This article is protected by copyright. All rights reserved Effect of Colored Shade Nets on Plant Leaf Parameters and Tomato Fruit Quality Zoran S. Ilić 1*, Lidija Milenković 1, Ljubomir Šunić1, Elazar Fallik 2 1Faculty of Agriculture Priština-Lešak, 38219 Lešak, Serbia 2ARO- Тhe Volcani Center, Postharvest Science of Fresh Produce, Israel *Corresponding author:
[email protected] Abstract BACKGROUND: The photoselective netting concept using commercial cultivation practices was studied in a tomato (Solanum lycopersicum ‘Vedetta’) summer cultivation in south Serbia (under high solar radiation 910 W·m-2, with a PPFD of 1661 μmol·m-2·s-1), under four different colored shade-nets (pearl, red, blue and black) with 40% relative shading. The aim of the study was to determine how different environmental control technologies (color shade nets as screen house or plastic-house integrated with color shade nets) could influence plant parameters, production and quality traits in tomato fruits cultivated in south Serbia (Balkan region). RESULTS: The leaf area index (LAI) ranged from 4.6 to 5.8 in open field and plastic tunnels plants (control) with maximum LAI values of 7.9 - 8.2 in net houses with red color nets. Shade-grown leaves generally have larger total chlorophyll and carotenoids content than control leaves. Pericarp thickness was significantly higher in pearl (7.215.82µm), red (7099.00µm) and blue nets (6802.29 µm) compared to other treatments and to control (6202.48 µm). The highest concentration of lycopene was detected in tomatoes grown in plastic houses integrated with red color nets (64.9 μg g-1 FW). The plastic house and open field (control) tomato production had a taste index mean value of 1.09-1.10. This is significantly higher than the values determined for the treatments with different color shade nets. CONCLUSSION: These results show that red and pearl photo-selective nets create optimal growing conditions for the growth of the plant and produces fruits with thicker pericarp, the highest lycopene content, satisfactory level of taste index and can be further implemented within protected cultivation practices. Key words : Solanum lycopersicum; LAI, chlorophyll-carotenoids; pericarp thickness; lycopene; taste index; This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. Please cite this article as doi: 10.1002/jsfa.7000 This article is protected by copyright. All rights reserved INTRODUCTION In traditional vegetable-producing regions, tomato cultivation in a protected environment has expanded to prevent seasonality in the availability of the fruit. Low-cost protected cultivation, such as plastic tunnels and net house, has the potential to reduce biotic and abiotic stresses, which affects productivity and quality (Rajasekar et al., 2013). Netting is frequently used to protect tomato crops from excessive solar radiation (Kong et al., 2013), to improve the thermal climate sheltering from wind and hail (Shahak, 2008; Stamps 2009; Rajapakse and Shahak 2007) and for exclusion of bird and insect-transmitted virus diseases (Shahak, 2014). In addition, photo-selective shade nets increase the relative proportion of scattered light, and also absorb various spectral bands, thereby modifying light environment (Shahak et al., 2004a; 2004b). Scattered light penetrates more deeply and efficiently into dense canopies and is therefore regarded as an important part of the ColorNet technology (Shahak et al, 2008). It is either applied by itself over net-house constructions, or combined with greenhouse technologies (Shahak et al., 2004a). Movable shade, applied only during sunny periods, is less deleterious than constant shade. The climate in south Balkan regions is characterized by hot summers, high solar radiation, dry weather and limited water resources. These stressful conditions require environmental control devices to improve the production and quality of tomato fruits (Leyva et al., 2014). The use of shading nets has become very popular in Serbia in the last two years due to the very high temperatures (35-40°C) in the summer season (Ilić et al., 2012). High temperatures during the growing season have been reported to be detrimental to growth, reproductive development and yield of tomato (Saeed et al., 2007). Radiation is the most important one, as it supplies the energy for photosynthesis, the basic production process in plants. Only radiation that is intercepted by the crop can contribute to photosynthesis. The leaf area index (LAI) in tomato is influenced by stem density, number of leaves on a stem, development stage, seasonality and individual leaf size (Heuvelink, 2005). Shading induced an LAI increase of about 40% compared to open field (Kittas et al., 2009). Reducing the LAI from 5.2 to 2.6, by removing old leaves, did not affect yield (Valdes et al., 2010). Differences in LAI between control (3.9 m2·m-2) and shade-grown plants (4.7) increased at successive harvests (Sandri et al., 2003). As the degree of shading was increased, leaves developed greater area per leaf, but less dry weight per unit area and per leaf. Chlorophyll content and photosynthetic capacity increased as the degree of shading was increased. In the available literature there are many studies that illustrate the beneficial effects of plant shading upon the yield and quality of tomato (Ilić and Milenković, 2012; Tinyane et al., 2013). Thus, shading reduced the appearance of tomato cracking and eliminated sun scalds on tomato fruits and accordingly, increased the marketable tomato production by about 35% compared to non-shading conditions (Ilić et al., 2012). It is well known that shading decreases the sugar content, ascorbic acid and pigments (carotenoids) of tomato fruit. This article is protected by copyright. All rights reserved The maturity index (ratio of total soluble solid to titrable acidity) is a good indicator of tomato ripeness (Gonzalez-Cebrino, 2011). Pearl and red photo-selective nets improved the overall fruit