Analysis of Growth and Water Relations of Tomato Fruits in Relation to Air Vapor Pressure Deficit and Plant Fruit Load

The influence of air vapor pressure deficit (VPD) and plant fruit load on the expansion and water relations of young tomato fruits grown in a glasshouse were evaluated under summer Mediterranean conditions. The contributions of phloem, xylem and transpiration fluxes to the fruit volume increase were estimated at an hourly scale from the growth curves of intact, heat-girdled and detached fruits, measured using displacement transducers. High VPD conditions reduced the xylem influx and increased the fruit transpiration, but hardly affected the phloem influx. Net water accumulation and growth rate were reduced, and a xylem efflux even occurred during the warmest and driest hours of the day. Changes in xylem flux could be explained by variations in the gradient of water potential between stem and fruit, due to changes in stem water potential. Misting reduced air VPD and alleviated the reduction in fruit volume increase through an increase in xylem influx and a decrease in fruit transpiration. Under low fruit load, the competition for assimilates being likely reduced, the phloem flux to fruits increased, similarly to the xylem and transpiration fluxes, without any changes in the fruit water potential. However, different diurnal dynamics among treatments assume variable contributions of turgor and osmotic pressure in F3 and F6 fruits, and hypothetical short-term variations in the water potential gradient between stem and fruit, preventing xylem efflux in F3 fruits.

A simple model for nondestructive leaf area estimation in bedding plants

Measurement of leaf area is commonly used in many horticultural research experiments, but it is generally destructive, requiring leaves to be removed for measurement. Determining the individual leaf area (LA) of bedding plants like pot marigold (Calendula officinalis L.), dahlia (Dahlia pinnata), sweet William (Dianthus barbatus L.), geranium (Pelargonium × hortorum), petunia (Petunia × hybrida), and pansy (Viola wittrockiana) involves measurements of leaf parameters such as length (L) and width (W) or some combinations of these parameters. Two experiments were carried out during spring 2010 (on two pot marigold, four dahlia, three sweet William, four geranium, three petunia, and three pansy cultivars) and summer 2010 (on one cultivar per species) under greenhouse conditions to test whether a model could be developed to estimate LA of bedding plants across cultivars. Regression analysis of LA versus L and W revealed several models that could be used for estimating the area of individual bedding plants leaves. A linear model having LW as the independent variable provided the most accurate estimate (highest R2, smallest mean square error, and the smallest predicted residual error sum of squares) of LA in all bedding plants. Validation of the model having LW of leaves measured in the summer 2010 experiment coming from other cultivars of bedding plants showed that the correlation between calculated and measured bedding plants leaf areas was very high. Therefore, these allometric models could be considered simple and useful tools in many experimental comparisons without the use of any expensive instruments.

Effects of salt stress imposed during two growth phases on cauliflower production and quality

BACKGROUND Cultivation of cauliflower is diffused in Mediterranean areas where water salinity results in the need to identify alternative irrigation sources or management strategies. Using saline water during two growth phases (from transplanting to visible appearance of inflorescence or from appearance of inflorescence to head harvest), the present study aimed to identify the growth period that is more suitable for irrigation with low quality water in relation to cauliflower production and quality. RESULTS Salinity affected cauliflower growth mainly when imposed in the first growth phase. The growth reduction depended mainly on ion-specific effects, although slight nutrient imbalances as a result of Na+ and Cl- antagonisms were observed. The use of non-saline water in the first or second growth period reduced both the osmotic and toxic effects of salinity. When salinity was applied during inflorescence growth, yield was reduced because of a restriction of water accumulation in the head. CONCLUSION The results of the present study demonstrate the possibility of producing marketable cauliflower heads under conditions of salinity by timing the application of the best quality water during the first growth phase to improve fruit quality and during the second phase to reduce the negative effects of salinity on yield.

