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Effect of Colored Shading Screens on Plant Leaf Parameters and Tomato Fruit Quality.

Effect of Colored Shading Screens on Plant Leaf Parameters and Tomato Fruit Quality.

Study of Colored Shade Nets on Tomato Fruit

The concept of photoselective nets using commercial farming practices was studied in a summer tomato crop (Solanum lycopersicum ‘Vedetta’) in southern Serbia (under high solar radiation of 910 W m−², with a photosynthetic photon flux density of 1661 μmol m−² s−¹), under four different colored shade nets (pearl, red, blue, also black) providing 40% relative shade. The aim of the study was to determine how different environmental control technologies (colored shade nets as mesh greenhouses or plastic greenhouses integrated with colored shade nets) could influence plant parameters, yield, also tomato fruit quality grown in southern Serbia (Balkan region).

Results

Leaf Area Index (LAI) ranged from 4.6 to 5.8 in open field also plastic tunnels (control) with maximum LAI values of 7.9–8.2 in mesh greenhouses with red shade nets. Leaves grown under shade generally had a higher total chlorophyll and carotenoid content than control leaves. The pericarp thickness was significantly higher in tomato grow under pearl, red, and blue shade nets compared to other treatments and the control.

Conclusion: These results show that red and pearl photoselective nets create optimal growth conditions for plant development also produce fruits with thicker pericarp. Higher lycopene content, satisfactory taste index, and can be further implement within protect farming practices.

Keywords: Solanum lycopersicum; LAI, chlorophyll, carotenoids; pericarp thickness; lycopene; taste index.

tomato fruit quality
Shading induced an increase in LAI of about 40% compared to the open field.

Benefits for Tomato Fruit Quality

In traditional vegetable-producing regions, tomato cultivation in a protected environment has expanded to avoid fruit availability seasonality. Cost-effective protected cultivation, like plastic tunnels and mesh greenhouses, has the potential to reduce biotic stress. Moreover, photoselective shade nets increase the relative proportion of dispersed light and also absorb various spectral bands. Thus modifying the light environment. It is apply alone over mesh greenhouse structures or combine with greenhouse technologies. Mobile shading, applied only during sunny periods, is less detrimental than constant shading.

Climate for Tomato Fruit Quality

The climate in the southern Balkan regions is characterize by hot summers, high solar radiation, dry climate, also limited water resources. These stressful conditions require environmental control devices to enhance tomato production also quality. The use of shade nets has become very popular in Serbia over the past 2 years due to high temperatures (35–40 ∘C) in the summer season. High temperatures during the growing season are report to be detrimental to tomato growth, reproductive development, and production. Radiation is crucial as it supplies energy for photosynthesis, the basic production process in plants. Only radiation intercepted by the crop can contribute to photosynthesis.

Shading Benefits for Tomato Quality

Shading induced a 40% increase in LAI compared to open field. The reduction in LAI from 5.2 to 2.6 by removing old leaves did not affect yield. Differences in LAI between control (3.9 m² m−²) and shaded plants (4.7) increased in successive harvests. As shading degree increased, leaves developed a larger area per leaf, less weight per unit area, and per leaf. Chlorophyll content also photosynthetic capacity increase as shading degree increases. There are many studies available illustrating the beneficial effects of plant shading on tomato production also quality. Therefore, shading reduced tomato cracking appearance and eliminated sunburn on fruits.

Tomato Fruit Quality Depending on Chosen Net

Tomatoes produced under pearl shade nets retained good fruit quality also acceptable taste after post-harvest storage. Tomato production systems in colored mesh greenhouses need to be adjust to local climatic conditions before farmers can adopt this technology. This study is the first step in that direction. The aim of the study was to determine how different environmental control technologies (colored shade nets as mesh greenhouses or plastic greenhouses integrated with colored shade nets) could influence plant growth parameters, yield, and tomato fruit quality grown in southern Serbia (Balkan region).

Experimental

Plant Material and Cultivation

Shade nets were apply at the beginning of warm weather in early June. Colored nets were mounted on a structure about 2.2 m high above the plants (mesh greenhouse) or integrate with plastic greenhouse technologies (plastic tunnels covered by colored nets). Greenhouses were shade for the rest of the summer, and tomatoes were harvest until late August. A randomize block design with four treatments (red, blue, white, black, and control) was adopted. One-way ANOVA is perform using the SAS program, and means were compare using Tukey’s multiple range test. Plants were grow following the technique commonly implemented by producers. The substrate for seedling production consisted of 30% soil, 50% manure, 20% peat, and a small amount of marble.