quality; fruit mass, fruit firmness and bioactive components of tomato. The effects of coloured photo- selective nets on quality parameters, bioactive compounds and the sensory parameters in tomatoes during post-harvest storage have been investigated by Tinyane et al. (2013). Tomato produced under pearl nets retained good fruit quality and acceptable taste after post-harvest storage (Selahle et al., 2014). Colored net house tomato production system must be fine-tuned to the local climatic conditions before the technology can be adopted by growers; this study is the first step in that direction. The aim of the study was to determine how different environmental control technologies (color shade nets as screen house or plastic-house integrated with color shade nets) could influence plant growth parameters, production and quality traits in tomato fruits cultivated in south Serbia (Balkan region). EXPERIMENTAL Plant material and cultivation Tomatoes (Solanum lycopersicon ‘Vedetta’) were tested in greenhouse production (plastic tunnels - 2.2 m high, covered by polyethylene film 0.15 mm thick) and open field condition during 2009-2011. The experiments were performed in an experimental garden located in the village of Moravac near Aleksinac, (Longitude: 21o42' E, Latitude: 43o30' N, altitude 159 m) in the central area of south Serbia. The shade nets were applied at the start of warm weather in early June. The color nets were mounted on a structure about 2.2 m height over the plants (net house) or integrated with plastic-house technologies (plastic tunnels covered by color nets). The houses were shaded for the rest of the summer and tomatoes were harvested until late August. Randomised block design was adopted with four treatments (red, blue, white, black and control). One way ANOVA was carried out using SAS programme and the means were compared using the Tukey’s multiple range test. The plants were grown following the technique that is usually implemented by the local producers. Substrate for the seedling production consisted of 30% soil, 50% manure and 20% peat and a small part of marble. Tomato seeds were sown on third week of February in seed trays containing a peat and perlite mixture. The seedlings were transplanted on April 30, at the third true leaf stage, to soil with a plant density of 2.64 plants/m2. Soil solarization against nematodes was applied before transplanting. It was an early-medium production. As the plants grew, all lateral shoots were manually removed, except for the lateral branches below the first inflorescence, which serve as second stem plants. The shading nets were subsequently installed above the crop on June 10 (40 days after transplanting) and the measurements were carried out until September 5. All plants were irrigated using drip irrigation. Plants were topped after the sixth truss, and bumblebees were used for pollination during the organic tomato production in the greenhouse. The tomato leaves used in the study were taken at DAT (day This article is protected by copyright. All rights reserved after transplanting) 90 at the most intensive harvest period (end of July). Tomato samples (20 fruits) at pink stage of ripening, as determined by visual inspection, were collected from the third to sixth floral branches for quality analyses. Net characteristics In order to test the effect of shading nets (color and shading intensity), four different shading nets were used: the photoselective nets including ‘colored-ColorNets’ (red, blue and black) as well as ‘neutral-ColorNets’ (pearl) with shading intensity of 40% relative shading, photosynthetically active radiation (PAR) were compared to the open field microclimate and production. The color shade nets were obtained from Polysack Plastics Industries (Nir-Yitzhak, Israel) under the trade mark ChromatiNet. These nets are unique in that they both spectrally-modify, as well as scatter the transmitted light. The photoselective net products are based on the incorporation of various chromatic additives, light dispersive and reflective elements into the netting materials during manufacturing. The shading nets were mounted on a structure about 2.2 m in height over the plants (net house) or combined with plastic tunnels technologies. Light interception by nets The effect of nets on the interception of light was measured annually as a percentage of total PAR above canopy, using a Ceptometer mod. Sun scan (SS1-UM-1.05, Delta-T Devices Ltd, Cambridge, UK) with a 64 sensor photodiode linearly sorted in a 100 cm length sword. Readings are in units of PAR quantum flux (μmol·m-2·s-1). All measurements were done on clear days at noontime, every second day. The Solarimeter-SL 100 (KIMO Instruments, UK) is an easy-to-use portable autonomous solarimeter that measures solar irradiation range from 1 W·m-2 to 1300 W·m-2. All spectral data were expressed as radiation intensity flux distribution in W m-2·nm-1. Weather measurement Monthly meteorological data from May to September 2009, 2010 and 2011 from the meteorological stations in Aleksinac were used (Figure 1). Chlorophyll and carotenoids analysis Chlorophyll a, b and carotenoids were estimated in fresh leaf samples. One-half g of fresh leaves were ground in acetone (90% v/v), filtered and made up to a final volume of 50 mL. Pigment concentrations were calculated (absorbance of extract at 663, 648 and 470 nm) using the formula of Lichtenthaler (1987). Chlorophyll a (mg·g-1 FW) = [(11.75 · A663- 2.35 · A645) · 50] / 500. Chlorophyll b (mg·g-1 FW) = [(18.61 · A645- 3.96 · A663) · 50] / 500. This article is protected by copyright. All rights reserved Carotenoids (mg·g-1 FW) = [(1000 · A470) - (2.27 · Chl a) - (8.14 · Chl b)/227 · 50] / 500. Direct methods for leaf area determination First, measure the length and width of paper and calculate the surface area (P), and then determine its mass (G) on the analytical balance. Then remove the leaves from the plant, put them on paper and pencil outline the