Introduction
Viticulture has become a highly competitive activity and this evolution changed the grower's production perspective into more focus on quality and quantity, to increase the economic value of the crop. The goal is to achieve the best balance between quality and quantity, using fewer economic resources possible. For that, it is more and more necessary for the growers to be aware of the most recent information and technology and to adapt it to their vineyard reality. Many different applications can be made to increase the yield and quality of grapes. For this purpose, researchers have widely used some plant growth regulators. Ethylene is a naturally produced gaseous plant growth regulator that stimulates fruit senescence (Khan et al., Reference Khan, Trivellini, Fatma, Masood, Francini, Iqbal and Khan2015; Öztürk et al., Reference Öztürk, Öztürk, Demirel and Karakaya2015). It is well known that grapes are of non-climacteric nature, which has limited both ethylene and respiration process. Although ethylene levels appear to be much lower than climacteric fruits, the finding that some non-climacteric fruits such as grapes may have minor changes in ethylene and CO2 formation during ripening has led to a reconsideration of the role of ethylene in non-climacteric fruits (Böttcher et al., Reference Böttcher, Harvey, Boss and Davies2013a, Reference Böttcher, Burbidge, Boss and Davies2013b). Ethylene increase during flowering is associated with increased activity of 1-aminocyclopropane-1-carboxylic acid (ACC) and ACC oxidase (ACO) (Ruperti et al., Reference Ruperti, Bonghi, Rasori, Ramina and Tonutti2001). The ethylene production rate is controlled primarily by regulating ACO and ACC synthase (Rath and Prentice, Reference Rath and Prentice2004). It was determined that ACO activity increased significantly at the beginning of grapevine flowering and continued at a high and stable level until the end of abscission (Ruperti et al., Reference Ruperti, Bonghi, Rasori, Ramina and Tonutti2001; Hilt and Bessis, Reference Hilt and Bessis2003). Ethylene biosynthesis can be inhibited by AVG which is an ethylene biosynthesis blocker that stops the activities of ethylene biosynthesis enzymes like 1-aminocyclopropane-1-carboxylic acid (ACC) synthase in plant tissues (Rath et al., Reference Rath, Wargo and Mills2004). AVG is commonly available in the market in the name of ReTain which is used for pre-harvest for improving physiological disorders such as fruit drop in different fruits, especially temperate fruits (Hussain and Singh, Reference Hussain and Singh2020). In recent years, AVG has been used to increase pre-harvest fruit fall and fruit quality. Pre-harvest applications of AVG inhibit ethylene biosynthesis, affecting maturation, abscission and senescence and also reduce post-harvest quality loss in many crops (Pech et al., Reference Pech, Purgatto, Bouzayen and Latche2012; Küçüker et al., Reference Küçüker, Ozturk, Aksit and Genç2015; Çetinbaş, Reference Çetinbaş2018). It has been reported that the application of AVG is generally effective at a concentration between 50 and 1000 ppm (McFadyen et al., Reference McFadyen, Robertson, Sedgley, Kristiansen and Olesen2012). ACC content in flowers. Senescence-promoting property of ethylene limits flower life during flowering and reduces fruit set (Öztürk et al., Reference Öztürk, Öztürk, Demirel and Karakaya2015). Venburg et al. (Reference Venburg, Hopkins, Retamales, Lopez, Hansen, Clarke, Schröeder and Rath2008) and Racsko (Reference Racsko2012) reported that the application of AVG prevented ethylene production in flowers, as a result, the ageing process in the stigma and seed draft was prolonged and fruit set increased. Sanchez et al. (Reference Sanchez, Curetti and Retamales2011) found that AVG applied to different pear varieties during the flowering period increased the fruit set by 22% compared to the control. Also, Hu et al. (Reference Hu, Fukuda, Ohara, Takahashi and Matsui1999) stated that AVG application before flowering in grapevines reduces ACC content in flowers. Although there are several studies about the effects of AVG treatments on pre-harvest fruit drops, ripening, quality in various species such as apples, pear, peach, strawberry, cherry (Pech et al., Reference Pech, Purgatto, Bouzayen and Latche2012; Çetinbaş and Butar, Reference Çetinbaş and Butar2013; Küçüker et al., Reference Küçüker, Ozturk, Aksit and Genç2015; Çetinbaş, Reference Çetinbaş2018) there is limited number of studies available about the effects of fruit set (Öztürk et al., Reference Öztürk, Öztürk, Demirel and Karakaya2015; Aglar et al., Reference Aglar, Yildiz, Ozkan, Ozturk and Erdem2016). There is no information about the effects of AVG applications on fruit set, quality and colouring of grapes. Therefore, the objective of this research was to determine the effects of pre-harvest AVG applications at different doses at the full bloom stage on yield, quality, and the accumulation of anthocyanin in Alphonse Lavallée grape cultivars during 2 years.