Net Characteristics

To test the effect of shade nets (color and shading intensity), four different shade nets were use. Photoselective nets including ‘ColorNets’ (red, blue, and black) as well as ‘Neutral ColorNets’ (pearl) with a 40% relative shade intensity; photosynthetically active radiation (PAR) is compare with the open field microclimate and production. Color shade nets were obtain from Polysack Plastic Industries (Nir-Yitzhak, Israel) under the ChromatiNet trademark. These nets are unique because they spectrally modify and disperse transmitted light. Photoselective net products are based on the incorporation of various chromatic additives, light dispersing. And reflecting elements in the net materials during manufacturing.

Light Interception by Nets

The effect of nets on light interception was annually measure as a percentage of total PAR above the canopy, using a SunScan Ceptometer (SS1-UM-1.05; Delta-T Devices Ltd, Cambridge, UK) with a linearly arranged 64 photodiode sensor on a 100 cm long wand. Readings are in PAR quantum flux units (μmol m−² s−¹). All measurements were take on clear days at noon, every two days. The Solarimeter-SL 100 (KIMO Instruments, Edenbridge, UK) is a portable and easy-to-use solarimeter that measures solar irradiation range from 1 W m−² to 1300 W m−². All spectral data were expressed as the radiation intensity flux distribution in W m−² nm−¹.

Climate Measurement

Monthly meteorological data from May to September of 2009, 2010, and 2011 were use from meteorological stations in Aleksinac (Fig. 1).

Chlorophyll and Carotenoid Analysis

Chlorophyll a, b, and carotenoids were estimate in fresh leaf samples. Half a gram of fresh leaves was ground in acetone (90% v/v). Filtered, and made up to a final volume of 50 ml. Pigment concentrations [in mg g-¹ fresh weight (FW)] were calculate [absorbance (A) of the extract at 663, 648, and 470 nm] using the Lichtenthaler formula:

Chlorophyll a = [(11.75A663 − 2.35A645) × 50] ÷ 500

Chlorophyll b = [(18.21A645 − 3.93A663) × 50] ÷ 500

Carotenoids = [(1000A470 − 2.05 × Chlorophyll a − 114.8 × Chlorophyll b) × 50] ÷ 2140

Direct Methods for Leaf Area Determination

First, measure the length and width of the paper and calculate its surface area. Then determine its mass on the analytical balance. Next, remove the plant leaves, place them on paper, and trace their outlines with a pencil. The area marked on the paper is cut out with scissors, and its mass is determine (G1). Since the values of area, G, and G1 are know. The unknown leaf area (p1) can be calculate using the formula: p1/area = G1/G, so p1 = G1 × area/G.

Fruit Quality Measurements

Tomato samples (20 fruits) were collect each year from June to August from the third to the sixth floral branches. Each fruit was cut into pieces and homogenized in a conventional blender to obtain fruit juice. After that, the fruit juice was filtered using a Whatman No. 4 filter paper. And the filtrate was use to determine total soluble solids (TSS) and titratable acidity (TA). TSS was determine for each fruit sample in duplicate using a digital refractometer.

Extraction and Analysis of Pigments

Ground tomato fruit (8 g) was thoroughly mix with 40 ml of ethanol. The suspension was stirred until the tomato paste material was no longer sticky (approximately 3 minutes). Ethanol was removed by vacuum filtration. The retain tomato residue is mix with 60 ml of a mixture of acetone and petroleum ether (1:1). The extract is collect by vacuum filtration, and the filter residue is wash again with the solvent mixture (20 ml) to improve yield. The filtrate is transfer to a small separation funnel and mixed with 50 ml of saturated NaCl solution.

The organic layer is subsequently wash twice, first with 50 ml of 10% potassium carbonate and then with 50 ml of water. Finally, approximately 1 g of anhydrous magnesium sulfate is add to dry the organic layer. After 10-15 minutes, the solution was vacuum-filtered to remove the drying agent. Extracts (1 ml) with different concentrations were evaporated to dryness using vacuum rotary evaporators at room temperature, and the residues were dissolved in the mobile phase (acetonitrile:methanol:ethyl acetate, 6:2:2 v/v) at a concentration of 1 mg cm−³. The extracts were filtered through a 0.45 µm Millipore filter before analysis by high-performance liquid chromatography (HPLC).

The carotene and lycopene content of the tomato fruit is measure by HPLC (Agilent 1100 Series system; Agilent, New York, USA). A C18 reverse-phase column (4.6 x 250 mm, 5 μm, Zorbax; Agilent Co., New York, USA) was used for analysis, with 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 a diode array detector (Agilent 1200 Series) at a wavelength of 470 nm.