edges of their contours. The outlined area on the paper is cut with scissors and determine its mass (G1). Since the values of P, G and G1 are known, then one can calculate the unknown leaf area (P1) using the formula: P1/P = G1/G, such that P1 = G1·P/G Fruit quality measures Tomato samples (20 fruits) were collected each year from June until August and were taken from the third to sixth floral branches. Each fruit was cut in to pieces and homogenized in a conventional blender (Braun, Safeway, UK) in order to obtain the fruit juice. Thereafter, the fruit juice was filtered using a Whatman No. 4 filter paper and the filtrate was used to determine the TSS and TA. Total soluble solids (TSS) were determined for each fruit sample in two replications using an Atago DR-A1 digital refractometer (Atago Co., Tokyo, Japan) at 20 °C and expressed as %. The titratable acidity (TA) was measured with 5 mL aliquots of juice that were titrated at pH 8.1 (Hanna GLP pH meter HI 111) with 0.1N NaOH (required to neutralize the acids of tomatoes in the presence of phenolphthalein) and the results were expressed as grams of citric acid per 100g of fresh tomato weight. The TSS to TA ratio (ripening index) was also calculated. Pigment extraction and analysis Ground tomato fruit (8 g) was thoroughly mixed with 40 mL of ethanol. The slurry was stirred until the tomato paste material was no longer sticky (about 3 min). Ethanol was removed by vacuum filtration. The retained tomato residue was mixed with 60 mL of a mixture of acetone and petroleum ether (1:1). The extract was collected by vacuum filtration, and the filter residue was rewashed with the solvent mixture (20 mL) in order to improve the yield. The filtrate was transferred to a small separatory funnel and mixed with 50 mL of saturated NaCl solution. The organic layer was rewashed twice, repeatedly, first with 50 mL of 10% potassium carbonate and then with 50 mL of water. Finally, approximately 1 g of anhydrous magnesium sulphate was added to dry the organic layer. After 10 to 15 minutes the solution was vacuum filtered to remove the drying agent (Cvetkovic and Markovic, 2008). The extracts (1 mL) with different concentrations were evaporated to dryness with rotary vacuum evaporators at room temperature and the residues were dissolved in mobile phase (acetonitrile: methanol: ethyl acetate, 6:2:2 v/v) to a concentration of 1 mg/cm3. Extracts were filtered through a 0.45 μm Millipore filter before the HPLC analysis. This article is protected by copyright. All rights reserved β-carotene and lycopene content of tomato fruit were measured by HPLC (Agilent 1100 Series system, Agilent) A C18 reverse phase column (4.6×250 mm, 5 μm; Zorbax, Agilent Co., New York, USA) was used for analysis and a mobile phase consisting of a mixture of acetonitrile: methanol: ethyl acetate, at a flow rate of 1 mL·min-1. The injection volume was 20 μL using the diode array detector (Agilent 1200 Series) at 470 nm wavelength. Standards of β-carotene and lycopene were dissolved in mobile phase (eluent: acetonitrile: methanol: ethyl acetate, 6:2:2 v/v) just before HPLC analysis. From these standards, a series of solutions of appropriate concentration for the calibration curve were made. The external standard method was used for the qualitative and quantitative determination of β-carotene and lycopene. A calibration curve representing the dependence of the peak area (of standard compound) in chromatograms on standard concentrations were made. Based on the obtained linear regression equation, the concentrations of the tested components in the extracts were determined. Taste index and index of maturity were calculated using the equation proposed by Nielsen (2003) starting from the Brix degree and acidity values, which were determined in a previous paper (Hernandez et al., 2008). Brix degree Brix degree Taste index = –––––––––– + Acidity Index of maturity = ––––––––––– 20 × Acidity Acidity Light microscopy Slides for light microscopy were made according to standard procedure. Samples were fixed in FAA for 24h, postfixed in 70% ethanol and dehydrated in a graded ethanol series. After tissue impregnation in Histowax (56-58 °C) samples were embedded. After cooling the blocks on a cold plate and solidifying paraffin, histological sections of about 5-7 μm were cut using a microtome (Leica SM 2000 R). Before staining, the paraffin is removed from the sections by xylene, followed by rehydration in graded series of ethanol, whereupon the tissue is stained by safranine and alcian blue. Statistical analysis All data were subjected to one-way statistical analysis at P = 0.05 using JMP Statistical Analysis Software Programme (SAS Institute Inc., Cary, NC, USA) and the mean values for all data are presented. RESULTS AND DISCUSSION Light interception by nets: The photosynthetic photon flux density (PPFD) of a day in July (13-14h) had a value of 1661 µmol·m-2·s-¹. By shading with shade nets, the PPFD was lowered to 962 µmol·m- 2·s-¹ in the red shade net, and to 771 µmol·m-2·s-¹ in the black shade net (Table 1). The sun rays in the tunnels are intercepted not only by nets but also by a foil which is 150µm thick. PPFD is highest in This article is protected by copyright. All rights reserved the tunnel with a red net of the shade index 40% PAR – 832.3 µmol·m -2 ·s-¹. In July around 1 pm, the sun radiation in the tunnel without nets is 761 W·m-², which is 16.4% less in comparison to the open field radiation (910 W·m-²). The sun radiation in July and August is high. It can reach 1700 µmol·m-2·s-¹ and it is most frequently followed by temperatures above 35°C. During a sunny day in July (with solar radiation at 910 W·m-2) the reduction did not exceed 1oC in plastic tunnels with shade. With every 100 W·m-2 solar radiations increase the temperature by 1oC. The net radiation is strongly correlated to the incoming solar radiation, in analogy to what is known to occur over open ground. Under high solar radiation conditions (in South Serbia in July and August) PPFD values exceed 1600 μmol·m-2·s-1, resulting in unshaded plants being exposed to high heat stress throughout the growing season (Table 1). The PPFD values varied between 1661 μmol·m-2·s-1 on sunny days and 700 to 920 μmol·m-2·s-1 on cloudy days. Similarly, Jaimes and Rada (2011) state that the PPFD at full insolation (1519 µmol·m- 2·s-¹) is lowered to 931 µmol·m-2·s-¹ when shaded to 40% PAR and to below 550 µmol ·m-2·s-¹ when shaded to 60% PAR. Microclimate conditions: Shade nets are often deployed over crops to reduce heat stress (Elad et al., 2007; Shahak et al., 2004a). Our studies show that in July and August, at high insolation and reduced air circulation (13-15h), the temperature in shade nets is 1°C lower (pearl and red) and up to 3°C lower (black), in comparison to the open field (data not shown). Shading technology on a number of locations in Israel confirmed a general decrease of maximum daily temperature (T max) by 1-5ºC, followed by an increase in maximum daily relative air humidity by approximately 3-10%. Shahak et al. (2004b) reported that the maximum daily temperature under shade nets (30% PAR) was up to 3 ºC lower than control, similar to what Iglesias and Alegre (2006) have stated, and that larger differences are recorded during bright and sunny days. Leaf area index (LAI): In this study we have found that red and pearl shade nets significantly increase the total leaf area, compared to the LAI values obtained from blue or black shade nets. Generally, tomatoes under plastic tunnels integrated with color shade nets have a lower LAI in comparison to the LAI obtained under net house (only color nets). Among the color nets, black shade nets produce crop with the lowest LAI value (Table 2). Leaf area indices ranged from 4.6 in open field crop (control) to maximum LAI values of 8.2 in net houses with red color nets (40% shade). The differences in LAI between control and shaded crops increased at successive harvests. Crop grown under black color nets had LAI values similar to control crop (Table 2). Lower light intensities increased the stem elongation, leaf blade area and leaf area index (Tinyane, 2013). Plants grown in the shade tend to have a larger leaf area because cell expand more under low light intensities in order to receive light for photosynthesis (Boardman, 1977). Higher LAI values are generally indicative of excessive vegetative growth which may delay the onset of fruit production (Heuvelink et al., 2005). Plants acclimate to shade, in part, by increasing the specific leaf area. This article is protected by copyright. All rights reserved Chlorophyll content: Shaded leaves generally have larger total chlorophyll (chlorophyll a and chlorophyll b) content than control leaves (from plastic house or open field). Plants from black shade nets have the highest chlorophyll content in comparison with other color shade nets (Table 3). An increase in biomass (vegetative and reproductive) coincides with increases in leaf area and chlorophyll content. Shade-grown leaves harvest lower levels of light, and thus contain more chlorophyll than leaves exposed to direct sun. Although shade-grown leaves are not directly exposed to sunlight, they produce additional chlorophyll to capture diffuse radiation to produce the carbohydrates needed for a plant to grow. Even if sun-exposed leaves contain less chlorophyll than shade-grown leaves do, they have a greater light saturation point and therefore can handle full exposure to the sun. Shade-grown leaves were of a softer texture and had a darker green coloration (Woltz, 1968). Thus, the shade-grown leaves had a conformation somewhat the opposite to that of leaves grown in high light intensity. Similar results were found by Bergquist et al. (2007) who showed that the concentrations of total carotenoids and total chlorophylls in baby spinach leaves were significantly higher under the nettings, especially under the spectrum-altering and low transmittance nettings. Since the nets are composed of holes, in addition to the translucent photo-selective plastic threads, shade nets actually create mixtures of natural, unmodified light, which is passing through the holes, together with the diffused, spectrally modified light and altered proportions of red/far-red waveband (R/FR) ratio (Shahak, 2008). The actual functions of colour shade net depend on chromatic additives to the plastic and the knitting design (Shahak, 2014). The increase in chlorophyll 'a/b' ratio might be associated with the protection of the photosynthetic system under stress conditions, due to a lesser radiation absorption at shorter wave length (Camejo and Torres, 2001). Carotenoids content ranged from 0.416 mg·g-1 in open field plants (control) to maximum carotenoids values in plants grown in net houses with black nets (0.508 mg·g-1 ) or in blue nets (0.500 mg·g-1) (Table 3). A similar trend was observed in plastic tunnels integrated with color shade nets where the lowest carotenoid content (0.380 mg·g-1) was recorded. The highest content of carotenoids in plastic tunnels was observed in plots integrated with blue (0.494 mg·g-1) or pearl nets (0.487 mg·g- 1). Tomato leaves grown under black and blue nets had significantly more total chlorophyll content than leaves from open field (control) or grown under pearl net. Similarly, tomato plants grown under black, pearl and blue nets had significantly more chlorophyll than leaves grown in a plastic tunnel (control) or under integrated plastic house with red net. Tomato leaves in open field (control) and under pearl net had significantly less carotenoids than leaves grown under black or blue nets. Tomato plants grown in plastic tunnels (control) and under integrated plastic tunnels with red net had significantly less carotenoid level than leaves grown under black, pearl and blue net. The chlorophyll a+b /carotenoids ratio increased in shade-grown leaves in comparison with control plants (open field