Effects of Nutrient and NaCl Salinity on Growth, Yield, Quality and Composition of Pepper Grown in Soilless Closed System

The effects of nutrient or sodium chloride (NaCl) salinity on pepper grown in closed soilless culture systems were studied. A control (2 dS m−1) and two saline nutrient solutions (4 dS m−1) differing in the salt sources (fertilizers or NaCl) were studied. Shoot biomass production as well as total and marketable yield were more affected by NaCl than nutrient salinity. Fruit dry matter and total soluble solids increased in both salinity treatments compared to the control. Total phenol content rose slightly (10%) with NaCl salinity, while the concentration of carotenoids was enhanced by 40% with NaCl compared to the control and nutrient salinity. The results showed that the response of pepper to salinity is both osmotic and ion specific, but a more negative effect was recorded under NaCl stress. Moreover, the highest content of antioxidant compounds in NaCl treated fruits may indicate that NaCl caused more stressful conditions than nutrient salinity.

The influence of rootstock on growth and ion concentrations in pepper (Capsicum annuum L.) under saline conditions

SUMMARY A study was conducted to evaluate the influence of rootstock on the growth and ion concentrations in pepper (Capsicum annuum L.) plants under salt stress. Pepper plants (‘Ibleor’) were grafted onto three different rootstocks (‘Atlante’, ‘Galaxy’, and ‘Robusto’). Non-grafted ‘Ibleor’ plants were also studied as controls. Treatments consisted of a non-saline nutrient solution or two iso-osmotic saline plus nutrient treatments (30 mM NaCl and 20.5 mM Na2SO4). Grafting did not enhance the growth of pepper plants under non-saline conditions, whereas reductions in growth due to salinity were attenuated in grafted plants compared to non-grafted plants. The different levels of tolerance of the three rootstocks to salinity did not appear to be related to the capacity of each genotype to maintain leaf turgor by osmotic adjustments, but did appear to be associated primarily with a reduced uptake of toxic ions and, therefore, to a lower concentration of these ions in the grafted plants. The nutritional status of plants exposed to either saline treatment was influenced only slightly by grafting.

Polyphenol composition and qualitative characteristics of fresh-cut lettuce in relation to cultivar, mulching, and storage

Summary The characteristics and nutritional quality of fresh-cut vegetable products during shelf-life depend on the raw material as well as on pre- and post-harvest factors. In this work, three of the commercially most widespread lettuce cultivars (‘Montego’, ‘Great Lakes 118’ and ‘Salad Bowl’), characterised by different qualitative traits, were cultivated under two different conditions, processed using standard conditions for fresh-cut lettuce, packaged in plastic trays and stored for 9 d at 5°C. Visual and texture analyses were performed, with determinations of polyphenol composition and of anti-oxidant activity. The results showed that the concentration of polyphenols was different in the three varieties, and was highest in ‘Salad Bowl’. The main polyphenols found were chlorogenic acid and kaempferol-3-O-glucoside in ‘Montego’, chlorogenic acid and quercetin-3-O-glucoside in ‘Great Lakes’, and kaempferol-3-O-glucoside, rutin and dicaffeoyltartaric acid in ‘Salad Bowl’.The practice of mulching during the growing period leads to an increase in yield; moreover, it also affects the total quantity of polyphenols, but not the qualitative pattern of polyphenols formed in each variety. During storage, a deterioration in sensory characteristics was observed, but this was not accompanied by any significant change in polyphenol content.

Nitrogen metabolism and ion content of sweet pepper under salt and heat stress.

The effects of salinity and high temperature stress conditions which often occur during greenhouse cultivation have been investigated in sweet pepper (Capsicum annuum L.). The responses were evaluated by measuring growth,nitrate content and reduction, protein and chlorophyll contents, proteolytic activity, as well as Na + , K + , Ca 2 + and Cl - contents. Plants exposed to salt stress strongly reduced growth and reproductive activity. In addition, salinity caused higher rates of membrane-bound NR activities and higher levels of total chlorophyll. Na + and Cl - contents increased. On the contrary, high temperature did not affect growth and reproductive activity. In response to heat, pepper showed a significant increase in the NADH-dependent NR activity and increased nitrate content suggesting a possible enhancement in nitrate uptake during heat stress. A slight increase in chlorophyll content and a strong reduction in Na + and Cl - content were observed under the same conditions.

