influence of cluster thinning on quantitative and qualitative · significance of this study what is...

30 E u r o p e a n J o u r n a l o f H o r t i c u l t u r a l S c i e n c e

Eur. J. Hortic. Sci. 85(1), 30–41 | ISSN 1611-4426 print, 1611-4434 online | https://doi.org/10.17660/eJHS.2020/85.1.4 | © ISHS 2020

Influence of cluster thinning on quantitative and qualitative parameters of cherry tomatoA. Slatnar, M. Mikulic-Petkovsek, F. Stampar, R. Veberic and N. Kacjan MarsicAgronomy Department, Chair for Fruit, Wine and Vegetable Growing, Biotechnical Faculty, University of Ljubljana, Ljubljana, Slovenia

Original articleGerman Society for Horticultural Science

SummaryThe practice of cherry tomato cluster thinning

may contribute to increased quality of the remaining fruit. The objective of our study was to evaluate se-lected quality traits and the content of primary and secondary metabolites in fruits of cherry tomato subjected to two fruit thinning intensities (thinned to ½ or to 2∕₃ of the initial cluster length). Cluster thinning induced higher fruit yield at the beginning of the harvest period, between 98 and 115 days after transplanting (DAT). On later samplings, the yield of the control plants increased and remained high-er until the end of the experiment, which resulted in higher total yield of control plants. Both thinning treatments significantly increased average mass of fruits from the distal cluster section in comparison to the control treatment. Redder fruits with signifi-cantly higher a*/b* ratio were characteristic for the proximal and distal sections of the control clusters in comparison to the fruits from the thinning treat-ments. Tomato cluster thinning caused periods with no yield between 117 and 128 DAT and between 142 and 152 DAT during the harvest period. Moreover, cluster-thinned tomatoes accumulated less sugar and more organic acids than the control fruit. The content of total analyzed carotenoids was comparable be-tween cluster-thinned and control fruit. Regardless of the treatment, 22 individual phenolic compounds from four phenolic groups have been identified in cherry tomato fruit. Significant differences among treatments have been determined in approximately one half of analyzed phenolics, particularly from the group of hydroxycinnamic acids. It can be concluded that cluster thinning only moderately affected sec-ondary metabolite composition of cherry tomato and had little positive effect on the levels of the two most important groups of antioxidant compounds (phe-nols and carotenoids).

Keywordscarotenoids, cherry tomato, cluster thinning, fruit quality, phenolic compounds

Significance of this studyWhat is already known on this subject?• Cluster thinning is a common measure in greenhouse

tomato production aimed to maximize tomato fruit size, while no information about the fruit load adaptability to the production of assimilate after the cluster thinning of cherry tomatoes currently exists.

What are the new findings?• Cluster thinning influenced harvest time, yield and

color of cherry tomatoes, as well as the composition of sugars, organic acids, carotenoids and phenolic compounds in different ways.

What is the expected impact on horticulture?• To widen horticultural knowledge about the

advantages and disadvantages of cluster thinning of cherry tomato.

IntroductionCherry tomato varieties are gaining consumer’s popular-

ity in comparison with larger fruited tomatoes, mainly due to their higher levels of sugars, dry matter, and soluble sol-ids, which result in a sweeter flavor (Raffo et al., 2002). Most cherry tomato varieties are quite vigorous and produce more fruit per stem in comparison to larger fruited (common) to-

mato varieties. Moreover, the levels of compounds with nu-tritional and functional relevance are higher in cherry toma-toes compared to common varieties (Figas et al., 2015).

The fruits of cherry tomato varieties can be picked indi-vidually or as a whole cluster. Each cluster can contain be-tween 12 and 50 fruits, which depends above all on the vari-ety. When there are many fruits in the cluster, some irregular growth and ripening may occur. Fruits located in the prox-imal section of the cluster ripen prior to those in the distal section (Gautier et al., 2005; Mikulic-Petkovsek et al., 2016). Moreover, fruit mass of cherry tomatoes located in the distal section of the cluster is lower to fruit mass of tomatoes in the proximal section. This is in direct correlation with a higher cell number in proximal section as has been demonstrated in some tomato and pear varieties (Cheniclet et al., 2005; Gautier et al., 2005; Zhang et al., 2006).

The functional quality of food is determined by its ability to accumulate bioactive health-promoting compounds. To-mato mainly contains carotenoids (lycopene, ß-carotene and some colourless carotenoids such as phytoene and phytoflu-ene) (Cortes-Olmos et al., 2014), phenolic compounds (chlo-rogenic acids and quercetin) (Siddiqui et al., 2015), vitamin C and tocopherols (Ripoll et al., 2016).

Concentrations of primary and secondary compounds in tomatoes are known to depend on factors like the variety, de-velopmental stage, agricultural practices and environmental conditions (Huang et al., 2016). However, other important quality traits of tomato fruit, such as size, shape and fruit colour, are strongly influenced also by the number of fruits per cluster and the position of fruit in the cluster (Kasim and Kasim, 2015).

V o l u m e 8 5 | I s s u e 1 | F e b r u a r y 2 0 2 0 31

Slatnar et al. | Influence of cluster thinning on quantitative and qualitative parameters of cherry tomato

The number of fruits per cluster and fruit size of stan-dard fruited (common) tomato varieties are regulated with thinning. In cherry tomato, uniformity of fruit size can also be improved by removing surplus fruits; thereby adapting the fruit load to the production of assimilates (Field and Nichols, 2004). The practice of fruit thinning is a measure that might contribute to increased fruit quality and quantity of cherry tomato. The aim of this research was therefore to evaluate quality characteristics of cherry tomato subjected to two different thinning intensities (thinned to ½ or 2∕₃ of the initial cluster length). We hypothesized that cluster thin-ning influences the internal quality of cherry tomato, and at the same time modifies fruit yield. Based on our knowledge, the impact of cluster thinning on selected quality parameters and cherry tomato fruit yield have not been investigated to the present day.

Materials and methods

Plant materialFruits of cherry tomato (Solanum lycopersicum L.) ‘Saku-

ra F1’ were collected from hydroponically grown plants. The experiment was conducted from April to September on the experimental field (latitude 46.05N, longitude 11.47E, al-titude 289 m) of the Biotechnical Faculty in Ljubljana, Slo-venia. On March 10th, cherry tomato seeds were sown in a peat substrate (Klasmann N3) to a plug tray system. Thirty days after sowing, the transplants with two true leaves were transplanted in rock wool cubes (10 × 10 × 7.5 cm) and irri-gated with 50% Resh’s nutrient solution. Fourteen days after transplanting (DAT), well-developed transplants were placed on rock wool slabs (100 × 20 × 7.5 cm, Grodan B.V., Master type, The Netherlands) trained to one stem and tied up with strings to a high wire system. At the end of June (76 DAT) three cluster thinning treatments were initiated. In the first treatment clusters of cherry tomato were thinned to one half

(½) of the initial cluster length, in the second treatment clus-ters were thinned to 2∕₃ of the initial cluster length and con-trol clusters were not thinned at all. Thinning was performed once or twice per week until the beginning of September. The experiment was performed in a randomized block de-sign, with four replications. In each replication, the thinning treatments were randomly arranged. A single plot contained 6 plants, grown on 2 parallel rows of rock wool slabs at the density of 1.67 plants m-2. During the growing period, until the end of September, tomato plants were supplied with a moderate nutrient solution for tomatoes (Resh, 1995), with the following concentration of nutrients (in mg L-1): N-NO3 – 196, N-NH4 – 14; P – 31, K – 234, Ca – 160, Mg – 48, Fe – 0.84, Mn – 0.55, B – 0.33, Zn – 0.33, Cu – 0.05, Mo – 0.05. The EC of nutrient solution was 2.8 ± 0.2 dS m-1, and pH of nutrient solution was adjusted to 5.50 by adding diluted nitric acid.