Light Microscopy

Slides for light microscopy were prepared according to standard procedures. Samples were fixed in formaldehyde-acetic acid-alcohol (FAA) for 24 hours, subsequently fixed in 70% ethanol, and dehydrated in graded ethanol series. After tissue impregnation in Histowax (56–58 ∘C), samples were embedded. After cooling the blocks on a cold plate and solidifying the paraffin, histological sections of approximately 5–7 µm were cut using a microtome (SM 2000 R; Leica, Wetzlar, Germany). Before staining, paraffin was removed from sections with xylene, followed by rehydration in graded ethanol series, after which the tissue was stained with safranin and alcian blue.

Statistical Analysis

All data were subject to one-way statistical analysis at P = 0.05 using JMP statistical analysis software (SAS Institute Inc., Cary, NC, USA), and mean values of all data are present.

RESULTS AND DISCUSSION

Microclimate Conditions

Shading nets are often deploy over crops to reduce heat stress. Our studies show that in July and August, with high insolation and reduced air circulation (13–15 h), the temperature under shading nets is 1∘C lower (pearl and red) and up to 3∘C lower (black) compared to open field (data not shown). Shading technology at various locations in Israel confirmed an overall decrease in daily maximum temperature (Tmax) by 1–5∘C, followed by an increase in maximum daily air relative humidity by approximately 3–10%. Shahak et al. reported that daily maximum temperature under shading nets (30% PAR) was up to 3∘C lower than control, similar to what Iglesias and Alegre have stated, and larger differences are record during bright and sunny days.

Leaf Area Index

In this study, we found that red and pearl shading nets significantly increase total leaf area compared to LAI values obtained from blue or black shading nets. Overall, tomato under plastic tunnels integrated with colored shading nets have a lower LAI compared to the LAI obtained under mesh greenhouses (only colored nets). Among the colored nets, black shading nets produce the crop with the lowest LAI value (Table 2). Leaf area indices varied from 4.6 in open field cultivation (control) to maximum LAI values of 8.2 in mesh greenhouses with red color shading nets (40% shade). Differences in LAI between control cultivation and shaded ones increased in successive harvests.

Crops grown under black shading nets had LAI values similar to control cultivation (Table 2). Lower light intensities increased stem elongation, leaf blade area, and leaf area index. Plants growing in shade tend to have a larger leaf area because cells expand more under low light intensity to be able to receive light for photosynthesis. Higher LAI values are generally indicative of excessive vegetative growth, which can delay the onset of fruit production. Plants acclimate to shade, in part, by increasing specific leaf area.

Chlorophyll Content

Shaded leaves have a higher total chlorophyll content (chlorophyll a and chlorophyll b) than control leaves (from greenhouse to open field). Plants from black shading nets have the highest chlorophyll content compared to other colored shading nets (Table 3). An increase in biomass (vegetative and reproductive) coincides with increases in leaf area and chlorophyll content. Leaves grown under shade harvest lower light levels; thus, they contain more chlorophyll than leaves exposed to direct sunlight. Even though leaves grown under shade are not directly expose to sunlight, they produce additional chlorophyll to capture diffuse radiation and produce the necessary carbohydrates for plant growth. Even if sun-exposed leaves contain less chlorophyll than shade-grown leaves.

The carotenoid content varied between 0.416 mg g-¹ in open field plants (control) and maximum carotenoid values in plants grown in mesh greenhouses with black nets (0.508 mg g-1) or blue nets (0.500 mg g-¹) (Table 3). A similar trend was observed in plastic tunnels integrated with colored shading nets where the lowest carotenoid content was recorded (0.380 mg g-¹). Tomato leaves grown under black and blue nets had significantly more total chlorophyll content than open field (control) or pearl shading net-grown leaves. Similarly, tomato plants grown under black, pearl, and blue nets had significantly more chlorophyll than leaves grown in a plastic tunnel (control) or under a plastic greenhouse integrated with red net.

Tomato Cultivation

Tomato plants grown in plastic tunnels (control) and under plastic tunnels integrated with red shading nets had a significantly lower carotenoid level than leaves grown under black, pearl, and blue nets. The chlorophyll a+b/carotenoid ratio increased in leaves grown under shade compared to control plants (open field or plastic tunnel). In terms of microclimate, it is likely to depend on air temperature, humidity, and day length, as all of these influence aspects of plant physiology related to fruit development and composition.