or plastic tunnel). In terms of microclimate, it is likely to This article is protected by copyright. All rights reserved depend on air temperature, humidity, and day length, as these all influence aspects of plant physiology related to fruit development and composition (Gent, 2007). Fruit physical characteristics: The tomato fruit consists of pericarp and seeds. The elongated central placenta, with attached seeds, is made of parenchyma tissue and represents primary tissue, which later fills the locular cavities (Rancic et al., 2010). Tomatoes grown under pearl nets had the largest part of the fruit as pericarp, in relation to the total fruit mass. Results from this study indicate that the number of seeds and the fruit mass are significantly higher for tomatoes grown in red net house compared to other treatments and control. Tomatoes from pearl nets with 40% shade had the largest part of the fruit as pericarp (80.9%), with locular gel tissues (16.5%) and seeds (2.6%) contributing to the remainder of total fruit mass. It was statistically confirmed that there are differences in the percentages of mesocarp and gelatinous mass with treatment. The number of seeds (n=208) and the mass (5.4g) was consistently and significantly higher in fruits gown in a red net house compared to control (Table 4 and 5). The number of seeds per fruit in the autumn crop correlated with fresh fruit weight and volume. However another study observed no such correlation was observed in a summer crop (Thanopoulos et al., 2013). In summer, fruits have a lower number of seeds per fruit than in the autumn, because pollination and fertilization are restricted by the high temperatures and low relative humidity within the greenhouse at that time, whereas the higher humidity of the autumn favours fertilization. Rylski et al. (1994) reported that temperature and irradiation conditions at the early stages of flower development are important factors which determine yield and tomato fruit quality. Low temperature prevents fertilization and therefore, decreases fruit set but low irradiation cause puffiness and blotchy ripening. The pericarp consists of the exocarp, mesocarp and endocarp. The mesocarp is made from large thin wall cells and vascular tissue. Results indicate that the pericarp thickness is significantly higher in pearl and red color net houses compared to other treatments and control. The pericarp thickness (exocarp-126.37µm, mesocarp-7055.47µm and endocarp-33.98µm) is significantly higher in pearl (7.215.82µm) and red (7099.00µm) color nets compared to other treatments and control, open field tomato (6202.48 µm), (Table 4). Results indicate that high temperature tolerance of color shade applied plants is primarily linked to improved growth and fruit quality parameters. Although some reports show improvement in plant growth by color shade nets (Ilić and Milenković, 2012; Gent, 2007), no report is available on the enhancement of the tomato fruit composition in shade-grown plants. In this study, we found that color shade nets improved the fruit structural parameters. Therefore, the mechanical properties of tomato exocarp, mesocarp and locular gel tissues were determined in this paper, and the obtained data can be used to create optimal growing conditions to achieve fruits with thicker pericarp, firmness and better tolerated transport and storage. Lycopene and β-carotene contents of fruits: Most of the quality traits show a continuous variation, strongly influenced by environmental conditions. Lycopene is the most abundant carotenoid in the ripened tomato, accounting for approximately 80-90% of the total pigments (García-Valvedere et al., This article is protected by copyright. All rights reserved 2013). Tomatoes exposed to direct sunlight in the field often develop a poor colour, mainly because fruit exposed to high temperatures has low lycopene content. In fresh tomatoes the rate of lycopene synthesis is completely inhibited at 32-35oC, but not that of β-carotene. No significant differences in lycopene contents were observed in tomatoes grown in plastic houses (48.9 μg·g-1FW) compared to control, open field conditions (48.1 μg·g-1FW). The highest concentration of lycopene was detected in tomatoes grown in plastic houses integrated with red colour nets (64.9 μg·g-1FW), while tomatoes grown in fields covered with pearl nets had the lowest levels of lycopene (46.7 μg·g-1FW) (Table 6). Similar results were found by López et al. (2007) who showed that the lycopene content of tomatoes grown under red and pearl frame nets were 51 and 37 μg·g-1, respectively. The lycopene content was significantly higher in tomatoes grown under the black nets whereas the tomatoes grown under pearl nets had lower lycopene content. The observed variation was due to air temperature and light quality with lycopene content in tomatoes affected by higher temperatures. Lycopene biosynthesis depends on temperature and tends to take place at different day temperatures (at 12 to 32oC) with an optimal temperature around 22-26oC. According to Helyes et al. (2006) fruit surface temperature was a more accurate predictor of fruit lycopene content than air temperature. According to Brandt et al. (2006) when the temperature of the fruits exceeds 30oC, the formation of lycopene is inhibited. However, excessive sunlight was reported to inhibit the synthesis of lycopene (Brandt et al., 2006; Rosello et al., 2011). Total soluble solids and titratable acidity: Light intensity and temperature impact greatly on the sugar accumulation in tomatoes. Therefore, exposing fruit to higher temperatures, especially during fruit cell division and ripening, resulted in an increase in the total soluble solids (TSS). The TSS content in tomatoes is mostly composed of reducing sugars. The TSS content observed in fruits analyzed in this work ranged between 4.55-5.43 ºBrix. We found that a TSS content of 5.43 and 5.10 ºBrix for tomatoes grown in the field and in a plastic house, respectively. No