During the entire growing period, a low number of leaves (approximately 13 to 15) was kept in plants from the thinning treatments and a high number (approximately 15 to 17) in plants from the control treatment, to prevent cuticle cracking (Dorais et al., 2010). Cherry tomatoes were hand-harvested when all fruits in an individual cluster were fully ripe, which is a common harvesting practice for the ‘Sakura F1’ variety. The first harvest was performed 98 DAT and harvest lasted until seven clusters were fully ripe on each plant, this was 163 DAT (until the end of September). At each harvest, the number of fruit per cluster and cluster mass were recorded. In the second decade of August (when the fourth level of to-mato clusters was ripe), three undamaged fruits were select-ed for each thinning treatment, replication and cluster part (proximal, middle and distal); together we had 108 fruits for chemical analysis. Variations in carpometric characteristics (fruit mass, color), and the content of sugars, organic acids, and ascorbic acid, as well as of carotenoids and phenolic compounds were studied on these samples.

11

FIGURE 1. Average daily air temperature (°C) and total daily solar irradiation (MJ m-2) during the cherry tomato growing period from March to September. The main experimental actions are marked with arrows.

Figure 1. Average daily air temperature (°C) and total daily solar irradiation (MJ m-2) during the cherry tomato growing period from March to September. The main experimental actions are marked with arrows.



Weather conditionsAverage daily temperature and total daily solar irradia-

tion (Figure 1) were recorded during the experimental pe-riod from March to September at the meteorological station located on the experimental field of the Biotechnical Facul-ty in Ljubljana, Slovenia. Environmental conditions in the greenhouse were very similar to those in the open field but, based on experience from previous years, the temperature was 3 to 4°C higher. The weather during the experimental period was comparable to the long-term average in terms of temperatures. The highest temperatures compared to the long-term average (more than 3°C higher) were measured in April, May, August and September. Higher solar irradiation was also recorded during the experimental period compared to the long-term average.

Measurement of CIELAB colour valuesSkin colour variables were measured using a portable col-

orimeter (CR-10 Chroma; Minolta Co., Osaka, Japan) with C illuminant. Fruit chromaticity was expressed in L*, a*, b*, C* and h° colour space coordinates (CIELAB). Hue (h°) and chro-ma (C*) were calculated from L*, a*, and b* values (McGuire, 1992). Colour was described by the a*/b* index, frequently used as a reference for maturity stages evaluation of vine-rip-ened fruits (Raffo et al., 2002). Four measurements were re-corded on the equatorial region of each sampled fruit (all fruit from the analysed clusters) and mean value was calculated.

Sugars, organic acids and ascorbic acid extraction and determination

The content of carbohydrates (sucrose, glucose and fruc-tose) and organic acids (malic and citric) was performed as described by Slatnar et al. (2012), with slight modifications. Three fruits per individual treatment (in four repetitions) were mashed to a pulp and 10 g were immersed in 25 mL of double distilled water and homogenised with a T-25 Ul-tra-Turrax (IKA®– Labortechnik, Staufen, Germany). All com-pounds were identified by a high-performance liquid chro-matography (HPLC; Thermo Scientific, Finnigan Spectra Sys-tem, Waltham, MA, USA) described by Slatnar et al. (2012).

Extraction of ascorbic acid was carried out using the same procedure except that 2.5 g of the pulp was extracted with 5 mL of 2% metaphosphoric acid. Samples were left at room temperature for 30 min on an orbital shaking platform (Grant-Bio POS-300, Grant Instruments, Shepreth, England), centrifuged (Eppendorf 5810 R Centrifuge, Hamburg, Ger-many) at 10,000 rpm for 5 min at 4°C and filtered through a 0.20 µm cellulose mixed ester filter Chromafil A-20/25 (Macherey-Nagel, Düren, Germany) into vials. Samples were analysed using a Thermo Finnigan Surveyor HPLC system (Thermo Scientific, Finnigan Spectra System, Waltham, MA, USA). The chromatographic conditions for ascorbic acid de-termination were the same as for the organic acids, except that the column temperature was set to 20°C, and the UV de-tector at 245 nm.

Quantification was assessed from peak areas and calcu-lated by the use of a calibration curve of corresponding stan-dards. Concentrations were expressed on a fresh mass basis in g kg-1 (sugar/organic acid) and mg kg-1 (ascorbic acid).

Extraction and determination of carotenoidsFor the extraction of carotenoids, the method previous-

ly described by Orazem et al. (2013) was used. One gram of cherry tomato pulp was placed in a round-bottomed centri-fuge tube, wrapped in aluminium foil to prevent light access,

and homogenized with 2 mL of cold ethanol for 3 min using a T-25 Ultra-Turax (IKA®– Labortechnik, Staufen, Germany) at 8,400 rpm. Eight mL of hexane were added, and the sample was homogenized for 2 min at 8,400 rpm. The homogenate was then centrifuged for 4 min at 10,000 rpm and 4°C. The hexane layer was transferred to an Erlenmeyer flask with a pipette, flushed with nitrogen, sealed and kept in the ab-sence of light. 5 mL of saturated sodium chloride was add-ed to the contents of the centrifuge tube. The mixture was stirred gently until homogenized. Afterwards, another 8 mL of hexane was added to the mixture, homogenized for 2 min with an Ultra-Turax (IKA®– Labortechnik, Staufen, Germany) at 3,800 rpm and centrifuged as described previously. The process was repeated once more and all hexane layers were combined in the Erlenmeyer flask. The extraction phases were performed in a cooled room (12°C) with dimmed light conditions. Saponification of the carotenoid-bearing hexane and HPLC determination were performed according to the method described by Orazem et al. (2013).

Extraction and determination of phenolic compoundsThe extraction of phenolic compounds in cherry toma-

toes was performed as described by Slatnar et al. (2012), with slight modifications. Three fruits per individual treatment (in five repetitions) were mashed to a pulp and 10 g were extracted with 13 mL methanol containing 3% (v/v) formic acid in a cooled ultrasonic bath for 1 h. After extraction, the extracts were centrifuged for 7 min at 10,000 rpm. The su-pernatant was filtered through a 0.20 µm polyamide filter Chromafil AO-20/25 (Macherey-Nagel, Düren, Germany), transferred to a vial and analyzed on a Thermo Finnigan Surveyor HPLC (Thermo Scientific, San Jose, CA, USA) with a diode array detector at 280 nm and 350 nm. Spectra of the compounds were recorded between 200 and 600 nm. The column was a Gemini C18 (150 × 4.6 mm, 3 µm; Phenome-nex, Torrance, USA) operated at 25°C. Samples were eluted according to the gradient described by Marks et al. (2007).

All phenolic compounds were identified by an HPLC-Fin-nigan MS detector and an LCQ Deca XP MAX (Thermo Fin-nigan, San Jose, CA, USA) described by Mikulic-Petkovsek et al. (2016). The identification of compounds was confirmed by fragmentation, comparison of retention times and com-pound spectra as well as by adding the standard solution to the sample (Anton et al., 2014).

Statistical analysisStatgraphics Plus 4.0 program (Manugistics Inc., Rock-

ville, Maryland, USA) was used for data analysis. A one-way analysis of variance (ANOVA) and Least Significant Differ-ence (LSD) test (p-values of less than 0.05 were considered statistically significant) were used to detect significant dif-ferences in the content levels of the analysed parameters among different cluster thinning treatments, separately for each cluster part (proximal, middle, distal). A separate anal-ysis of the yield was carried out for each individual harvest date, and the results of the LSD test are shown where statis-tically significant differences occurred. Results of chemical analysis are presented as mean values, expressed in fresh mass (FW), with the corresponding standard errors (SE).