Fruit Physical Characteristics

Tomato fruit quality consists of pericarp and seeds. The elongated central placenta, with attached seeds, is made of parenchyma tissue and represents primary tissue, which then fills the locular cavities. Tomatoes grown under pearl nets had most of the fruit as pericarp, relative to the total fruit mass. Tomato from 40% shade pearl nets had most of the fruit as pericarp (80.9%), with locular gel tissues (16.5%) and seeds (2.6%) contributing to the rest of the total fruit mass. Statistically confirmed differences exist in mesocarp and gelatinous mass percentages with treatment. Seed number (n=208) and mass (5.4 g) were consistently and significantly higher in fruits grown in a red net greenhouse compared to control (Table 4 and Table 5).

Tomato Fruit Quality

The number of seeds per fruit in autumn cultivation correlated with fruit weight and volume. However, another study indicated that no such correlation was observed in summer cultivation. In summer, fruits have fewer seeds per fruit than in autumn, because pollination and fertilization are restrict by high temperatures and low relative humidity inside the greenhouse at that time, while higher autumn humidity favors fertilization. Rylski et al. reported that temperature and irradiation conditions in the early stages of flower development are important factors determining tomato fruit quality and production. Low temperature prevents fertilization, and thus decreases fruiting, but low irradiation causes swelling and blotchy ripening.

Importance of Lycopene

Most quality traits show continuous variation, strongly influenced by environmental conditions. Lycopene is the most abundant carotenoid in ripe tomato, representing approximately 80–90% of total pigments. Tomatoes exposed to sunlight in the field often develop poor color, because exposed fruits have low lycopene content.

Total Soluble Solids and Titratable Acidity

Light intensity and temperature have a significant impact on sugar accumulation in tomatoes. Fruit exposure to high temperatures, especially during fruit cell division and ripening, resulted in an increase in TSS. The TSS content in tomatoes mainly consists of reducing sugars. The observed TSS content in fruits analyzed in this work ranged between 4.55 and 5.43∘Brix. We found a TSS content of 5.43 and 5.10∘Brix for tomatoes grown in the field and in a plastic greenhouse, respectively. No significant differences were observ in TSS values of fruits grow under control conditions (plastic greenhouse) and fruits grow in plastic greenhouses integrate with different shading nets (Table 7).

CONCLUSIONS

Our results show that applying shade from colored nets to tomatoes 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. Photoselective and light-dispersing shading nets emerge as interesting tools that can be further implement within protect cultivation practices.

table of photosynthetically active solar radiation reduction under different colored meshes
Table 1. Reduction of solar radiation and photosynthetically active radiation (PAR), over the tomato canopy measured at noon on a sunny day (July 20) under shading nets of different colors.

Data are reproduce from Ili • and Milenkovi • PT, plastic tunnel. Controls: * plastic tunnel (solar radiation, 761 W m−²); † open field (full sunlight exposure, 910 W m−²).

tomato fruit quality
Table 2. Leaf area index in a crop affected by light intensity using colored shading screens

Controls: * plastic tunnel; † open field. Different superscript letters in the row indicate significant differences according to Tukey’s test (P ≤0.05).

table photosynthetic pigments in tomato at colored light intensity
Table 3. Photosynthetic pigments (mg g-¹ ) in leaves of tomato plants in response to light intensity using colored shading meshes

Controls: * plastic tunnel; † open field. Different superscript letters in the row indicate significant differences according to Tukey’s test (P ≤0.05). Car, carotenoids; Chl, chlorophyll.

tomato fruit quality
Table 4. Structural characteristics of tomato fruit as affected by light intensity using plastic tunnels and colored shading meshes.

*Plastic tunnel represents the control. Different superscript letters in the row indicate significant differences according to Tukey’s test (P ≤0.05).

structural characteristics of tomato using only colored meshes
Table 5. Structural characteristics of tomato fruit as affected by light intensity using only colored shading nets.

†Open field represents the control. Different superscript letters in the row indicate significant differences according to Tukey’s test (P ≤0.05).

tomato fruit quality
Table 6. Lycopene and ?-carotene content (μg g-1 fresh weight) in tomato fruits as affected by light intensity when using colored shading nets.

Controls: * plastic tunnel; † open field. Different superscript letters in the row indicate significant differences according to Tukey’s test (P ≤0.05).

Total acidity
Table 7. Total acidity and total soluble solids content (TSS) in tomato fruit as affect by light intensity when color shading nets were use.

Controls: * plastic tunnel; † open field. Different superscript letters in the row indicate significant differences according to Tukey’s test (P ≤0.05).

tomato fruit quality
Table 8. Maturity index and flavor index in tomato fruit as affected by light intensity using colored shading nets.

Controls: * plastic tunnel; † open field. Different superscript letters in the row indicate significant differences according to Tukey’s test (P ≤0.05).

Maximum temperatures
Figure 1. Daily maximum and minimum temperatures during the period from July 1 to August 30 for the years 2009, 2010 and 2011 (data from the meteorological station in Aleksinac).

