Introduction

Turkey is one of the most important grape growing countries and has about 4,250,000 ton fresh grape production per year in 460,000 ha vineyard area. Grape utilization ranges of Turkey is highly different that is 52 % table grapes, 38 % raisins and 10 % concentrated grape juice, jam, wine production and local products for local markets (Anonymous 2014).

Table grape production occupies an important place in Turkey’s viticulture and Turkey is also a major exporter country of table grape; in this regard, it comes after Chile, Italy, USA and South Africa and ranks fifth in world table grape production (Anonymous 2012).

Seedlessness of the fruit is a particularly desirable characteristic for consumers in the table grape industry (Varoquaux et al. 2000). However, the small size of seedless grapes originating from that poses problems. In order to overcome these problems in enhancement of seedless grape size, seedless grape growers can be used some viticultural or chemical practices (Reynolds et al. 1992; Abu-Zahra 2010; Dimovska et al. 2011).

Plant growth regulators (PGR) are commonly used to increase berry size and enhance the berry quality in grape growing (Kim and Chung 2000). Among plant growth regulators, gibberellic acid (GA3) has been used to increase berry size of seedless grapes for a long time (Korkutal et al. 2008; Dimovska et al. 2011). On the other hand, there has recently been growing interest in the use of substituted phenylurea compounds such as forchlorfenuron (CPPU; N-[2-chloro-4-pyridinyl]-N1-phenylurea) and thidiazuron [TDZ; N-phenyl-N’-1,2,3-thiadiazol-5-ylurea], with synthetic cytokinin like activity in plant tissues, to promote berry set and development in seedless grapes (Nickel 1985).

Thidiazuron and forchlorfenuron, which are cytokinin-like compounds can be used in the production of some table grape cultivars where they are applied after berry set to increase berry size and firmness. So, the influences of these type compounds on table grape cluster are timing and rate dependent (Smith 2008).

Nowadays, seedless grape cultivars are very popular in all around the world and also Turkey due to excessive consumer demand. For this reason, the large majority of new hybrid genotypes are seedless (Cengiz et al. 2012) and various seedless table grape cultivars such as Sultani Cekirdeksiz, Yuvarlak Cekirdeksiz, Pembe Cekirdeksiz, Tekirdag Cekirdeksiz and ‘Recel Uzümü’ are commonly grown for table grape production.

In table grape growing, large berry size is a highly valued characteristic of table grapes, but seedless table grape cultivars do not generally produce berries of sufficient size to be marked in market of their own country.

Desirable effects, which would be obtained from the using of different plant growth regulators depend on several factors, including of grape cultivars, doses and application time of plant growth regulators (Nampila et al. 2010).

This research was to determine the influences of application doses and times of TDZ on yield components and quality parameters of cv. ‘Recel Uzümü’.

Materials and Methods

Research Area and Plant Materials

This research was conducted in 19 year-old vineyard of cv. ‘Recel Uzümü’ located in Tekirdağ Viticultural Research Institute, Turkey (40°58′22.31″N; 27°28′11.46″E; 34 m a.s. l.) during the 2012 growing season.

‘Recel Uzümü’ used in this study is newly bred stenospermocarpic seedless grape cultivar obtained by Tekirdağ Viticulture Institute in Turkey as a hybrid of ‘Elhamra’ x ‘Perlette’ and it has appealing cluster with medium large blue-black berries. In the study, grapevines were planted 2.5 m × 1.5 m apart, trained to a bilateral guyot trellising system and grafted onto 5BB rootstock.

The vineyard was designed and managed by following local standard viticulture practices without applying a single irrigation throughout its whole growing season.

Climatic Characteristics of Study Area

In terms of study area climate, climate is mild and in order to annual mean temperature, sunshine duration per day, relative humidity and total precipitation were respectively recorded as 15.5 °C, 6.7 h, 83.1 % and 670.8 mm for 2012 year.

TDZ Application Doses and Application Times

In present study, it was utilized from three distinct TDZ doses, consisting 0, 5 and 10 mg/L and these doses were applied on grapevines at three times by foliar spraying. On the other hand, TDZ applications were performed at three different times such as Time 1: beginning of berry setting (E-L number: 27), Time 2: berries pepper corn size (E-L number: 29) and Time 3: berries pea size (E-L number: 31) according to modified E-L system of grapevine notified by Coombe (1995) (Table 1).