Results and discussionCluster thinning is an effective measure to manipulate

source and sink balance of fruit bearing plants (Heuvelink, 1996; Matsuda et al., 2011) in order to regulate crop yield quality (Li et al., 2015). The results of our study indicate that



the control plants (not subjected to cluster thinning) exhibit the highest yield (42.26 t ha-1; 2.64 kg per plant), followed by tomato plants subjected to 2∕₃ cluster thinning (31.39 t ha-1; 1.96 kg per plant). The lowest yield was detected in ½ cluster thinning treatment (24.22 t ha-1; 1.51 kg per plant) (Figure 1). Li et al. (2015) stressed out that during the full fruiting stage of tomato, removing one half of the fruit load resulted in significantly higher dry mass of the leaves and stems and lower dry mass of the fruits, suggesting a source limitation. In our study, the number of cherry tomato fruits harvested per plant during the season declined significantly in the same or-der as was detected for yield: control (160.8 fruits per plant) > 2∕₃ thinning (96.3 fruits per plant) > ½ thinning (72.1 fruits per plant) (Figure 2). The dynamics of fruit yield per plants,

expressed in fruit mass and in the number of fruits per plant, showed evident thinning treatments’ related pattern (Figure 1). During the first two weeks of the harvest period, between 98 and 115 days after transplanting (DAT), a delay in fruit maturation was observed in control plants. This caused a lower fruit yield per plant in comparison to the plants from the thinning treatments. After this period, yield of the control plants increased dramatically, as in the short harvesting peri-od (from 105 to 115 DAT), fruits on unthinned cluster , from the 1st and the 2nd cluster position were harvested (Figure 3). Plants from the control treatment were characterized by higher yield in comparison to the yield of the thinning treat-ment plants throughout the end of the growing period, which resulted in higher total yield of control plants.

12

FIGURE 2. Effect of cluster thinning treatments of cherry tomato on cumulative fruit yield (g plant-1) (A) and the number of fruit per plant. Means ± standard error (n=4) are reported. Different letters above symbols indicate statistically significant differences among treatments (p <0.05; LSD tests) at each sampling.

NSNS

a aa

a aa

cc c c c c

NSNS

NS

NS NS

bb b b b b

0

500

1000

1500

2000

2500

3000

95 105 115 125 135 145 155 165

Mea

n fru

it yi

eld

(g p

lant

-1)

Days after transplantingControl 1/2 thining 2/3 thining

A

NS NSNS

NSNS

a aa

aa

a

b b b b b b

NS NSab

ab bb b b

020406080

100120140160180200

95 105 115 125 135 145 155 165

Num

ber o

f fru

it pl

ant-1

Days after transplantingControl 1/2 thining 2/3 thining

B

Figure 2. Effect of cluster thinning treatments of cherry tomato on cumulative fruit yield (g plant-1) (A) and the number of fruit per plant. Means ± standard error (n = 4) are reported. Different letters above symbols indicate statistically significant differences among treatments (p < 0.05; LSD tests) at each sampling.



The fruit position within an individual cluster plays a significant role, indicated in higher potential growth rate of the first six fruits compared to other fruits within a cluster (De Koning, 1994). In our study, the mean fruit mass ranged between 22.60 g and 27.95 g and no significant differences among treatments were detected in fruits from the proximal and middle cluster sections, while both thinning treatments significantly increased average fruit mass of fruits from the distal cluster section in comparison to the control treatment

(Table 1). Li et al. (2015) also observed a 1.4-fold higher av-erage fresh mass of cherry tomato fruits from the thinning treatments (half fruit load) compared to fruits from the plants with standard fruit load, suggesting the fruiting toma-to plants were source-limiting. Fruit mass of ‘Sakura F1’ vari-ety was comparable with data reported for round cherry to-mato by Choi et al. (2014) and Ripoll et al. (2016). A decrease in fruit mass from proximal to distal cluster section was re-corded for fruits from the control treatment, and an increase

13

FIGURE 3. Effects of cluster thinning treatments of cherry tomato on the harvest periods regarding the cluster position. Bars indicate the length of the harvest period based on days after transplanting.

Treatment Clusterposition 95 100 105 110 115 120 125 130 135 140 145 150 155 160 165

Control 1234567

Thinning on 1/2 1234567

Thinning on 2/3 1234567

D a y s a f t e r t r a n s p l a n t i n g

Figure 3. Effects of cluster thinning treatments of cherry tomato on the harvest periods regarding the cluster position. Bars indicate the length of the harvest period based on days after transplanting.

Table 1. Effects of thinning treatments on fruit mass (g) and colour parameters of cherry tomato fruits, harvested in the middle of August, from the proximal, middle and distal cluster sections.

ClusterFruit mass (g) L* C* h°* a*/b*

Section ThinningProximal Control 23.97 ± 1.12* 30.99 ± 0.15 a 29.72 ± 0.59 a 32.63 ± 0.72 1.57 ± 0.03 a

Thinning on ½ 27.53 ± 1.10 30.48 ± 0.16 b 28.85 ± 0.56 a 35.53 ± 0.51 1.42 ± 0.02 bThinning on ⅔ 23.66 ± 1.43 31.00 ± 0.15 a 27.12 ± 0.50 b 39.36 ± 0.59 1.24 ± 0.03 c

Middle Control 23.94 ± 0.73 31.61 ± 0.15 27.51 ± 0.39 38.99 ± 0.56 1.25 ± 0.02Thinning on ½ 25.09 ± 1.06 31.51 ± 0.14 28.38 ± 0.41 38.57 ± 0.55 1.20 ± 0.03Thinning on ⅔ 26.47 ± 1.14 31.31 ± 0.17 28.63 ± 0.57 40.34 ± 0.60 1.27 ± 0.02

Distal Control 22.60 ± 0.97 b 31.68 ± 0.19 a 31.18 ± 0.57 35.98 ± 0.77 b 1.43 ± 0.03 aThinning on ½ 27.95 ± 1.01 a 31.83 ± 0.25 a 29.48 ± 0.56 38.35 ± 0.63 a 1.26 ± 0.02 bThinning on ⅔ 26.85 ± 0.72 a 31.10 ± 0.19 b 31.40 ± 0.89 38.41 ± 0.48 a 1.28 ± 0.03 b

Means ± standard error (n=4) are presented.* Different letters (a-c) indicate statistically significant differences among treatments, for individual cluster section (within columns; p<0.05; LSD tests).



in fruit mass for fruits from both thinning treatments (Ta-ble 1). This is partly in accordance with the results of Gautier et al. (2005), who detected 40% decrease of cherry tomato fruit mass from the proximal to distal cluster position and linked the phenomena with earlier flowering of the proximal section. As a result, tomatoes in higher positions began to develop earlier and consequently, accumulated assimilates sooner. This agrees well with the suggestion by other au-thors, who indicated that fruit size depends on the availabil-ity of photoassimilates and in turn these are correlated with the number of fruits (Gautier et al., 2005; Mikulic-Petkovsek et al., 2016; Proietti et al., 2006).

Cluster thinning is a popular practice for the larger fruiting tomato cultivars, that can be performed in order to modify the source-sink relation with the aim of increasing plant production as well as the size and individual fruit mass (Shirahige et al., 2009). Hanna (2009) determined, that cluster thinning to three fruits instead to four significantly increased total marketable yield, reduced cull yield, and increased fruit mass. Cockshull and Ho (1995) similarly reported, that 30% fruit removal from the first three clusters resulted in increased fruit mass and reduced cull. In contrast to the reports for standard tomato varieties, cluster thinning of cherry tomatoes in our study resulted in approx. 60% lower yields, depending on the rate of thinning (Figure 1). An additional negative effect of cluster thinning has been recorded in cherry tomato ‘Sakura F1’, i.e., period of no yield, between 115 and 127 DAT and between 142 and 148 DAT (Figure 3). These could probably be assigned to a shortage of assimilates, required for a continuous maturation of cherry tomato fruit. Namely, during the first sixteen days of the harvest period (until 115 DAT), fruits from the control plants were harvested from the first two cluster positions, while fruits from the ½ thinning treatment were harvested from the first three cluster positions. This might influence the lack of assimilates for the ripening of additional levels of tomato clusters, since fruiting tomato plants are known for their source-limiting (Li et al., 2015). The second period of no yield could probably be linked to similar causes. Contrary, control plants were characterized by constant yield during the season, which is mandatory for tomato producers.