Material and methods
The experiment was performed on a 9-year-old grapevine cv. ‘Alphonse Lavallée’ (Vitis vinifera L.) which was grafted on 41 B rootstocks planted at 2 × 3 m spacing and trained to a bilateral cordon system in the vineyard Gönen, Isparta, Turkey (37°56′N, 30°32′E, 1013 m a.s.l.) during two consecutive years (2018/2019 growing season). All standard cultural practices had been used regularly during the trial. In Fig. 1, the meteorological data including rainfall and temperature are shown. The data were obtained from the Turkish State Meteorology Service. In the study, AVG (ReTain (15% AVG) Valent BioScience Corporation) at different concentrations (0 (control), 250, 500, 750 and 1000 mg/l, assuming a spray volume of 1 L/per vine) was applied to the vines at full bloom stage. AVG concentrations were calculated using the active substance. As a surfactant Tween 20 (0.1%,v/v) was used. Control vines were sprayed with water added Tween 20.
Fig. 1. Colour online. Meteorological data (rainfall (column), temperature (line)) in 2018 and 2019.
Determination of grape yield and quality
At harvest, to measure yield per vine (kg), clusters were weighed and divided by vine number. Total cluster weight per treatment was weighed and divided by cluster number to obtain the average weight of clusters (g). Three clusters from each vine per treatment were selected to evaluate average berry weight. Twenty berries collected from the upper, middle and lower sections of the clusters were weighed (g). The average cluster length and width (cm) and average berry length and width (mm) were measured. Berries were then homogenized in a blender, the juice obtained was filtered, and total soluble solids contents (SSC) were measured with a digital refractometer at 20°C and expressed as Brix°. Titratable acidity (TA) was determined by titration of a 10 mL diluted of juice with 0.1 N NaOH to an 8.1 pH. The results were expressed as g tartaric acid L−1 grape juice. To determine the firmness, the skin was removed with a razor blade exposing the flesh at one side of the equator. Mesocarp puncture resistance measurements, indicators of fruit firmness, were made on the exposed flesh using a 5 mm diameter cylindrical probe.
Determination of berry set
To assess the berry set, a fine mesh bag was enclosed just before flowering to three inflorescences per vine from five vines per treatment, selected at random (Fig. 2(a)). After flowering, bags were removed and the opened caps of the flowers in each bag were counted to estimate the number of flowers per bunch (Fig. 2(b), (c)), a method that has been demonstrated not to influence berry set. Corresponding clusters were gathered to determine the number of berry per bunch on the same day as the harvest (Collins and Dry, Reference Collins and Dry2009).
Fig. 2. Colour online. Determination of berry set; (a) fine mesh bags were enclosed before flowering inflorescences, (b) opened caps of the flowers in each bag, (c) counting caps.
Berry set (%) = (total berry number per bunch/number of flowers per bunch) × 100
Determination of coloration
Colour measurement was performed with a colorimeter. The values of L*, a* and b* were recorded. Berry firmness was measured by a 5 mm diameter probe with a texture analyser. 10 mm penetration depth and 100 mm/s were used. For berry firmness and colour assessments, 10 berries in each replicate for per treatment were selected.
Determination of total anthocyanin content
The pH differential method was used to determine total anthocyanin content (Wrolstad, Reference Wrolstad1976). The absorbance was measured at 520 and 700 nm and expressed as malvidin 3-glucoside equivalents.
Statistical analysis
The collected data were subjected to statistical analysis using a randomized complete block design. Statistical analyses were performed using SSPS v.26. Mean values were compared using Duncan's multiple range test at P ≤ 0.05 level. Variables were presented as mean and standard deviation. Each treatment was designed with three replicates consisting of five vines. A classical principal component analysis (PCA) was performed using all variables and two-dimensional plot of the first two principal components (PCs) was created. PCA was performed using SAS-JMP software version 8.0.
Results
The effects of AVG treatments on quality parameters in ‘Alphonse Lavallée’ are shown in Fig. 3. As seen in Fig. 3 there was a significant interaction between treatment × year for quality parameter. In general, although the applications were statistically in the same group, the highest cluster length and width values were obtained from 250 mg/l AVG concentration in the first year. When the effects of AVG applications on the berry properties in terms of berry length, width and weight were examined, it was determined that the effect of the application changed over the years. However, in general, the berries were larger and heavier in vines without AVG application. Treatments with AVG generally were similar to all the variables related to berry and cluster size compared to control, but the results were more striking in the first year.
Fig. 3. Changes in quality parameters in ‘Alphonse Lavallée’ the after treatment with AVG (aminoethoxyvinylglycine) in 2018 and 2019. Data were mean ± standard deviation. Different letters indicate statistically significant differences among the treatments (P ≤ 0.05).