TDZ was prepared at three dose levels consisting 0, 5 and 10 mg/L and applied at three times by foliar spraying on grapevines of cv. ‘Recel Uzümü’. For this aim, TDZ doses were applied at three different times including, Time 1: beginning of berry setting (E-L number: 27), Time 2: berries pepper corn size (E-L number: 29) and Time 3: berries pea size (E-L number: 31) according to modified E‑L system of grapevine notified by Coombe (1995) (Table 1).

Table 1 Foliar TDZ application times according to different phenological growth stages in grapevines of cv. ‘Recel Uzümü’
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Yield and Quality Characteristics Assessed in Research

In this study, yield components such as berry length (mm), berry width (mm), berry weight (g), cluster length (cm), cluster width (cm) and cluster weight (g) were found out along with quality components such as total soluble solids content (°Brix), titratable acidity (g/L), juice pH, p-value of juice (µW), total phenolic compounds content (mg/L) and total anthocyanin content (mg/L) were analyzed for cv. ‘Recel Uzümü’.

Berry Harvest and Berry Sampling for Analyses

In 2012 growing season, cv. ‘Recel Uzümü’ grapes were harvested on the date of 12 September 2012. Standard analyses (such as soluble solids content, titratable acidity, juice pH and p-value of juice) and measurements (berry length, berry width, berry weight, cluster length, cluster width and cluster weight) were immediately performed after harvest process. However, detailed laboratory analyses such as total phenolic compounds content and total anthocyanin content were conducted later. For this aim, samples of 250-berry were collected from each replicate and these berries were used to determine standard analyses and measurements. It was utilized from 300-berry samples for analyses of total phenolic compounds content and total anthocyanin content. All berry samples were stored at −25 °C until these detailed analyses and prior to analyses beginning, berry samples were removed from −25 °C, allowed to thaw overnight at 4 °C and then homogenized in laboratory blender for 20 s.

Analyses for Total Phenolic Compounds Content and Total Anthocyanin Content

In laboratory analyses, the total phenolic compounds content was determined according to spectrophotometric method notified by Singleton et al. (1978) and it was also utilized from another spectrophotometric method informed by Di Stefano and Cravero (1991) for determining of total anthocyanin content.

Determination of Electrochemical Characteristics (p-values)

P-value, consisting redox potential (mV), pH, p-value (μW) and resistivity (Ώ) is formulated with an equation informed by Hoffmann (1991). In this research, p-values in samples of berry juice from different applications were calculated according to related equation.

Statistical Analyses

This study was designed using the Randomized Complete Parcel Design applying two factor-factorial with four replications and selected two grapevines from per replication. Analysis of variance (ANOVA) was conducted by means of SPSS statistical software (15.0 for windows) and means were compared by LSD (least significant difference) multiple range test at the level of 5 %.

Results and Discussion

In present study, TDZ was applied at three different times and doses on grapevines of cv. ‘Recel Uzümü’. Application doses of TDZ affected yield and quality components cv. ‘Recel Uzümü’, whereas application times of TDZ did not significantly affect these parameters (Fig. 1, 2, 3, 4, 5 and 6; Table 2).

Table 2 Effect of TDZ application dose, application time and interaction of dose x time on yield components of cv. ‘Recel Uzümü’
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Yield Assessment

Berry size is chief quality factor in international markets and grape growers use some plant growth regulators such as thidiazuron, forchlorfenuron and gibberellic acid for increasing berry size (Zoffoli et al. 2009). In this study, TDZ treatments increased all variables related to berry and cluster size (Table 2).

Berry length was significantly increased by TDZ doses and higher berry length means were obtained in 10 ppm (16.32 mm), 5 ppm (15.84 mm) and 0 ppm (14.85 mm).

Applications of 10 and 5 ppm TDZ resulted in remarkably wider berries (14.84 and 14.38 mm) compared to 0 ppm (13.35 mm) (Table 2).

When the mean values of berry weight were examined in Table 2, it was observed that the highest values were obtained from 10 ppm (2.37 g), 5 ppm (2.23 g) and 0 ppm (1.90 g).