Hue angles (h°) of cherry tomatoes ranged from 32.63 (control, upper section) to 40.34 (2∕₃ thinning, middle section). Significantly lower measurements of h° parameter, monitored on fruits from the distal cluster section of the control plants, indicated that the fruits of this cluster section are the reddest amongst the fruits of the same position (Table 1). Significant differences in chroma (C*) have been detected among thinning treatments only for fruits from the proximal cluster section, with more intense color (higher C* value) measured at the surface of fruits from ½ thinning treatment and control plants. (Table 1). Differences between the other treatments were not significant. a*/b* ratio of cherry tomato skin was used as a reference parameter for ripening stage and enabled the comparison of our results with literature data. Cherry tomato fruits were harvested at visually fully ripe stage consistent with a*/b* values in range from 1.20 to 1.57 (Table 1). According to Raffo et al. (2002), this ratio corresponds to two different maturity stages of tomato fruit: light red (dark orange or red skin) and red (fully red skin). Fruits from distal and proximal sections of the control clusters were characterized by higher a*/b* ratios and were redder than fruits on the same positions on clusters subjected to thinning, which might indicate faster maturation of fruits from control clusters, due to smaller

fruit (Table 1) compared to the fruits from both thinning treatments. Significant differences in lightness (L*) have been detected among cluster thinning treatments in the proximal and distal cluster sections (Table 1).

Primary and secondary metabolitesData for individual sugars, organic acids, ascorbic acid,

lipophilic pigments and polyphenols are presented in Tables 2–5. Cluster thinning affected the individual sugar contents, above all in fruits from proximal and distal cluster sections; however, differences were not always significant (Table 2). Fruits from the proximal and distal sections of thinned clusters were characterized by lower sugar levels compared to the same position on the control plants. Generally, fruit position (proximal, middle, distal) also affected sugar content and a decrease of sugar was detected from proximal to distal parts of the cluster, regardless of the thinning treatment. A comparable pattern has been described for dry matter content in cherry tomato fruits, grown under high competition for assimilates, typical for standard fruit load (un-thinned) cluster (Gautier et al., 2005).

The impact of thinning on the organic acid content was lower than on sugar content; however, significantly higher levels of citric acid have been measured in proximal fruits of the clusters subjected to thinning treatments (Table 2) in comparison to the control plants. These alterations in biochemical traits together with carpometric and color parameters (fruit mass and lower h° and higher C* and a/b values) indicated that cluster thinning might delay fruit maturation, as acid concentration decreases with increasing fruit maturity (Verheul et al., 2015).

In addition to the thinning treatments, fruit acidity also depended on fruit position and followed the opposite pattern compared to sugar composition: distal fruits had the highest citric acid content (3.70, 3.5 and 3.8 mg kg-1 for ½ and 2∕₃ thinning treatments and the control, respectively) followed by the middle and proximal fruits in the cluster.

Ascorbic acid content of cherry tomato fruit was in range from 235 to 285 mg kg-1 FW (Table 2) which is in accord to the reports of several authors (Abushita et al., 1997; Figas et al., 2015; Gautier et al., 2005). Thinning had no significant effect on the content of ascorbic acid in any cluster section.

Sugar/organic acid ratio has been extensively used as a major indicator of tomato acceptability by the consumers since it refers to sweet or sour taste of the produce. High sugar levels and comparatively high organic acid contents are required for ensuring optimal tomato flavour. Low sugar content and high organic acids levels are characteristic for sour-tasting tomato and fruit containing high levels of sugars and low levels of organic acids taste bland. A similarly tasteless flavor has been linked to tomatoes, which accumulate low amounts of sugars and organic acids (Cebolla-Cornejo et al., 2011). Significant differences in sugar/acid ratio have been detected among treatments in the proximal cluster section. Control fruits were characterized by significantly higher sugar/acid ratio compared to fruits subjected to thinning treatments (Table 2), suggesting a sweeter taste of control fruits. Lower sugar/acid ratio, characterized for the proximal fruits of thinned clusters might indicate lower maturity stage of these fruits compared to the fruits from the control treatment, which was confirmed also with lower a*/b* ratio, lower sugar content and higher citric acid content (Tables 1 and 2).

In addition to phenolic-type antioxidants, tomatoes also contain high levels of lycopene and ß-carotene – carotenes



with antioxidative function (Siddiqui et al., 2015). Lycopene is responsible for red and ß-carotene for orange color of tomato fruit and both are accumulated during the differentiation of chlorophyll-containing chloroplasts into carotene-containing chromoplasts (Egea et al., 2010). In all treatments (and cluster sections), lycopene was the major carotenoid component, representing 97% of total carotenoids in cherry tomato fruits, followed by minor amounts of lutein and ß-carotene (Table 3). The average content levels of total carotenoids in tomato fruit ranged between 166.63 and 220.80 mg kg-1 FW, which is somewhat higher than the results of Raffo et al. (2002), who reported a mean level of 127 mg kg1 FW based on analysis of several cherry tomato varieties. No impact of thinning has been recorded on average levels of lycopene, ß-carotene and lutein in the present study (Table 3). Also, no differences in carotenoid levels have been observed between cluster sections. These results did not correspond to the carpometric and chromametric characteristics of

Tab

le 2

. Ef

fect

of c

lust

er th

inni

ng o

n su

gars

(g k

g-1 F

W),

orga

nic

acid

s (g

kg-1

FW

) and

asc

orbi

c ac

id (m

g kg

-1 F

W) c

onte

nts

in c

herr

y to

mat

o fr

uits

, har

vest

ed in

the

mid

dle

of A

ugus

t, fr

om

prox

imal

, mid

dle

and

dist

al c

lust

er s

ecti

on.

Clus

ter se

ction

Trea

tmen

tGl

ucos

eFr

uctos

eSu

crose

Citric

acid

Malic

acid

Asco

rbic

acid

Suga

r/acid

ratio

Prox

imal

Contr

ol38

.29 ±

1.86

*41

.22 ±

1.76

a0.3

5 ± 0.

04a

2.58 ±

0.06

b0.0

9 ± 0.

0228

5.00 ±

19.36

27.06

± 1.

85a

Thinn

ing on

½32

.98 ±

1.87

34.02

± 1.

82b

0.24 ±

0.03

b3.1

6 ± 0.

06a

0.11 ±

0.00

257.5

0 ± 11

.0918

.91 ±

0.86

bTh

inning

on ⅔

32.77

± 1.

5135

.09 ±

1.43

b0.1

8 ± 0.

02b

3.20 ±

0.25

a0.1

1 ± 0.

0227

5.00 ±

12.58

19.18

± 1.

61b

Midd

leCo

ntrol

31.32

± 1.

2234

.46 ±

0.82

0.32 ±

0.08

3.62 ±

0.08

0.16 ±

0.02

235.0

0 ± 12

.5816

.60 ±

0.71

Thinn

ing on

½30

.80 ±

0.22

32.42

± 0.

420.2

3 ± 0.

023.5

6 ± 0.

130.1

2 ± 0.

0127

0.00 ±

12.91

16.03

± 0.

39Th

inning

on ⅔

33.46

± 1.

3435

.57 ±

1.35

0.19 ±

0.01

3.64 ±

0.15

0.15 ±

0.01

257.5

0 ± 8.

5417

.05 ±

0.34

Dista

lCo

ntrol

37.18

± 2.

50a

39.59

± 2.

44a

0.28 ±

0.09

3.81 ±

0.22

0.12 ±

0.01

252.5

0 ± 11

.0918

.53 ±

1.98

Thinn

ing on

½30

.32 ±

0.32

b31

.43 ±

0.56

b0.2

2 ± 0.