The results in Fig. 4 show that fruit set and yield were significantly affected by treatment × year interaction. 250 mg/l was found to be the highest fruit set ratio (25.5%) in the first year. As in fruit set, the highest yield was obtained from 250 mg/l AVG concentration, while 500 mg/l AVG concentration was the application where the lowest yield was obtained. With 250 mg/l AVG treatment, yield increased as 20.0 and 52.0% when compared to control and 500 mg/l AVG treatments, respectively.
Fig. 4. Colour online. The effect of AVG (aminoethoxyvinylglycine) treatments on berry set and yield in ‘Alphonse Lavallée’, 2018 and 2019. They were depicted by box and whisker plots. Box and whisker plot representations of berry set and yield. The horizontal middle line in boxes denotes the median value. The whiskers below and above the boxes denote the minimum and maximum value, respectively. Different letters indicate statistically significant differences among the treatments (P ≤ 0.05).
As illustrated in Fig. 5, treatment × year interaction was found to be statistically significant. It can be seen that anthocyanin contents were significant and 750 mg/l AVG treatment caused the highest increase in anthocyanin contents in both years. The anthocyanin contents of Alphonse Lavalleé ranged from 15.48 to 73.87 mg/100 g.
Fig. 5. Changes in anthocyanin contents in ‘Alphonse Lavallée’ the after treatment with AVG (aminoethoxyvinylglycine), 2018 and 2019. Data were mean ± standard deviation. Different letters indicate statistically significant differences among the treatments (P ≤ 0.05).
The results of the colour parameter are listed in Table 1. Treatment × year interaction was found statistically significant for L*, a* and b* colour values. Statistically, the highest L* colour value was obtained from all AVG concentrations including control in the first year, while the highest a* colour value was obtained from 1000 mg/l AVG concentration in the second year. The b* value was found to be the highest in the control application without AVG application.
Table 1. The effect of AVG treatments on the colour parameter (L*, a* and b*) values in ‘Alphonse Lavallée’, 2018 and 2019
Data were mean ± standard deviation. Different letters indicate statistically significant differences among the treatments (P ≤ 0.05).
As shown in Table 2, there was a significant interaction between treatment × year for TA and SSC parameters and it was statistically significant. TA increased at the same level in all other AVG concentrations except 750 mg/l AVG application in the first year. In terms of SSC, all AVG treatments were statistically in the same group, except 1000 mg/l AVG treatments in the second year. Alphonse Lavalleé grape variety showed no AVG treatment or year effect for firmness (Table 2).
Table 2. Changes in titratable acidity (TA), soluble solids content (SSC) and firmness in ‘Alphonse Lavallée’ the after treatment with AVG, 2018 and 2019
Data were mean ± standard devination. Different letters indicate statistically significant differences among the treatments (P ≤ 0.05).
The PCA was performed to determine the relationship between the examined parameters for 2018 and 2019 growing season (Fig. 6). As a result of the analysis, five PCs were obtained regarding all yield and quality characteristics examined in both years. The first five components of the PCA explained 84.4% of the total variation in the first year and explanied 86.4% in the second year. Eigen values of the first five PCs were found between 1.17 and 6.25 in the first year and between 1.05 and 5.61 in the second year (data not shown). The eigenvalue of PCs can be used as a criterion to determine how many PCs should be utilized. PCs with eigenvalue 1.0 are considered as inherently more informative than any single original variable alone (Mohammadi and Prassana, Reference Mohammadi and Prasanna2003). PCA was shown two-dimensional scatter plot in Fig. 6. Accordingly, anthocyanin and SSC correlated with PC2 in the first year and anthocyanin, berry set, L, a and firmness correlated PC2 in the second year.
Fig. 6. Colour online. PCA of quality, yield and colour variables for ‘Alphonse Lavalleé’.