Fill out the form below to let us know your questions or comments:

Study of Colored Shade Nets on Tomato Fruit

The concept of photoselective nets using commercial farming practices was studied in a summer tomato crop (Solanum lycopersicum ‘Vedetta’) in southern Serbia (under high solar radiation of 910 W m−², with a photosynthetic photon flux density of 1661 μmol m−² s−¹), under four different colored shade nets (pearl, red, blue, also black) providing 40% relative shade. The aim of the study was to determine how different environmental control technologies (colored shade nets as mesh greenhouses or plastic greenhouses integrated with colored shade nets) could influence plant parameters, yield, also tomato fruit quality grown in southern Serbia (Balkan region).

Results

Leaf Area Index (LAI) ranged from 4.6 to 5.8 in open field also plastic tunnels (control) with maximum LAI values of 7.9–8.2 in mesh greenhouses with red shade nets. Leaves grown under shade generally had a higher total chlorophyll and carotenoid content than control leaves. The pericarp thickness was significantly higher in tomato grow under pearl, red, and blue shade nets compared to other treatments and the control.

Conclusion: These results show that red and pearl photoselective nets create optimal growth conditions for plant development also produce fruits with thicker pericarp. Higher lycopene content, satisfactory taste index, and can be further implement within protect farming practices.

Keywords: Solanum lycopersicum; LAI, chlorophyll, carotenoids; pericarp thickness; lycopene; taste index.

tomato fruit quality
Shading induced an increase in LAI of about 40% compared to the open field.

Benefits for Tomato Fruit Quality

In traditional vegetable-producing regions, tomato cultivation in a protected environment has expanded to avoid fruit availability seasonality. Cost-effective protected cultivation, like plastic tunnels and mesh greenhouses, has the potential to reduce biotic stress. Moreover, photoselective shade nets increase the relative proportion of dispersed light and also absorb various spectral bands. Thus modifying the light environment. It is apply alone over mesh greenhouse structures or combine with greenhouse technologies. Mobile shading, applied only during sunny periods, is less detrimental than constant shading.

Climate for Tomato Fruit Quality

The climate in the southern Balkan regions is characterize by hot summers, high solar radiation, dry climate, also limited water resources. These stressful conditions require environmental control devices to enhance tomato production also quality. The use of shade nets has become very popular in Serbia over the past 2 years due to high temperatures (35–40 ∘C) in the summer season. High temperatures during the growing season are report to be detrimental to tomato growth, reproductive development, and production. Radiation is crucial as it supplies energy for photosynthesis, the basic production process in plants. Only radiation intercepted by the crop can contribute to photosynthesis.

Shading Benefits for Tomato Quality

Shading induced a 40% increase in LAI compared to open field. The reduction in LAI from 5.2 to 2.6 by removing old leaves did not affect yield. Differences in LAI between control (3.9 m² m−²) and shaded plants (4.7) increased in successive harvests. As shading degree increased, leaves developed a larger area per leaf, less weight per unit area, and per leaf. Chlorophyll content also photosynthetic capacity increase as shading degree increases. There are many studies available illustrating the beneficial effects of plant shading on tomato production also quality. Therefore, shading reduced tomato cracking appearance and eliminated sunburn on fruits.

Tomato Fruit Quality Depending on Chosen Net

Tomatoes produced under pearl shade nets retained good fruit quality also acceptable taste after post-harvest storage. Tomato production systems in colored mesh greenhouses need to be adjust to local climatic conditions before farmers can adopt this technology. This study is the first step in that direction. The aim of the study was to determine how different environmental control technologies (colored shade nets as mesh greenhouses or plastic greenhouses integrated with colored shade nets) could influence plant growth parameters, yield, and tomato fruit quality grown in southern Serbia (Balkan region).

Experimental

Plant Material and Cultivation

Shade nets were apply at the beginning of warm weather in early June. Colored nets were mounted on a structure about 2.2 m high above the plants (mesh greenhouse) or integrate with plastic greenhouse technologies (plastic tunnels covered by colored nets). Greenhouses were shade for the rest of the summer, and tomatoes were harvest until late August. A randomize block design with four treatments (red, blue, white, black, and control) was adopted. One-way ANOVA is perform using the SAS program, and means were compare using Tukey’s multiple range test. Plants were grow following the technique commonly implemented by producers. The substrate for seedling production consisted of 30% soil, 50% manure, 20% peat, and a small amount of marble.