013.7

0 ± 0.

220.1

3 ± 0.

0126

5.00 ±

11.90

15.21

± 0.

82Th

inning

on ⅔

32.00

± 0.

78b

33.59

± 0.

70b

0.17 ±

0.01

3.53 ±

0.12

0.13 ±

0.01

257.5

0 ± 12

.5016

.75 ±

0.38

Mean

s ± st

anda

rd er

ror (

n=4)

are p

rese

nted.

* Diffe

rent

letter

s (a-

b) in

dicate

stati

stica

lly si

gnific

ant d

iffere

nces

amon

g tre

atmen

ts, fo

r indiv

idual

cluste

r sec

tion (

withi

n colu

mns;

p<0.0

5; LS

D tes

ts).

Tab

le 3

. Ef

fect

of c

lust

er th

inni

ng o

n ca

rote

noid

s (m

g kg

-1 F

W)

cont

ent i

n ch

erry

tom

ato

frui

ts, h

arve

sted

in th

e m

iddl

e of

Au

gust

, fro

m th

e pr

oxim

al, m

iddl

e an

d di

stal

clu

ster

sec

tion

s.

Clus

ter se

ction

Trea

tmen

tLy

cope

neß-

caro

tene

Lutei

nTo

tal an

alyze

d car

oteno

idsPr

oxim

alCo

ntrol

184.8

6 ± 19

.614.1

8 ± 0.

390.0

3 ± 0.

0118

9.08 ±

19.69

Thinn

ing on

½20

1.64 ±

17.45

4.65 ±

0.30

0.09 ±

0.02

206.1

0 ± 17

.52Th

inning

on ⅔

162.1

5 ± 14

.064.3

6 ± 0.

190.0

7 ± 0.

0516

6.63 ±

14.22

Midd

leCo

ntrol

150.9

2 ± 15

.555.5

9 ± 0.

180.0

3 ± 0.

0215

6.00 ±

15.87

Thinn

ing on

½18

8.50 ±

14.19

4.54 ±

0.30

0.10 ±

0.02

193.1

8 ± 14

.07Th

inning

on ⅔

167.9

1 ± 11

.924.4

6 ± 0.

200.0

6 ± 0.

0317

2.48 ±

12.04

Dista

lCo

ntrol

193.6

2 ± 15

.484.7

0 ± 0.

230.0

1 ± 0.

01b*

198.4

5 ± 15

.45Th

inning

on ½

216.1

2 ± 8.

264.5

3 ± 0.

210.1

0 ± 0.

02a

220.8

0 ± 8.

28Th

inning

on ⅔

174.0

9 ± 9.

494.2

5 ± 0.

240.0

6 ± 0.

03ab

178.5

2 ± 9.

61Me

ans ±

stan

dard

erro

r (n=

4) ar

e pre

sente

d.* D

iffere

nt let

ters (

a-b)

indic

ate st

atisti

cally

sign

ifican

t diffe

renc

es am

ong t

hinnin

g tre

atmen

ts, fo

r indiv

idual

cluste

r sec

tion (

withi

n colu

mns;

p<0.0

5; LS

D tes

ts).



Table 4. Effects of cluster thinning on hydroxycinnamic acids (mg kg-1 FW) in cherry tomato fruits, harvested in the middle of August, from the proximal, middle and distal cluster sections.

Compound Treatment Cluster sectionProximal Middle Distal

Caffeoyl-hexose 1a Control 29.36 ± 0.58* a 25.19 ± 1.32 a 17.14 ± 1.80 bThinning on ½ 17.25 ± 2.80 b 13.50 ± 1.26 b 13.95 ± 2.79 bThinning on ⅔ 27.91 ± 3.17 a 26.00 ± 2.43 a 26.23 ± 3.65 a

Caffeoyl-hexose 2a Control 2.68 ± 0.16 a 2.57 ± 0.27 a 1.91 ± 0.19Thinning on ½ 1.66 ± 0.28 b 1.06 ± 0.07 b 1.08 ± 0.12Thinning on ⅔ 2.26 ± 0.30 ab 1.69 ± 0.25 b 1.56 ± 0.29

Caffeoyl-hexose 3a Control 10.48 ± 0.37 10.26 ± 0.78 8.14 ± 0.72Thinning on ½ 9.21 ± 0.84 8.83 ± 0.73 7.75 ± 0.36Thinning on ⅔ 10.16 ± 0.79 8.35 ± 0.56 8.24 ± 0.71

Dicaffeoylquinic acid 1a Control 0.78 ± 0.05 1.05 ± 0.09 1.15 ± 0.20 abThinning on ½ 0.68 ± 0.08 0.87 ± 0.07 0.75 ± 0.16 bThinning on ⅔ 1.06 ± 0.14 1.11 ± 0.13 1.50 ± 0.11 a

Dicaffeoylquinic acid 2a Control 1.04 ± 0.06 a 0.99 ± 0.11 a 0.74 ± 0.07 aThinning on ½ 0.64 ± 0.11 b 0.41 ± 0.03 b 0.42 ± 0.05 bThinning on ⅔ 0.87 ± 0.11 ab 0.65 ± 0.09 b 0.71 ± 0.06 a

3-caffeoylquinic acida Control 5.36 ± 0.41 b 6.96 ± 0.21 8.44 ± 0.82Thinning on ½ 5.81 ± 0.86 b 10.00 ± 0.93 5.86 ± 1.67Thinning on ⅔ 8.85 ± 0.60 a 9.61 ± 1.11 10.37 ± 1.94

5-caffeoylquinic acida Control 8.66 ± 0.46 a 8.84 ± 0.45 a 9.93 ± 0.16 aThinning on ½ 5.70 ± 0.36 b 5.97 ± 0.50 b 6.37 ± 0.85 bThinning on ⅔ 9.11 ± 0.80 a 8.71 ± 0.84 a 7.93 ± 0.44 b

4-caffeoylquinic acida Control 0.56 ± 0.07 0.46 ± 0.04 0.31 ± 0.05Thinning on ½ 0.64 ± 0.04 0.52 ± 0.06 0.52 ± 0.06Thinning on ⅔ 0.66 ± 0.01 0.54 ± 0.05 0.48 ± 0.06

Tri-caffeoylquinic acida Control 0.10 ± 0.01 0.15 ± 0.02 0.17 ± 0.01Thinning on ½ 0.15 ± 0.02 0.23 ± 0.07 0.22 ± 0.04Thinning on ⅔ 0.12 ± 0.02 0.18 ± 0.04 0.26 ± 0.06

Di-caffeoylquinic acid 1a Control 0.63 ± 0.20 0.78 ± 0.07 a 0.61 ± 0.03 aThinning on ½ 0.50 ± 0.03 0.40 ± 0.04 b 0.44 ± 0.04 bThinning on ⅔ 0.56 ± 0.03 0.61 ± 0.06 a 0.42 ± 0.03 b

Di-caffeoylquinic acid 2a Control 0.12 ± 0.01 0.11 ± 0.01 0.08 ± 0.00 bThinning on ½ 0.10 ± 0.01 0.13 ± 0.01 0.12 ± 0.00 aThinning on ⅔ 0.13 ± 0.01 0.12 ± 0.01 0.10 ± 0.01 b

Coumaroylquinic acidb Control 0.45 ± 0.05 b 0.55 ± 0.06 b 0.74 ± 0.24Thinning on ½ 1.11 ± 0.23 a 1.04 ± 0.15 a 1.13 ± 0.23Thinning on ⅔ 0.48 ± 0.21 b 1.04 ± 0.11 a 0.90 ± 0.02

Coumaric hexoseb Control 0.66 ± 0.02 0.65 ± 0.05 0.51 ± 0.05Thinning on ½ 0.58 ± 0.05 0.56 ± 0.05 0.49 ± 0.02Thinning on ⅔ 0.64 ± 0.05 0.53 ± 0.04 0.52 ± 0.05