significant differences were observed in the TSS values of fruits grown under control conditions (plastic house) and fruits grown in integrated plastic houses with different shade nets (Table 7). Organic acids in tomatoes influence the fruit taste (Migliori et al., 2012). Citric acid and malic acid are important fruit acids in tomato. For a tomato crop cultivated in summer, Wada et al. (2006) reported that fruit quality was characterized by a lower sugar content and that titratable acidity (TA) increased with high air temperatures. We found that field-produced fruits were more acidic (greater TA - 0.37%) than fruits produced in a protected environment (0.34%). Thus, the lower acidity of the fruits grown in a protected environment may be a result of the lower photosynthetic activity of the plant (shading in protected environment) in this environment, and consequently a lower carbohydrate accumulation in the fruits. TA also decreases with increased temperature (Cowan et al., 2014; Gauiter et al., 2008; Dumas et al., 2003). However, the effect of shading on the acidity was not clear in this experiment. This article is protected by copyright. All rights reserved Fruits produced in the field had higher TSS:TA ratio acidity than those produced in the protected conditions. The TSS/TA ratio (index of maturity) was reported as a useful indicator of tomato taste. According to Kader (1986) a TSS/TA of 12.5 indicates a good taste for table tomatoes. We found significantly greater index of maturity in control fruits, from open field (14.68) in comparison with fruits from colour shade nets. Significantly lower index of maturity were obtained in fruits covered by black shade nets integrated with plastic tunnels (12.95) and with black nets in screenhouse (12.65), as shown in Table 8. The index of maturity in our study (in all treatments) were higher than those reported by Hernández-Suárez et al. (2008) and therefore it can be deduced that the maturity levels of the analyzed tomatoes were adequate for consumption (Nielsen, 2003). This ratio can also be affected by climate, cultivar and horticultural practices (Nielsen, 2003). Another parameter related with the index of maturity is the taste index, which is usually a better predictor of an acid’s flavour impact than Brix degree or acidity alone. The plastic house and open field (control) tomato production had a taste index mean value of 1.09-1.10. This is significantly higher than the values determined for the treatments with different color shade nets (Table 8). No significant differences in the mean taste index were found between tomatoes from plastic houses integrated with color shade, and color shade nets (screenhouse) cultivated tomatoes. If the value of the taste index is lower than 0.7, the tomato is considered as having little taste (Navez et al., 1999). When using these data, the mean values of the taste index in tomatoes evaluated were higher than 0.9, which indicates that the tomato cultivars analyzed were tasty. CONCLUSIONS Our results show that shade application of color nets to tomato plants was effective in substantially improving vegetative growth parameters (leaf area index and leaf pigments) and fruit quality (mass, pericarp thickness, lycopene content, taste index) under excessive solar radiation during the summer period. The photo-selective, light-dispersive shade nets emerge as interesting tools that can be further implemented within protected cultivation practices. ACKNOWLEDGEMENTS: This study was (part of the TR-31027 project) financially supported by the Ministry of Science and Technological Development, Republic of Serbia. REFERENCES 1. Bergquist SAM, Gertsson UE, Nordmark LYG and Olsson ME, Ascorbic acid, carotenoids, and visual quality of baby spinach as affected by shade netting and postharvest storage. J Agric Food Chem 55: 8444-8451 (2007). This article is protected by copyright. All rights reserved 2. Boardman NK, Comparative photosynthesis of sun and shade plants. Ann Rev Plant Physiol 28: 355-377 (1977). 3. Brandt S, Pék Z, Barna E, Lugasi A and Helyes L, Lycopene content and colour of ripening tomatoes as affected by environmental conditions. J Sci Food Agric 86: 568-572 (2006). 4. Camejo D and Torres W, High temperature effect on tomato (Lycopersicon esculentum) pigment and protein content and cellular viability. Cultivos Tropic 22(3): 13-17 (2001). 5. Cowan JS, CA Miles, PK Andrews and Inglis DA, Biodegradable mulch performed comparably to polyethylene in high tunnel tomato (Solanum lycopersicum L.) production. J Sci Food Agric 94:1854-1864 (2014). 6. Gautier Y, Diakou-Verdin V, B´enard C, Reich M, Buret M, Bourgaud F, Poessel L, Caris-Veyrat C and Generd M, How does tomato quality (sugar, acid, and nutritional quality) vary with ripening stage, temperature, and irradiance? J Agric Food Chem 56:1241-1250 (2008). 7. Dumas Y, Dadomo M, Di Lucca GD and Grolier P, Effects of environmental factors and agricultural techniques on antioxidant content of tomatoes. J Sci Food Agric 83:369-382 (2003). 8. Cvetkovic D and Markovic D, UV-induced changes in antioxidant capacities of selected carotenoids toward lecithin in aqueous solution. Rad Phys Chem 77: 34-41 (2008). 9. Gent MPN, Effect of degree and duration of shade on quality of greenhouse tomato. Hort Sci 42: 514-520 (2007). 10. García-Valverde V, Navarro-Gonzáles I, García-Alonso J and Periago JM, Antioxidant bioactive compounds in selected industrial processing and fresh consumption tomato cultivars. Food Biopr Technol 6: 391-402 (2013). 11. Gonzalez-Cebrino F, Lozano M, Ayuso MC, Bernalte MJ, Vidal-Aragon MC and Gonzalez- Gomez D, Characterization of traditional tomato varieties grown in organic conditions. Span J Agric Res 9: 444-452 (2011). 12. Elad Y, Messika Y, Brand M, Rav-David D and Sztejnberg A, Effect of colored shade nets on pepper powdery mildew (Leveillula taurica). Phytoparasitica. 35: 285-299 (2007). 