Arsenic uptake and partitioning in grafted tomato plants

Arsenic is a toxic and cancerogenic metalloid that poses a threat to food crop consumption. Previous studies have shown that grafting vegetables onto certain rootstocks may restrict the uptake of some toxic metals, such as cadmium, lead, and so on, but these studies did not investigate the uptake of arsenic. The aim of this work was to determine the following: i) if grafting can influence and reduce arsenic translocation in the root and/or aerial organs; ii) how tomato plants irrigated with arsenic-enriched nutrient solution (100 μg·L-1) accumulate this metalloid; and iii) if arsenic poses a potential risk to fruit quality. We found that differences in plant growth and the qualitative traits of fruits were mainly related to the adopted rootstock rather than to the addition of arsenic. Grafting influenced metalloid accumulation in roots and its translocation from roots to shoots and fruits. Tomato plants accumulated arsenic in their roots, and only a small portion was translocated to shoots and fruits, making the risk for human consumption negligible. Therefore, the uptake of this toxic element and its translocation are influenced by the rootstock utilized.

Nutrient solution concentration on pepper grown in a soilless closed system: yield, fruit quality, water and nutrient efficiency

Abstract The aim of the experiment was to verify how the adoption of a reduced strength nutrient solution in a soilless closed system could influence the production and quality of pepper and improve the use efficiency of water and minerals. Two nutrient solutions characterized by the same ion ratio but macronutrient concentration equal to 100% or 60% were adopted. The total yield did not differ between the treatments; however the lower concentration of nutrients determined a significant reduction of incidence of unmarketable fruits (blossom-end rot) and thus a higher marketable production (+15%). Within the fruit quality characteristics the dry matter content and the titratable acidity were significantly higher adopting the full strength nutrient solution. Important differences were found when the agronomic water use efficiency was considered: the weight of marketable pepper produced per m3 of water input was about 32% higher using the reduced concentration treatment according to the lower volume of water released in the environment due to the lower renewal of recirculated nutrient solution. A similar pattern was observed for the use efficiency of the main nutrients. With reduced strength nutrient solution the amounts of nitrogen, phosphorus and potassium released per ton of marketable tomatoes were respectively 83%, 80% and 81% lower than the control. The use of a reduced strength nutrient solution in soilless closed system for pepper cultivation did not influence the total yield and improved the use efficiency of water and minerals. Moreover, the environmental impact of the system was drastically reduced.

Tomato and eggplant scions influence the effect of rootstock under Na2SO4 salinity

A short-term experiment was conducted to investigate whether the effect of rootstock on plant response to salinity depends on the solanaceous species used as scion. Tomato cv. ‘Ikram’ and eggplant cv. ‘Black Bell’ were grafted onto two tomato interspecific hybrids (‘Beaufort’ and ‘He-Man’). Plants were grown in an open soilless cultivation system and supplied with two nutrient solutions: non-saline control and a saline solution (adding 15 mM Na2SO4, 3.7 dS m−1). Plant dry biomass production and partitioning were influenced by salinity, but its effect was depending on the rootstock/scion combination. ‘Beaufort’ eliminated the deleterious effect of salinity when tomato was used as scion, but reduced (−29.6%) the shoot biomass of eggplant. ‘He-Man’ had a different effect on scion growth under saline conditions: shoot biomass was less reduced in eggplant (−20.6%) than in tomato (−26.8%). Under salt stress, ‘Beaufort’ reduced the accumulation of Na+ in tomato leaves more than in eggplant, whereas no differences were observed between tomato and eggplant grafted onto ‘He-Man’. Stem Na+ accumulation followed a different pattern. The increase of Na+ in the stems was similar for tomato and eggplant grafted onto ‘Beaufort’, whereas stems of tomato accumulated more Na+ compared to eggplant grafted onto ‘He-Man’. The opposite response of the tested rootstocks to salt stress when the scion was either tomato or eggplant seems to be partially related to the capacity of the rootstock and scion to exclude Na+ from the shoot. However, the results of nutrient accumulation within plant tissues imply that other mechanisms in addition to ion competition are involved in the salt resistance of grafted plants.