Dehydrophaseic acid-hexosea Control 5.09 ± 0.34 4.39 ± 0.38 3.59 ± 0.19Thinning on ½ 4.07 ± 0.29 3.25 ± 0.32 2.75 ± 0.25Thinning on ⅔ 4.75 ± 0.27 3.37 ± 0.28 2.91 ± 0.29

Hydroxycinnamic acids Control 63.01 ± 7.00 63.04 ± 2.66 a 53.58 ± 3.24 aThinning on ½ 51.27 ± 3.21 49.21 ± 5.09 b 41.85 ± 2.11 bThinning on ⅔ 71.32 ± 5.25 65.88 ± 4.40 a 64.00 ± 6.08 a

Means ± standard error (n=4) are presented.* Different letters (a-b) indicate statistically significant differences among thinning treatments, separately for each compound and individual cluster section (within columns; p<0.05; LSD tests).a Compounds are expressed in chlorogenic acid.b Compounds are expressed in p-coumaric acid.



cherry tomato fruits, influenced by cluster thinning and fruit position (proximal, middle and distal) (Table 1). This agrees with many previously reported studies in which total carotenoids and lycopene content in tomato fruits did not correlate with cromaticity values, thus the same a*/b* value can correspond to diverse levels of lycopene (Raffo et al., 2006; Leonardi et al., 2000; Giovanelli et al., 1999). The weak response of carotene compounds to thinning treatments could be linked to the combination of the response to increased irradiance that stimulates carotene synthesis and the response to a treshold temperature that inhibits the carotene synthesis (Rosales et al., 2001; Dumas et al., 2003). On the other hand, Coyago-Cruz et al. (2017) indicated that

individual carotenoid levels exhibited significant differences among diverse fruit positions in the cluster. In this regard, there are reports indicating that the carotenoid content can be altered by changes in the solar radiation (Li et al., 2013). In this study, the lycopene and total carotene content increased from the proximal to distal fruits, within the individual thinning treatment, although the differences were not significant.

Although cherry tomatoes are reportedly a good source of phenolic compounds, the effect of agricultural techniques (such as cluster thinning) on the content of phenolics has not been documented until now. In the present study, 17 individual phenolic compounds from four different

Table 5. Effects of cluster thinning on hydroxybenzoic acids, flavonols and flavanone (mg kg-1 FW) contents in cherry tomato fruits, harvested in the middle of August, from the proximal, middle and distal cluster sections.

Compound TreatmentCluster section

Proximal Middle DistalHomovanillic acid-O-hexoside 1a Control 0.60 ± 0.05 0.48 ± 0.04 0.43 ± 0.03

Thinning on ½ 0.57 ± 0.03 0.49 ± 0.04 0.41 ± 0.02Thinning on ⅔ 0.64 ± 0.06 0.47 ± 0.05 0.43 ± 0.05

Homovanillic acid-O-hexoside 2a Control 0.55 ± 0.02 0.54 ± 0.04 0.46 ± 0.02Thinning on ½ 0.48 ± 0.04 0.46 ± 0.04 0.41 ± 0.02Thinning on ⅔ 0.53 ± 0.04 0.44 ± 0.03 0.46 ± 0.03

Hydroxybenzoic acids Control 1.15 ± 0.06 1.02 ± 0.07 0.91 ± 0.02Thinning on ½ 1.05 ± 0.07 0.96 ± 0.07 0.82 ± 0.03Thinning on ⅔ 1.18 ± 0.09 0.91 ± 0.08 0.93 ± 0.07

Quercetin dihexose-deoxyhexoseb Control 0.17 ± 0.01 a 0.16 ± 0.01 0.19 ± 0.00 aThinning on ½ 0.17 ± 0.01 a 0.17 ± 0.01 0.19 ± 0.01 aThinning on ⅔ 0.14 ± 0.00 b 0.18 ± 0.02 0.16 ± 0.01 b

Quercetin hexose-deoxyhexose-pentoseb Control 2.46 ± 0.19 3.44 ± 0.36 4.02 ± 0.28Thinning on ½ 3.60 ± 0.56 4.08 ± 1.15 5.16 ± 0.95Thinning on ⅔ 2.86 ± 0.58 4.17 ± 0.89 6.04 ± 1.32

Quercetin-3-rutinosideb Control 13.69 ± 2.10 16.39 ± 2.35 20.36 ± 1.86Thinning on ½ 15.29 ± 0.74 22.81 ± 4.26 21.79 ± 2.64Thinning on ⅔ 12.37 ± 2.31 14.85 ± 3.64 15.97 ± 5.34

Kaempferol 3-rutinosidec Control 0.23 ± 0.02 0.22 ± 0.02 0.27 ± 0.03Thinning on ½ 0.26 ± 0.04 0.31 ± 0.02 0.26 ± 0.01Thinning on ⅔ 0.26 ± 0.02 0.22 ± 0.05 0.20 ± 0.04

Flavonols Control 16.58 ± 2.33 20.21 ± 2.73 24.83 ± 2.09Thinning on ½ 19.32 ± 0.84 28.71 ± 5.72 27.41 ± 3.51Thinning on ⅔ 15.66 ± 2.85 15.73 ± 3.63 20.59 ± 6.71

Naringenin dihexosed Control 0.13 ± 0.01 a 0.12 ± 0.01 0.13 ± 0.01Thinning on ½ 0.13 ± 0.01 a 0.13 ± 0.01 0.15 ± 0.00Thinning on ⅔ 0.10 ± 0.00 b 0.14 ± 0.02 0.13 ± 0.01

Naringenin chalcone 3.5. di C hexosed Control 5.99 ± 0.58 5.04 ± 0.45 5.69 ± 0.47Thinning on ½ 5.52 ± 0.44 7.00 ± 0.78 6.25 ± 0.51Thinning on ⅔ 5.29 ± 0.60 4.40 ± 0.76 4.96 ± 0.47

Flavanone Control 6.15 ± 0.60 5.16 ± 0.45 5.82 ± 0.48Thinning on ½ 5.65 ± 0.44 7.12 ± 0.79 6.39 ± 0.51Thinning on ⅔ 5.41 ± 0.61 4.58 ± 0.75 5.10 ± 0.49

Means ± standard error (n=4) are presented.* Different letters (a-c) indicate statistically significant differences among thinning treatments, separately for each compound and individual cluster section (within columns; p<0.05; LSD tests).a Compounds are expressed in chlorogenic acid.b Compounds are expressed in quercetin-3-galactoside.c Compounds are expressed in kaempferol.d Compounds are expressed in naringenin.



phenolic groups have been quantified in cherry tomato. The group of hydroxycinnamic acids represented 67.7% of total analyzed phenolics and fourteen different compounds were identified from this phenolic group: caffeoyl-hexose 1, 2 and 3, di-caffeoylquinic acid 1 and 2,3-caffeoylquinic acid, 5-caffeoylquinic acid, 4-caffeoylquinic acid, tri-caffeoylquinic acid, di-caffeoylquinic acid 1 and 2, coumaroylquinic acid, coumaric hexose, dehydrophaseic acid-hexose. Four compounds have previously been reported in cherry tomatoes by Choi et al. (2014). The main compound was caffeoyl-hexose 1 and its level was reduced in fruit subjected to ½ cluster thinning compared to other treatments (Table 4). Moreover, the content of nine individual hydroxycinnamic acids was significantly affected by different cluster thinning treatments. Significantly higher levels of seven different individual phenolics (caffeoyl-hexose 1, caffeoyl-hexose 2, dicaffeoylquinic acid 1 and 2, 3-caffeoylquinic acid, 5- caffeoylquinic acid, di-caffeoylquinic acid 1) from the group of hydroxycinnamic acids have been determined in control and 2∕₃ thinning treatment compared to ½ thinning (Table 4). The levels of total analyzed hydroxycinnamic acids in fruit from the upper cluster section were comparable among thinning treatments. Contrary, in the middle and lower section of the cluster, reduced levels of total hydroxycinnamic acids have been measured in fruit subjected to ½ thinning in comparison with the control and 2∕₃ cluster thinning treatment (Table 4). This may indicate that severe cluster thinning diminishes the accumulation of hydroxycinnamic acids in cherry tomato fruit.