Net Characteristics

To test the effect of shade nets (color and shading intensity), four different shade nets were use. Photoselective nets including ‘ColorNets’ (red, blue, and black) as well as ‘Neutral ColorNets’ (pearl) with a 40% relative shade intensity; photosynthetically active radiation (PAR) is compare with the open field microclimate and production. Color shade nets were obtain from Polysack Plastic Industries (Nir-Yitzhak, Israel) under the ChromatiNet trademark. These nets are unique because they spectrally modify and disperse transmitted light. Photoselective net products are based on the incorporation of various chromatic additives, light dispersing. And reflecting elements in the net materials during manufacturing.

Light Interception by Nets

The effect of nets on light interception was annually measure as a percentage of total PAR above the canopy, using a SunScan Ceptometer (SS1-UM-1.05; Delta-T Devices Ltd, Cambridge, UK) with a linearly arranged 64 photodiode sensor on a 100 cm long wand. Readings are in PAR quantum flux units (μmol m−² s−¹). All measurements were take on clear days at noon, every two days. The Solarimeter-SL 100 (KIMO Instruments, Edenbridge, UK) is a portable and easy-to-use solarimeter that measures solar irradiation range from 1 W m−² to 1300 W m−². All spectral data were expressed as the radiation intensity flux distribution in W m−² nm−¹.

Climate Measurement

Monthly meteorological data from May to September of 2009, 2010, and 2011 were use from meteorological stations in Aleksinac (Fig. 1).

Chlorophyll and Carotenoid Analysis

Chlorophyll a, b, and carotenoids were estimate in fresh leaf samples. Half a gram of fresh leaves was ground in acetone (90% v/v). Filtered, and made up to a final volume of 50 ml. Pigment concentrations [in mg g-¹ fresh weight (FW)] were calculate [absorbance (A) of the extract at 663, 648, and 470 nm] using the Lichtenthaler formula:

Chlorophyll a = [(11.75A663 − 2.35A645) × 50] ÷ 500

Chlorophyll b = [(18.21A645 − 3.93A663) × 50] ÷ 500

Carotenoids = [(1000A470 − 2.05 × Chlorophyll a − 114.8 × Chlorophyll b) × 50] ÷ 2140

Direct Methods for Leaf Area Determination

First, measure the length and width of the paper and calculate its surface area. Then determine its mass on the analytical balance. Next, remove the plant leaves, place them on paper, and trace their outlines with a pencil. The area marked on the paper is cut out with scissors, and its mass is determine (G1). Since the values of area, G, and G1 are know. The unknown leaf area (p1) can be calculate using the formula: p1/area = G1/G, so p1 = G1 × area/G.

Fruit Quality Measurements

Tomato samples (20 fruits) were collect each year from June to August from the third to the sixth floral branches. Each fruit was cut into pieces and homogenized in a conventional blender to obtain fruit juice. After that, the fruit juice was filtered using a Whatman No. 4 filter paper. And the filtrate was use to determine total soluble solids (TSS) and titratable acidity (TA). TSS was determine for each fruit sample in duplicate using a digital refractometer.

Extraction and Analysis of Pigments

Ground tomato fruit (8 g) was thoroughly mix with 40 ml of ethanol. The suspension was stirred until the tomato paste material was no longer sticky (approximately 3 minutes). Ethanol was removed by vacuum filtration. The retain tomato residue is mix with 60 ml of a mixture of acetone and petroleum ether (1:1). The extract is collect by vacuum filtration, and the filter residue is wash again with the solvent mixture (20 ml) to improve yield. The filtrate is transfer to a small separation funnel and mixed with 50 ml of saturated NaCl solution.

The organic layer is subsequently wash twice, first with 50 ml of 10% potassium carbonate and then with 50 ml of water. Finally, approximately 1 g of anhydrous magnesium sulfate is add to dry the organic layer. After 10-15 minutes, the solution was vacuum-filtered to remove the drying agent. Extracts (1 ml) with different concentrations were evaporated to dryness using vacuum rotary evaporators at room temperature, and the residues were dissolved in the mobile phase (acetonitrile:methanol:ethyl acetate, 6:2:2 v/v) at a concentration of 1 mg cm−³. The extracts were filtered through a 0.45 µm Millipore filter before analysis by high-performance liquid chromatography (HPLC).

The carotene and lycopene content of the tomato fruit is measure by HPLC (Agilent 1100 Series system; Agilent, New York, USA). A C18 reverse-phase column (4.6 x 250 mm, 5 μm, Zorbax; Agilent Co., New York, USA) was used for analysis, with 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 a diode array detector (Agilent 1200 Series) at a wavelength of 470 nm.