13. Heuvelink E, Bakker M J, Elings A. Kaarsemaker R and Marcelis LFM. Effect of leaf area on tomato yield. Acta Hort 691: 43-50 (2005). 14. Hernández-Suárez M, Rodriguez E R and Romero C D, Analysis of organic acid content in cultivars of tomato harvested in Tenerife. Eur Food Res Technol 226: 423-435 (2008). 15. Helyes L, Lugasi A, Pék Z and Brandt S, Analysis of antioxidant compounds and hydroxymethyl furfural in processing tomato cultivars. Hort Technol 16: 615-619 (2006). 16. Iglesias I and Alegre S, The effect of anti-hail nets on fruit protection, radiation, temperature, quality and profitability of ‘Mondial Gala’ apples. J App Hort 8: 91-100 (2006). 17. Ilić ZS, Milenković L, Stanojević L, Cvetković D and Fallik E, Effects of the modification of light intensity by color shade nets on yield and quality of tomato fruits. Sci Hort 139: 90-95 (2012). This article is protected by copyright. All rights reserved 18. Ilić ZS and Milenković L, The influence of photo-selective shade nets on quality of tomatoes grown under plastic tunnels and field conditions, International Conference on BioScience: Biotechnology and Biodiversity, Step in the Future. Book of the proceedings Novi Sad, Serbia, pp.25-34 (2012). 19. Jaimez RE and Rada F, Gas exchange in sweet pepper (Capsicum chinense Jacq.) under different light conditions. J Agric Sci 3: 134-142 (2011). 20. Kader A A, Effects of postharvest handling procedures on tomato quality. Acta Hort 190: 209-221 (1986). 21. Kittas C, Rigakis N, Katsoulas N and Bartzanas T, Influence of shading screens on microclimate, growth and productivity of tomato. Acta Hort 807: 97-102 (2009). 22. Kong Y, Avraham L, Perzelan Y, Alkalai-Tuvia S, Ratner K, Shahak Y and Fallik E, Pearl netting affects postharvest fruit quality in ‘Vergasa’ sweet pepper via light environment manipulation. Sci Hort 150: 290-298 (2013). 23. Lichtenthaler HK, Chlorophylls and carotenoids: pigments of photosynthetic membranes. Methods Enzymol 148: 350-382 (1987). 24. Leyva R, Constan-Aguilar C, Blasco B, Sanchez-Rodrıguez E, Romero L, Sorianoa T and Ruızb JM, Effects of climatic control on tomato yield and nutritional quality in Mediterranean screenhouse. J Sci Food Agric 94: 63-70 (2014). 25. Lopez D, Carazo N, Rodrigo MC and Garcia J, Coloured shade nets effects on tomato crops quality. Acta Hort 747: 121-124 (2007). 26. Migliori C, Di Cesare L F, Lo Scalzo L, Campanelli G and Ferrari V, Effects of organic farming and genotype on alimentary and nutraceutical parameters in tomato fruits. J Sci Food Agr 92: 2833-2839 (2012). 27. Navez B, Letard M, Graselly D and Jost M, Les crite´res de qualite´ de la tomate. Infos- Ctifl 155: 41-47 (1999). 28. Nielsen S, Food analysis (3rd ed.). New York: Kluwer Academic, USA (2003). 29. Rajapakse NC and Shahak Y, Light quality manipulation by horticulture industry. Light and Plant Development. In: Whitelam, G., Halliday, K. (ed.), Blackwell Publishing, UK (2007). 30. Rajasekar M, Arumugam T and Kumar SR, Influence of weather and growing environment on vegetable growth and yield. J Hort For 5(10): 160-167 (2013). 31. Rancic D, Pekic-Quarrie S, Radosevic R, Terzic M, Pecinar I, Stikic R and Jansen IS, The application of various anatomical techniques for studying the hydraulic network in tomato fruit pedicels. Protoplasma 246: 25-31 (2010). 32. Rylski I, Aloni B, Karni L and Zaidman Z, Flowering, fruit set, fruit development and fruit quality under different environmental conditions in tomato and pepper crops. Acta Hort 366: 45- 56 (1994). This article is protected by copyright. All rights reserved 33. Rosello S, Adalid A M, Cebolla-Cornejo J and Nuez F, Evaluation of the genotype, environment and their interaction on carotenoid and ascorbic acid accumulation in tomato germplasm. J Sci Food Agric 91: 1014-1021 (2011). 34. Saeed AK, Hayat A, Khan A and Iqbal S, Heat tolerance studies in tomato (Lycopersicon esculentum Mill.). Int J Agr Biol 9: 649-652 (2007). 35. Sandri M A, Andriolo J L, Witter M and Dal Ross T, Effect of shading on tomato plants grow under greenhouse. Hort Brasileira 21: 642-645 (2003). 36. Selahle M K, Sivakumar D and Soundy P, Effect of photo-selective nettings on post-harvest quality and bioactive compounds in selected tomato cultivars. J Sci Food Agric 94(11): 2187- 2195 (2014). 37. Shahak Y, Photoselective netting: an overview of the concept, r&d and practical implementation in agriculture. Acta Hort 1015: 155-162 (2014). 38. Shahak Y, Photo-selective netting for improved performance of horticultural crops. A review of ornamental and vegetable studies carried out in Israel. Acta Hort 770: 161-168 (2008). 39. Shahak Y, Gal E, Offir Y and Ben-Yakir D, Photoselective shade netting integrated with greenhouse technologies for improved performance of vegetable and ornamental crops. Acta Hort 797: 75-80 (2008). 40. Shahak Y, Gussakovsky EE, Cohen Y, Lurie S, Stern R, Kfir S, Naor A, Atzmon I, Doron I and Greenblat-Avron Y, ColorNets: a new approach for light manipulation in fruit trees. Acta Hort 636: 609-616 (2004a). 41. Shahak Y, Gussakovsky EE, Gal E and Ganelevin R, ColorNets: crop protection and light-quality manipulation in one technology. Acta Hort 659: 143-161 (2004b). 42. Stamps RH, Use of colored shade netting in horticulture. HortSci 44: 239-241 (2009). 43. Thanopoulos CH, Akoumianakis KA and Passam HC, The effect of season on the growth and maturation of bell peppers. Int J Plant Prod 7(2): 279-294 (2013). 44. Tinyane PP, Sivakumar D and Soundy P, Influence of photo-selective netting on fruit quality parameters and bioactive compounds in selected tomato cultivars. Sci Hort 161: 340-349 (2013). 45. Tinyane PP, Influence of photo-selectine netting on plant morphology, fruit quality and bioactive compounds in tomato cultivars. Faculty of Science, Tshwane University of Technology, Pretoria, South Africa, Master thesis pp. 160 (2013). 46. Valdes VM, Woodward GC and Adams SR, The effects of long-day lighting and removal of young leaves on tomato yield. J Hort Sci Biotech 85: 119-124 (2010). 