From the group of hydroxybenzoic acids homovanilic acid-O-hexoside 1 and 2 were detected in cherry tomatoes. These compounds have previously been identified in tomatoes (Vallverdu-Queralt et al., 2011, 2012). Both compounds were quantified in low levels and no significant differences have been determined among thinning treatments or cluster sections (Table 5).

Quercetin-3-rutinoside was the second most abundant phenolic compound following 3-caffeoylquinic acid and ranged between 12.37 and 22.81 mg kg-1 FW. Two additional quercetin compounds (quercetin dihexose-deoxyhexose and quercetin hexose-deoxyhexose-pentose) and kaempferol 3-rutinoside have been identified from the group of flavonols but their levels were 10- to 100-fold lower (Table 5) compared to rutin. No significant differences in total flavonols have been detected among cluster section (Table 5).

Two naringenin derivatives have been quantified in cherry tomato fruit: naringenin dihexose and naringenin chalcone 3,5-di-C hexose combined representing approx. 6.6% total analyzed phenolics. These two compounds have previously been reported in tomato (Slimestad and Verheul, 2009). Significantly lower content of naringenin dihexose has been measured in proximal fruit of the cluster thinned to 2∕₃ cluster length (Table 5).

Moreover, the sum of phenolic content in cherry tomato fruit decreased from the proximal to distal cluster section. This could be linked to the dependence of phenolic compounds on the availability of light and radiation. Additonally, higher content of phenolic compounds in fruit from the proximal cluster section might be related to higher levels of primary metabolites in fruit from this position (Coyago-Cruz et al., 2017). It is well known, that the availability of primary metabolites greatly affect the synthesis of secondary metabolites in fruit. Higher fruit number of cherry tomatoes in the distal cluster section suggests altered source-sink relationship in favour of the sink. This consequently leads

to lower levels of primary metabolites as the same quantity of assimilates has to be distributed among all fruit (Mikulic-Petkovsek et al., 2016).

ConclusionThe following practical considerations can be

summarized from the results: cluster thinning influenced 1) a higher fruit yield at the beginning of the harvest period, between 98 to 115 days after transplanting (DAT), after that period, a strong increase in the yield of unthinned plants occurred, which lasted to the end of the harvest period and resulted in higher total fruit yield of control plants; 2) an increase of average fruit mass – an undesirable trait for this cherry tomato cultivar; 3) a discontinuity of the crop yield in ½ thinning treatment, with periods of no yield, between 115 and 127 DAT and 141 and 153 DAT; 4) regardless of the thinning treatment, cherry tomato fruit shows a pattern of decreased sugar levels and increased organic acid levels in proximal and distal fruits, while no changes in carotenoid and phenolic levels could be detected. The exception was the content of hydroxycinnamic acids, which was higher in tomatoes from 2∕₃ thinning treatment and control. However, the mechanism initiated by cherry tomato cluster thinning on the polyphenolic content remains unclear and further studies are necessary.

Under the experimental conditions applied, the influence of cluster thinning on carotenoids and some polyphenols appeared to be insignificant, which could be assigned to the impact of the environmental factors that reportedly influence their levels. It may be concluded that cluster thinning is not a useful measure in cherry tomato production, as these types must be harvested as a whole cluster, in order to obtain continuous crop yield of desirable fruit size and taste. Nevertheless, the findings of health-related compounds in cherry tomato could be used to increase its market value.

AcknowledgmentsThis work is part of the program Horticulture No. P4-

0013-0481, funded by the Slovenian Research Agency (ARRS).

ReferencesAbushita, A.A., Hebshi, E.A., Daood, H.G., and Biacs, P.A. (1997). Determination of antioxidant vitamins in tomatoes. Food Chem. 60, 207–212. https://doi.org/10.1016/S0308-8146(96)00321-4.

Anton, D., Matt, D., Pedastsaar, P., Bender, I., Kazimierczak, R., Roasto, M., Kaart, T., Luik, A., and Pussa, T. (2014). Three-year comparative study of polyphenol contents and antioxidant capacities in fruits of tomato (Lycopersicon esculentum Mill.) cultivars grown under organic and conventional conditions. J. Agric. Food Chem. 62, 5173–5180. https://doi.org/10.1021/jf500792k.

Cebolla-Cornejo, J., Rosello, S., Valcarcel, M., Serrano, E., Beltran, J., and Nuez, F. (2011). Evaluation of genotype and environment effects on taste and aroma flavor components of Spanish fresh tomato varieties. J. Agric. Food Chem. 59, 2440–2450. https://doi.org/10.1021/jf1045427.

Cheniclet, C., Rong, W.Y., Causse, M., Frangne, N., Bolling, L., Carde, J.P., and Renaudin, J.P. (2005). Cell expansion and endoreduplication show a large genetic variability in pericarp and contribute strongly to tomato fruit growth. Plant Physiol. 139, 1984–1994. https://doi.org/10.1104/pp.105.068767.

Choi, S.H., Kim, D.S., Kozukue, N., Kim, H.J., Nishitani, Y., Mizuno, M., Levin C.E., and Friedman, M. (2014). Protein, free amino acid, phenolic, beta-carotene, and lycopene content, and antioxidative and



cancer cell inhibitory effects of 12 greenhouse-grown commercial cherry tomato varieties. J. Food Compos. Anal. 34, 115–127. https://doi.org/10.1016/j.jfca.2014.03.005.

Cockshull, K.E., and Ho, L.C. (1995). Regulation of tomato fruit size by plant-density and truss thinning. J. Hortic. Sci. 70, 395–407. https://doi.org/10.1080/14620316.1995.11515309.

Cortes-Olmos, C., Leiva-Brondo, M., Rosello, J., Raigon, M.D., and Cebolla-Cornejo, J. (2014). The role of traditional varieties of tomato as sources of functional compounds. J. Sci. Food Agr. 94, 2888–2904. https://doi.org/10.1002/jsfa.6629.

Coyago-Cruz, E., Corell, M., Moriana, A., Hernanz, D., Stinco, C.M., and Melendez-Martinez, A.J. (2017). Effect of the fruit position on the cluster on fruit quality, carotenoids, phenolics and sugars in cherry tomatoes (Solanum lycopersicum L.). Food Res. Int. 100, 804–813. https://doi.org/10.1016/j.foodres.2017.08.002.

Dorais, M., Demers, S., Papadopoulos, A., and Van Ieperen, W. (2010). Greenhouse tomato fruit cuticle cracking. Hortic. Rev. 30, 163–184. https://doi.org/10.1002/9780470650837.ch5.

Dumas, Y., Dadomo, M., Di Lucca, G., and Grolier, P. (2003). Effects of environmental factors and agricultural techniques on antioxidant content of tomatoes. J. Sci. Food and Agric. 83(5), 369–382. https://doi.org/10.1002/jsfa.1370.

Egea, I., Barsan, C., Bian, W.P., Purgatto, E., Latche, A., Chervin, C., Bouzayen, M., and Pech, J.C. (2010). Chromoplast differentiation: Current status and perspectives. Plant Cell Physiol. 51, 1601–1611. https://doi.org/10.1093/pcp/pcq136.

Fernandez-Ruiz, V., Sanchez-Mata, M.C., Camara, M., Torija, M.E., Chaya, C., Galiana-Balaguer, L., Rosello, S., and Nuez, F. (2004). Internal quality characterization of fresh tomato fruits. HortScience 39, 339–345. https://doi.org/10.21273/HORTSCI.39.2.339.