Light Microscopy

Slides for light microscopy were prepared according to standard procedures. Samples were fixed in formaldehyde-acetic acid-alcohol (FAA) for 24 hours, subsequently fixed in 70% ethanol, and dehydrated in graded ethanol series. After tissue impregnation in Histowax (56–58 ∘C), samples were embedded. After cooling the blocks on a cold plate and solidifying the paraffin, histological sections of approximately 5–7 µm were cut using a microtome (SM 2000 R; Leica, Wetzlar, Germany). Before staining, paraffin was removed from sections with xylene, followed by rehydration in graded ethanol series, after which the tissue was stained with safranin and alcian blue.

Statistical Analysis

All data were subject to one-way statistical analysis at P = 0.05 using JMP statistical analysis software (SAS Institute Inc., Cary, NC, USA), and mean values of all data are present.

RESULTS AND DISCUSSION

Microclimate Conditions

Shading nets are often deploy over crops to reduce heat stress. Our studies show that in July and August, with high insolation and reduced air circulation (13–15 h), the temperature under shading nets is 1∘C lower (pearl and red) and up to 3∘C lower (black) compared to open field (data not shown). Shading technology at various locations in Israel confirmed an overall decrease in daily maximum temperature (Tmax) by 1–5∘C, followed by an increase in maximum daily air relative humidity by approximately 3–10%. Shahak et al. reported that daily maximum temperature under shading nets (30% PAR) was up to 3∘C lower than control, similar to what Iglesias and Alegre have stated, and larger differences are record during bright and sunny days.

Leaf Area Index

In this study, we found that red and pearl shading nets significantly increase total leaf area compared to LAI values obtained from blue or black shading nets. Overall, tomato under plastic tunnels integrated with colored shading nets have a lower LAI compared to the LAI obtained under mesh greenhouses (only colored nets). Among the colored nets, black shading nets produce the crop with the lowest LAI value (Table 2). Leaf area indices varied from 4.6 in open field cultivation (control) to maximum LAI values of 8.2 in mesh greenhouses with red color shading nets (40% shade). Differences in LAI between control cultivation and shaded ones increased in successive harvests.

Crops grown under black shading nets had LAI values similar to control cultivation (Table 2). Lower light intensities increased stem elongation, leaf blade area, and leaf area index. Plants growing in shade tend to have a larger leaf area because cells expand more under low light intensity to be able to receive light for photosynthesis. Higher LAI values are generally indicative of excessive vegetative growth, which can delay the onset of fruit production. Plants acclimate to shade, in part, by increasing specific leaf area.

Chlorophyll Content

Shaded leaves have a higher total chlorophyll content (chlorophyll a and chlorophyll b) than control leaves (from greenhouse to open field). Plants from black shading nets have the highest chlorophyll content compared to other colored shading nets (Table 3). An increase in biomass (vegetative and reproductive) coincides with increases in leaf area and chlorophyll content. Leaves grown under shade harvest lower light levels; thus, they contain more chlorophyll than leaves exposed to direct sunlight. Even though leaves grown under shade are not directly expose to sunlight, they produce additional chlorophyll to capture diffuse radiation and produce the necessary carbohydrates for plant growth. Even if sun-exposed leaves contain less chlorophyll than shade-grown leaves.

The carotenoid content varied between 0.416 mg g-¹ in open field plants (control) and maximum carotenoid values in plants grown in mesh greenhouses with black nets (0.508 mg g-1) or blue nets (0.500 mg g-¹) (Table 3). A similar trend was observed in plastic tunnels integrated with colored shading nets where the lowest carotenoid content was recorded (0.380 mg g-¹). Tomato leaves grown under black and blue nets had significantly more total chlorophyll content than open field (control) or pearl shading net-grown leaves. Similarly, tomato plants grown under black, pearl, and blue nets had significantly more chlorophyll than leaves grown in a plastic tunnel (control) or under a plastic greenhouse integrated with red net.

Tomato Cultivation

Tomato plants grown in plastic tunnels (control) and under plastic tunnels integrated with red shading nets had a significantly lower carotenoid level than leaves grown under black, pearl, and blue nets. The chlorophyll a+b/carotenoid ratio increased in leaves grown under shade compared to control plants (open field or plastic tunnel). In terms of microclimate, it is likely to depend on air temperature, humidity, and day length, as all of these influence aspects of plant physiology related to fruit development and composition.

Fruit Physical Characteristics

Tomato fruit quality consists of pericarp and seeds. The elongated central placenta, with attached seeds, is made of parenchyma tissue and represents primary tissue, which then fills the locular cavities. Tomatoes grown under pearl nets had most of the fruit as pericarp, relative to the total fruit mass. Tomato from 40% shade pearl nets had most of the fruit as pericarp (80.9%), with locular gel tissues (16.5%) and seeds (2.6%) contributing to the rest of the total fruit mass. Statistically confirmed differences exist in mesocarp and gelatinous mass percentages with treatment. Seed number (n=208) and mass (5.4 g) were consistently and significantly higher in fruits grown in a red net greenhouse compared to control (Table 4 and Table 5).