47. Wada T, Ikeda H, Matsushita K, Kambara A, Hirai H and Abe K, Effects of shading in summer on yield and quality of tomatoes grown on a single-truss system. J Jap Soc Hort Sci 75: 51-58 (2006). This article is protected by copyright. All rights reserved 48. Woltz SS, Influence of light intensity and photosynthate export from leaves on physiological leaf roll of tomatoes. Florida Agricultural Experiment Stations. Journal Series No 3157. pp. 208-211 (1968). This article is protected by copyright. All rights reserved Table 1: Reduction in solar radiation, and incident photo synthetically active radiation (PAR), over tomato canopy measured at noon on a sunny day (20th July) under shade nets of different colors* Color of nets Reduction in solar radiation (%) PAR (μmol·m 2·s 1) PT + color nets Only color nets PT + color nets Only color nets Red 22.9 32.5 832.3 962.0 Black 52.4 55.9 703.1 771.8 Pearl 25.1 33.9 813.9 993.6 Blue 32.9 43.9 756.6 889.7 Control 100◘ 100◙ 1199.5◘ 1661.3◙ *Data are reproduced from conference paper (Ilić ZS and Milenković L, 2012). PT - Plastic tunnel Control: ◘-plastic tunnel (solar radiation -761W·m-2); ◙-open field (exposure to full sunlight-910 W·m-2) This article is protected by copyright. All rights reserved Table 2: Leaf area index (LAI) in tomato crop as affected by light intensity using color shade nets Color of nets Red Black Pearl Blue Control Plastic tunnel + color nets 7.9a 6.4ba 7.1ab 7.1ab 5.8b ◘ Only color nets 8.2a 5.1b 7.7a 7.2ab 4.6b ◙ Control: ◘-plastic tunnel; ◙-open field Distinct letters in the row indicate significant differences according to Tukey’s test (P ≤ 0.05). This article is protected by copyright. All rights reserved Table 3: Photosynthetic pigments (mg·g-1) in the leaves of tomato plants in response to light intensity using color shade nets Color of nets Chl a Chl b Car Chl a+b/ Car Chl a Chl b Car Chl a+b/ Car Plastic tunnels + color nets Only color nets Red 1.634c 0.688b 0.380c 6.11 1.409b 0.633b 0.442b 4.62 Black 1.982a 0.832a 0.475a 5.92 1.742a 0.728a 0.508a 4.86 Pearl 1.800b 0.724b 0.487a 5.18 1.261c 0.501bc 0.384b 4.58 Blue 2.046a 0.804a 0.494a 5.78 1.484b 0.634b 0.500a 4.23 Control 1.510d◘ 0.577c 0.436b 4.90 1.046c◙ 0.398c 0.416b 3.47 Control: ◘-plastic tunnel; Control: ◙-open field Distinct letters in the row indicate significant differences according to Tukey’s test (P ≤ 0.05) This article is protected by copyright. All rights reserved Table 4: Tomato fruit structural characteristics as affected by light intensity using plastic tunnel and color shade nets Color of nets Fruit mass(g) Seed mass (g) Seed number Exocarp (μm) Mesocarp (μm) Endocarp (μm) Pericarp (μm) Red 156.1a 3.7a 168.3a 151.33 a 7029.69 a 45.55 a 7226.57 a Black 128.5b 3.1b 111.0b 117.35 ab 6379.37 b 31.34 b 6528.06 b Pearl 161.0a 3.5a 158.3a 102.34 b 7105.97 a 43.33 a 7251.64 a Blue 132.9b 3.1ba 118.6b 109.77 ab 6966.92 a 44.90 a 7099.49 a Plastic tunnel ◘ 149.8a 3.6a 165.6a 108.85 ab 6176.18 b 42.01 a 6327.04 b ◘-plastic tunnel represent control Distinct letters in the row indicate significant differences according to Tukey’s test (P ≤ 0.05) This article is protected by copyright. All rights reserved Table 5: Tomato fruit structural characteristics as affected by light intensity using only color shade nets Color of nets Fruit mass (g) Seed mass (g) Seed number Exocarp (μm) Mesocarp (μm) Endocarp (μm) Pericarp (μm) Red 162.7a 4.10 a 208.33a 102.06b 6960.77a 36.17a 7099.00a Black 110.7b 3.48b 145.0b 107.80b 6333.36ab 31.66a 6472.82ab Pearl 148.5ab 3.62b 156.6b 126.37a 7055.47a 33.98a 7215.82a Blue 128.1ba 3.35b 131.33b 109.59b 6660.86b 31.84a 6802.29a ◙Open field 112.2b 3.20b 128.0b 85.95c 6081.07ab 35.46a 6202.48b ◙ Open field represent control Distinct letters in the row indicate significant differences according to Tukey’s test (P ≤ 0.05) This article is protected by copyright. All rights reserved Table 6: Content of lycopene and β-carotene (μg·g-1 fresh weight) in tomato fruits as affected by light intensity using color shade nets Lycopene β-carotene Color of Nets Plastic tunnel + color nets Only color nets Plastic tunnel + color nets Only color nets Red White Black Blue 64.89c 56.99b 57.91b 62.67c 55.00b 46.71a 61.46bc 59.87ab 2.01c 1.25a 1.33a 1.53b 1.67b 2.17c 1.73b 1.50b Control 48.89a◘ 48.10a◘ 1.61b◙ 2.25c◙ Control: ◘-plastic tunnel; Control: ◙-open field Distinct letters in the row indicate significant differences according to Tukey’s test (P ≤ 0.05) This article is protected by copyright. All rights reserved Table 7: Total acidity and total soluble solids contents in tomato fruits as affected by light intensity using color shade nets Total acidity % TSS % Total acidity % TSS % Color of nets Plastic tunnels + color nets Only color nets Red 0.34±0.02b 4.81±0.09b 0.37±0.02b 5.00±0.12ab Black 0.40±0.01a 5.18±0.07a 0.40±0.01a 5.06±0.05a White 0.38±0.01a 5.20±0.05a 0.36±0.01b 4.60±0.10c Blue 0.35±0.01b 5.23±0.08a 0.36±0.01b 4.55±0.09c Control 0.34±0.01b◘ 5.10±0.02a◘ 0.37±0.01b◙ 5.43±0.01a◙ Control: ◘-plastic tunnel Control: ◙-open field Distinct letters in the row indicate significant differences according to Tukey’s test (P ≤ 0.05) This article is protected by copyright. All rights reserved Table 8: Index of maturity and taste index in tomato fruits as affected by light intensity using color shade nets Index of maturity Taste index Color of Nets Plastic tunnel + color nets Only color nets Plastic tunnel + color nets Only color nets Red Black White Blue 14.15b 12.95c 13.68b 14.94a 13.51b 12.65b 12.78b 12.64b 1.05b 1.05b 1.06b 1.10a 1.04b 1.03b 1.00b 0.99b Control 15.00a◘ 14.68a◘ 1.09a◙ 1.10a◙ Control: ◘-plastic tunnel; Control: ◙-open field Distinct letters in the row indicate significant differences according to Tukey’s test (P ≤ 0.05) This article is protected by copyright. All rights reserved Fig. 1. Daily maximum and minimum temperatures over the period July 1st - August 30th for the 2009, 2010 and 2011 (data from meteorological station in Aleksinac)