There were obviously effects of the TDZ doses on cluster length characteristics of cv. ‘Recel Uzümü’ (Table 2) and higher doses from 0, 5 to 10 ppm seemed to increase the length of cluster (28.97 cm, 31.68 cm and 32.56 cm).

There were no statistically significant differences in cluster width among the TDZ doses (Table 2). The mean values of cluster width were 16.12 cm (0 ppm), 16.07 cm (5 ppm) and 17.38 cm (10 ppm).

Means of cluster weight are presented in Table 2 and cluster weight was affected by increasing TDZ doses such as 0 ppm (505.22 g), 5 ppm (607.70 g) and 10 ppm (650.93 g).

Quality Assessment

In the course of maturation and ripening process, grapes undergo considerable changes and total soluble solids increases towards to harvest (Kanellis and Roubelakis-Angelakis 1993). In this study, effects of TDZ doses on total soluble solids content were found to be significant and total soluble solids content means ranged among 20.80 °Brix in 10 ppm, 21.64 °Brix in 5 ppm and 23.20 °Brix in 0 ppm (Fig. 1).

Fig. 1
figure 1

Effect of TDZ application dose on total soluble solids content

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The acidity level is very important quality factor in table grape. Consumer acceptance of table grapes is strongly influenced by sweetness to acid balance (Winkler et al. 1974). Significant changes were not observed in titratable acidity of cv. ‘Recel Uzümü’ (Fig. 2). The mean titratable acidity contents were varied according to TDZ doses and were determined as 6.02 g/L (0 ppm), 6.77 g/L (5 ppm) and 6.92 g/L (10 ppm).

Fig. 2
figure 2

Effect of TDZ application dose on titratable acidity

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pH is one of the most considerable factors, which affect quality of grape juice and hence the wine (Boulton 1980; Iland 1987). As shown in Fig. 3, the effects of TDZ doses on juice pH were significant. The highest pH means were 3.36 (0 ppm), 3.42 (5 ppm) and 3.36 (10 ppm).

Fig. 3
figure 3

Effect of TDZ application dose on juice pH

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The quality of table grapes may also be observed using the conventional and recently developing electrochemical methods. In this equation, foods or fruits with lower p-values signify more advantageous for consumers (Heilmann 2000; Kara et al. 2012) Fig. 4. represents p-value of berry juices from different doses of TDZ applied grapevines. P-values were affected by the TDZ applications and means were respectively 134.80 μW, 143.12 μW and 150.50 μW for 0 ppm, 5 ppm and 10 ppm.

Fig. 4
figure 4

Effect of TDZ application dose on p-value of juice

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Grape is considered as a natural source of antioxidants due to its high phenolic and anthocyanin content (Ames et al. 1993). In this research, total phenolic compounds content were different from each other in the applications to the extent of total phenolic compounds (Fig. 5). Lower TDZ doses looked to increase total phenolic compounds content and 0 ppm resulted in the highest mean (3030.52 mg/L) than 5 and 10 ppm (2827.50 and 2717.38 mg/L).

Fig. 5
figure 5

Effect of TDZ application dose on total phenolic compounds content

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Anthocyanin accumulation in berry is genetically controlled (Gagne et al. 2011), but viticultural practices canopy management techniques (Kok 2011; Kok et al. 2013; Kok and Bal 2014), girdling and irrigation (Dokoozlian et al. 1995) also influence the coloring of the skin. In present study, TDZ doses had significantly negative effects on the total anthocyanin content of cv. ‘Recel Uzümü’ (Fig. 6). Therefore, the highest total anthocyanin content was observed in berries which received 0 ppm TDZ (647.86 mg/L) while the lowest means were observed in the 5 ppm (604.46 mg/L) and 10 ppm (580.92 mg/L) of TDZ.

Fig. 6
figure 6

Effect of TDZ application dose on total anthocyanin content

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Conclusion

In seedless grape growing on worldwide scale, it can be commonly utilized from different plant growth regulators such as gibberellic acid, forchlorfenuron and thidiazuron to increase berry size. In this research, berry sensory quality was contrarily affected by TDZ doses in cv. Recel Uzumü, by their effects in berry quality variables as expected. However, research results shown that increasing TDZ doses had most favorable effects in enhancing berry sizes when especially applied at 10 ppm, regardless of TDZ application time.