Field, S., and Nichols, M.A. (2004). Control of fruit size in hydroponic greenhouse tomatoes. Acta Hortic. 648, 31–37. https://doi.org/10.17660/ActaHortic.2004.648.4.

Figas, M.R., Prohens, J., Raigon, M.D., Fita, A., Garcia-Martinez, M.D., Casanova, C., Borras, D., Plazas, M., Andujar, I., and Soler, S. (2015). Characterization of composition traits related to organoleptic and functional quality for the differentiation, selection and enhancement of local varieties of tomato from different cultivar groups. Food Chem. 187, 517–524. https://doi.org/10.1016/j.foodchem.2015.04.083.

Gautier, H., Rocci, A., Buret, M., Grasselly, D., and Causse, M. (2005). Fruit load or fruit position alters response to temperature and subsequently cherry tomato quality. J. Sci. Food Agr. 85, 1009–1016. https://doi.org/10.1002/jsfa.2060.

Hanna, H.Y. (2009). Influence of cultivar, growing media, and cluster pruning on greenhouse tomato yield and fruit quality. HortTechnology 19, 395–399. https://doi.org/10.21273/HORTSCI.19.2.395.

Huang, C.H., Peng, F., You, Q.G., Xue, X., Wang, T., and Liao, J. (2016). Growth, yield and fruit quality of cherry tomato irrigated with saline water at different developmental stages. Acta Agr. Scand. B. Soil Plant Sci. 66, 317–324. https://doi.org/10.1080/09064710.2015.1111931.

Kasim, M.U., and Kasim, R. (2015). Postharvest UV-B treatments increased fructose content of tomato (Solanum lycopersicon L. cv. Tayfun F1) harvested at different ripening stages. Food Sci. Technol. 35, 742–749. https://doi.org/10.1590/1678-457X.0008.

Li, T., Heuvelink, E., and Marcelis, L.F. (2015). Quantifying the source-sink balance and carbohydrate content in three tomato cultivars. Front. Plant Sci. 6, 416. https://doi.org/10.3389/fpls.2015.00416.

Li, X., Zhu, S.D., Liu, Y.X., Xue, S.Y., and Li, W.W. (2013). Multivariate statistical analysis of low-light tolerance in tomato (Solanum lycopersicum Mill.) cultivars and their ultrastructural observations. J. Plant Growth Regul. 32, 646–653. https://doi.org/10.1007/s00344-013-9330-z.

Marks, S.C., Mullen, W., and Crozier, A. (2007). Flavonoid and chlorogenic acid profiles of English cider apples. J. Sci. Food Agr. 87, 719–728. https://doi.org/10.1002/jsfa.2778.

McGuire, R.G. (1992). Reporting of objective color measurements. HortScience 27(12), 1254–1255. https://doi.org/10.21273/HORTSCI.27.12.1254.

Mikulic-Petkovsek, M., Koron, D., and Veberic, R. (2016). Quality parameters of currant berries from three different cluster positions. Sci. Hortic. 210, 188–196. https://doi.org/10.1016/j.scienta.2016.07.030.

Orazem, P., Mikulic-Petkovsek, M., Stampar, F., and Hudina, M. (2013). Changes during the last ripening stage in pomological and biochemical parameters of the ‘Redhaven’ peach cultivar grafted on different rootstocks. Sci. Hortic. 160, 326–334. https://doi.org/10.1016/j.scienta.2013.06.016.

Proietti, P., Nasini, L., and Famiani, F. (2006). Effect of different leaf-to-fruit ratios on photosynthesis and fruit growth in olive (Olea europaea L.). Photosynthetica 44, 275–285. https://doi.org/10.1007/s11099-006-0019-4.

Raffo, A., Leonardi, C., Fogliano, V., Ambrosino, P., Salucci, M., Gennaro, L., Bugianesi, R., Giuffrida, F., and Quaglia, G. (2002). Nutritional value of cherry tomatoes (Lycopersicon esculentum cv. Naomi F1) harvested at different ripening stages. J. Agric. Food Chem. 50, 6550–6556. https://doi.org/10.1021/jf020315t.

Resh, H.M. (1995). The nutrient solution. In Hydroponic Food Production, H.M. Resh, ed. (Santa Barbara, California: Woodbridge Press Publishing Company), p. 59–122.

Ripoll, J., Urban, L., Brunel, B., and Bertin, N. (2016). Water deficit effects on tomato quality depend on fruit developmental stage and genotype. J. Plant Physiol. 190, 26–35. https://doi.org/10.1016/j.jplph.2015.10.006.

Rosales, M.A., Ruiz, J.M., Hernandez, J., Soriano, T., Castilla, N., and Romero, L. (2006). Antioxidant content and ascorbate metabolism in cherry tomato exocarp in relation to temperature and solar radiation. J. Sci. Food Agric. 86(10), 1545–1551. https://doi.org/10.1002/jsfa.2546.

Shirahige, F.H., de Melo, P.C.T., Jacomino, A.P., de Melo, A.M.T., Purquerio, L.F.V., and Roquejani, M.S. (2009). Yield and qualitative characterization of fresh market tomato hybrids of Italian and Santa Cruz types. Acta Hortic. 821, 81–87. https://doi.org/10.17660/ActaHortic.2009.821.7.

Siddiqui, M.W., Ayala-Zavala, J.F., and Dhua, R.S. (2015). Genotypic variation in tomatoes affecting processing and antioxidant attributes. Crit. Rev. Food Sci. Nutr. 55, 1819–1835. https://doi.org/10.1080/10408398.2012.710278.

Slatnar, A., Stampar, F., and Veberic, R. (2012). Influence of bicarbonate salts, used against apple scab, on selected primary and secondary metabolites in apple fruit and leaves. Sci. Hortic. 143, 197–204. https://doi.org/10.1016/j.scienta.2012.06.027.

Slimestad, R., and Verheul, M. (2009). Review of flavonoids and other phenolics from fruits of different tomato (Lycopersicon esculentum Mill.) cultivars. J. Sci. Food Agric. 89, 1255–1270. https://doi.org/10.1002/jsfa.3605.

Vallverdu-Queralt, A., Jauregui, O., Di Lecce, G., Andres-Lacueva, C., and Lamuela-Raventos, R.M. (2011). Screening of the polyphenol content of tomato-based products through accurate-mass spectrometry (HPLC-ESI-QTOF). Food Chem. 129, 877–883. https://doi.org/10.1016/j.foodchem.2011.05.038.

Vallverdu-Queralt, A., Jauregui, O., Medina-Remon, A., and Lamuela-Raventos, R.M. (2012). Evaluation of a method to characterize the phenolic profile of organic and conventional tomatoes. J. Agric. Food Chem. 60, 3373–3380. https://doi.org/10.1021/jf204702f.



Verheul, M.J., Slimestad, R., and Tjostheim, I.H. (2015). From producer to consumer: greenhouse tomato quality as affected by variety, maturity stage at harvest, transport conditions, and supermarket storage. J. Agric. Food Chem. 63, 5026–5034. https://doi.org/10.1021/jf505450j.

Zhang, C.X., Tanabe, K., Wang, S.P., Tamura, F., Yoshida, A., and Matsumoto, K. (2006). The impact of cell division and cell enlargement on the evolution of fruit size in Pyrus pyrifolia. Ann. Bot. 98, 537–543. https://doi.org/10.1093/aob/mcl144.

Received: Oct. 30, 2018Accepted: Jan. 26, 2019

Address of authors:Ana Slatnar, Maja Mikulic-Petkovsek, Franci Stampar, Robert Veberic and Nina Kacjan Marsic*Agronomy Department, Chair for Fruit, Wine and Vegetable Growing, Biotechnical Faculty, University of Ljubljana, Jamnikarjeva 101, Ljubljana, Slovenia* Corresponding author; E-mail: [email protected]

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