Tomato Fruit Quality

The number of seeds per fruit in autumn cultivation correlated with fruit weight and volume. However, another study indicated that no such correlation was observed in summer cultivation. In summer, fruits have fewer seeds per fruit than in autumn, because pollination and fertilization are restrict by high temperatures and low relative humidity inside the greenhouse at that time, while higher autumn humidity favors fertilization. Rylski et al. reported that temperature and irradiation conditions in the early stages of flower development are important factors determining tomato fruit quality and production. Low temperature prevents fertilization, and thus decreases fruiting, but low irradiation causes swelling and blotchy ripening.

Importance of Lycopene

Most quality traits show continuous variation, strongly influenced by environmental conditions. Lycopene is the most abundant carotenoid in ripe tomato, representing approximately 80–90% of total pigments. Tomatoes exposed to sunlight in the field often develop poor color, because exposed fruits have low lycopene content.

Total Soluble Solids and Titratable Acidity

Light intensity and temperature have a significant impact on sugar accumulation in tomatoes. Fruit exposure to high temperatures, especially during fruit cell division and ripening, resulted in an increase in TSS. The TSS content in tomatoes mainly consists of reducing sugars. The observed TSS content in fruits analyzed in this work ranged between 4.55 and 5.43∘Brix. We found a TSS content of 5.43 and 5.10∘Brix for tomatoes grown in the field and in a plastic greenhouse, respectively. No significant differences were observ in TSS values of fruits grow under control conditions (plastic greenhouse) and fruits grow in plastic greenhouses integrate with different shading nets (Table 7).

CONCLUSIONS

Our results show that applying shade from colored nets to tomatoes 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. Photoselective and light-dispersing shading nets emerge as interesting tools that can be further implement within protect cultivation practices.

table of photosynthetically active solar radiation reduction under different colored meshes
Table 1. Reduction of solar radiation and photosynthetically active radiation (PAR), over the tomato canopy measured at noon on a sunny day (July 20) under shading nets of different colors.

Data are reproduce from Ili • and Milenkovi • PT, plastic tunnel. Controls: * plastic tunnel (solar radiation, 761 W m−²); † open field (full sunlight exposure, 910 W m−²).

tomato fruit quality
Table 2. Leaf area index in a crop affected by light intensity using colored shading screens

Controls: * plastic tunnel; † open field. Different superscript letters in the row indicate significant differences according to Tukey’s test (P ≤0.05).

table photosynthetic pigments in tomato at colored light intensity
Table 3. Photosynthetic pigments (mg g-¹ ) in leaves of tomato plants in response to light intensity using colored shading meshes

Controls: * plastic tunnel; † open field. Different superscript letters in the row indicate significant differences according to Tukey’s test (P ≤0.05). Car, carotenoids; Chl, chlorophyll.

tomato fruit quality
Table 4. Structural characteristics of tomato fruit as affected by light intensity using plastic tunnels and colored shading meshes.

*Plastic tunnel represents the control. Different superscript letters in the row indicate significant differences according to Tukey’s test (P ≤0.05).

structural characteristics of tomato using only colored meshes
Table 5. Structural characteristics of tomato fruit as affected by light intensity using only colored shading nets.

†Open field represents the control. Different superscript letters in the row indicate significant differences according to Tukey’s test (P ≤0.05).

tomato fruit quality
Table 6. Lycopene and ?-carotene content (μg g-1 fresh weight) in tomato fruits as affected by light intensity when using colored shading nets.

Controls: * plastic tunnel; † open field. Different superscript letters in the row indicate significant differences according to Tukey’s test (P ≤0.05).

Total acidity
Table 7. Total acidity and total soluble solids content (TSS) in tomato fruit as affect by light intensity when color shading nets were use.

Controls: * plastic tunnel; † open field. Different superscript letters in the row indicate significant differences according to Tukey’s test (P ≤0.05).

tomato fruit quality
Table 8. Maturity index and flavor index in tomato fruit as affected by light intensity using colored shading nets.

Controls: * plastic tunnel; † open field. Different superscript letters in the row indicate significant differences according to Tukey’s test (P ≤0.05).

Maximum temperatures
Figure 1. Daily maximum and minimum temperatures during the period from July 1 to August 30 for the years 2009, 2010 and 2011 (data from the meteorological station in Aleksinac).

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