Discussion
The effects of AVG on quality characteristics of non-climacteric fruits are not well known. While there is no study on this subject in grapes, studies conducted on cherries have also determined that AVG applications especially at low doses have a positive effect on quality parameter such as fruit width, fruit length and fruit weight (Çetinbaş and Butar, Reference Çetinbaş and Butar2013). Fruit set and yield per vine were increased by AVG as reported by other fruits (Sanchez et al., Reference Sanchez, Curetti and Retamales2011; Öztürk et al., Reference Öztürk, Öztürk, Demirel and Karakaya2015; Pasa et al., Reference Pasa, Silva, Carra, Brighenti, Souza, Schmitz, Katsurayama and Ciotta2017). Increases in these variables resulting from the application of AVG were concentration dependent in the first year, but in the second year, all AVG concentrations tested increased fruit set and yield the same. Many researchers have used growth regulators such as paclobutrazol, benzyladenine, prohexadione-calcium, auxins and gibberellins, including AVG, to increase fruit set (Vilardell et al., Reference Vilardell, Pages and Asin2008; Sanchez et al., Reference Sanchez, Curetti and Retamales2011; Dreyer, Reference Dreyer2013; Öztürk et al., Reference Öztürk, Öztürk, Demirel and Karakaya2015; Aglar et al., Reference Aglar, Yildiz, Ozkan, Ozturk and Erdem2016). AVG is an ethylene blocker. The senescence-promoting feature of ethylene limits the life of the flower during the flowering period and decrease the fruit set. Venburg et al. (Reference Venburg, Hopkins, Retamales, Lopez, Hansen, Clarke, Schröeder and Rath2008) and Racsko (Reference Racsko2012) reported that with AVG applications, ethylene production in the flower was prevented, as a result, the senescense process in the stigma and ovule was prolonged and the fruit set increased. Ogata et al. (Reference Ogata, Hirota, Shiozaki, Horiuchi, Kawase and Ohashi2002) reported that 200 ppm AVG applied to mandarin at the beginning of bloom was effective in increasing fruit set. As evidenced in previous studies, extending flower life by external application of aminoethoxyvinylglycine, a plant growth regulator that inhibits ethylene biosynthesis, can be a powerful tool to improve the pollination yield and fruit set of fruits in adverse weather conditions.
Application of AVG to fruits generally delays their maturation (Çetinbaş and Butar, Reference Çetinbaş and Butar2013). In this study, at the higher concentrations of AVG, soluble solids were decreased, and titratable acidity was increased. However, it was determined that AVG used in low doses decreased acidity and increased the amount of soluble solids. Similar results were also observed in Çetinbaş and Butar (Reference Çetinbaş and Butar2013) and Öztürk et al. (Reference Öztürk, Öztürk, Demirel and Karakaya2015).
Anthocyanins are the phenolic compounds responsible for the red colour of grape and are of great importance in terms of adding flavour, bitterness and sourness to grape and grape products (Burin et al., Reference Burin, Falcão, Gonzaga, Fett, Rosier and Bordignon-Luiz2010). At the same time, due to their potent antioxidant properties, the potential health benefits of human health of these compounds, caused the importance of these compounds to increase (Babalık et al., Reference Babalık, Demirci, Aşcı and Baydar2020). In the present study, results showed that AVG significantly increased anthocyanin contents in grapes when applied in 750 mg/l concentration. However, in some studies on other fruit species such as sweet cherry, it was determined that AVG applications reduce the anthocyanin content. The researchers have attributed this decrease to the conclusion that AVG applications delayed maturity and thus coloration decreased (Kucuker and Oztürk, Reference Kucuker and Ozturk2015).
Colour is an important feature of the grape consumer and is generally responsible for the acceptability of the fruit. Wrolstad et al. (Reference Wrolstad, Durst and Lee2005) stated that colour changes during ripening are due to the degradation of chlorophyll and the accumulation of anthocyanins in grapes. In this study, although the effect of AVG applications on brightness was not statistically very different, its effect on red colour formation was more pronounced at high concentrations. Similar to our findings, Çetinbaş and Butar (Reference Çetinbaş and Butar2013) found that brightness increased with the AVG applications in sweet cherry. However, Çetinbaş (Reference Çetinbaş2018) found that brightness decreased with the AVG applications in pear. Previous studies showed that the effects of AVG treatment especially on fruit colour varied. Non-climacteric and climacteric fruit may have different ethylene receptors and these receptors may have different regulatory functions (Tian et al., Reference Tian, Prakash, Elgar, Young, Burmeister and Ross2000; McGlasson et al., Reference McGlasson, Rath and Legendre2005).
Conclusion
In this study, as long as it is treated in the appropriate concentration, it was determined that pre-harvest AVG treatments increase the berry set, yield and anthocyanin content compared to control treatment but significant differences in all fruit quality were not observed. The best results were obtained from the 250 mg/l of AVG in terms of berry set and yield and 750 mg/l of AVG in terms of anthocyanin accumulation. However, according to this research results conducted here indicates that sprays containing lower concentrations of AVG may also be effective in increasing yields and berry set. In the field, many different factors (cultivar, tree age, cultural management and environmental conditions) may influence the response. In fact, while similar effects were observed on some fruit varieties, opposite results were obtained in other fruits. Since the effect of AVG can vary depending on the dose, application time and fruit type, and since no detailed studies have been encountered with AVG before in grapes, more detailed studies are needed to better understand these issues.
Financial support
This research received no specific grant from any funding agency, commercial or not-for-profit sectors.
Conflicts of interest
The author declares no conflicts of interest exist.
Ethical standards
Not applicable.
