2022 Volume 91 Issue 2 Pages 169-175
In grapes, the ripening time of bunches on lateral or secondary induced shoots, led by simultaneous treatments of current shoot cutting and flower cluster removal, is typically delayed until the cooler seasons. The aim of this study was to estimate the effects of lateral or secondary induced shoot use in the cultivation of ‘Merlot’ grapevine phenology, including number of bunches and weight, yield, and fruit quality. The timings of flowering, coloration and harvest of lateral and secondary induced shoot grapes were delayed by around one month compared with those of vines grown under standard cultivation, which were used as a control. However, there were substantial differences between treatments in terms of number of bunches and weight, yield, and fruit quality. When lateral shoots grew after the current shoot was cut and the flower clusters were removed, the number of bunches decreased, and yield was significantly reduced. In contrast, when the secondary induced shoot germinated after the current shoot, flower clusters, and growing lateral shoots were removed, a stable number of bunches was observed and there was not a severe decrease in yield. Skin anthocyanin content in both the lateral shoot and secondary induced shoot grape berries was increased compared with control. This effect was comparatively stronger in secondary induced shoot grapes subjected to comparatively lower air temperatures during ripening. The results of this study underscore the importance of discriminating between lateral and secondary induced shoots in the process of shifting grape ripening to a cooler season by removing current shoots and flower clusters.
Grape growth and ripening are markedly affected by cultivation conditions and especially the ambient temperature (Jones and Davis, 2000). Hence, global climate change may dramatically affect grape growth and ripening. The Fifth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC, 2014) predicted that the mean global surface temperature will increase by 2.6–4.8°C by the end of the 21st century. In Japan, an approximate 4.5°C increase in mean annual temperature is expected by the end of the 21st century. The annual numbers of hot days and tropical nights are expected to increase concurrently (Japan Meteorological Agency, <https://www.data.jma.go.jp/cpdinfo/GWP/Vol9/pdf/00.pdf>, Accessed: April 1, 2021). Increases in temperature accelerate grape bud break and flowering (van Leeuwen and Darriet, 2016). Therefore, the timing of ripening coincides with high summer temperatures and results in poor coloration, a rapid decline in malic acid content, an increase in pH, and a lack of aroma (Fraga et al., 2012; van Leeuwen and Darriet, 2016). Wine made from these grapes may lack balance and be of comparatively poor quality (Fraga et al., 2012; Mira de Orduña, 2010; van Leeuwen and Darriet, 2016). For these reasons, several cultivation management approaches are being investigated to mitigate the adverse effects of temperature increase on grape quality (Gutiérrez-Gamboa et al., 2021; Palliotti et al., 2014).
A cultivation method to force vine regrowth that has recently attracted attention is shifting the timing of grape ripening to autumn, when temperatures begin to decrease (Gu et al., 2012; Lavado et al., 2019; Martínez de Toda et al., 2019). This forcing of vine regrowth involves simultaneously cutting the growing current shoot between the second and seventh nodes, removing any flower clusters and lateral shoots that have already started to grow, and trimming all remaining leaves on the current shoot. The practice induces the growth of new shoots (hereafter referred to as secondary induced shoots) from the terminal node of the current cut shoot. Using secondary induced shoots can mitigate the negative effects of elevated temperature, and stabilize berry yield. The forced vine regrowth method has been tested on the ʻCabernet Sauvignonʼ, ʻTempranilloʼ, and ʻMaturana Tintaʼ varieties of Vitis vinifera L. In all cases, ripening was successfully delayed by 1–2 months. There were significant decreases in temperature during ripening. This method increased the berry skin anthocyanin levels and lowered pH (Gu et al., 2012; Lavado et al., 2019; Martínez de Toda et al., 2019). Under usual cultivation, it is rare for flower clusters to form on the lateral shoot (hereafter referred to as lateral shoot), which grows from the growing current shoot and where the bunches also grow. Even when flower clusters grow on the lateral shoot, they are usually small and underdeveloped. Moreover, when the current shoot is cut and the flower clusters are removed, and the already growing lateral shoot is allowed to continue growing, it results in a small number of flower clusters and reduced berry yield (Gu et al., 2012). Conversely, Kishimoto et al. (2017) found that when they cut the current shoot and removed the flower clusters from ʻMuscat Bailey Aʼ (Vitis × labruscana ‘Bailey’ and Vitis vinifera ‘Muscat Hamburg’), numerous flower clusters grew on the lateral shoots emerging from the current shoot and stable berry yield was observed. Using these flower clusters also shifted the grape ripening period to autumn when the temperature was lower. However, it is not known how cutting the current shoot, removing the flower clusters before the growth of lateral shoots, and using the subsequent lateral shoot may affect the number of bunches and fruit quality in V. vinifera. Prior attempts by commercial vineyards to use this cultivation method have often made it difficult to differentiate lateral from secondary induced shoots. In order to put this cultivation method to practical use it is important to be able to show the differences in number of bunches, yield, and fruit quality between these two shoot types.
The present study used ‘Merlot’ as the test variety to investigate the effect of two different treatments on number of bunches, bunch weight, yield, and fruit quality. The treatments used involved either; 1) cutting the growing current shoot and removing the flower clusters before the lateral shoot started growing and then using the lateral shoot that grew subsequently, or 2) cutting the current shoot, flower clusters, and the already growing lateral shoot and then using the secondary induced shoot that grew subsequently.
A 2-year study (2017 and 2018) was conducted on the experimental farm of the Faculty of Life and Environmental Sciences of the University of Yamanashi, Kofu, Yamanashi Prefecture, Japan (latitude, 35° 36' 14" N; longitude, 138° 34' 41" E; elevation, 250 m). Eight-year-old in 2017 Vitis vinifera ‘Merlot’ vines grafted onto 101-14 ‘Millardet et de Grasset’ rootstocks were cultivated by a spur pruning trellising system. The vines were planted in rows 45 m long at 1.0-m within-row spacing × 2.5-m between-row spacing. Each vine was pruned to 7–11 spurs per vine. Within rows, 5 grapevines were tested per treatment in 2017 and 7 grapevines were tested per treatment in 2018. Five of the seven grapevines used for each treatment in 2018 were the same grapevines as in the 2017 test.
Shoot treatmentFor the first shoot treatments on May 12, 2017 and May 6, 2018, the growing current shoots were cut between the 5th and 6th nodes and all flower clusters were removed before the lateral shoots started to grow and at the 8–10 separated leaves growth stage [E-L No: 15–16 (Coombe, 1995)]. The subsequent lateral shoots were allowed to grow (Fig. 1A). For the other shoot treatments on May 27, 2017 and May 29, 2018, the shoots were cut between the 5th and 6th nodes and all flower clusters were removed when the growth stage was 15–20 separated leaves and 50% cap-fall completion (E-L number 23–27). The growing lateral shoots were simultaneously removed. The secondary induced shoots were then allowed to grow (Fig. 1B). When the current shoots were cut, no leaves were removed up to the 5th node. Grapevines grown without cutting the current shoot or removing the flower clusters were cultivated under the usual cultivation management conditions as a control (hereafter, control). The number of shoots on each grapevine per plot was adjusted to around 7–11. The timing of grape flowering (E-L number 23, about 50% cap-fall), coloration (E-L number 35, about 50% berry coloring begins), and harvest timing (E-L number 38, 35–40 days after coloration) were monitored according to the E-L system. Air temperature and rainfall during the growing season were measured with the FS-V Field Server (eLAB experience Co., Ltd., Tokyo, Japan) and an OW34-BP rain gauge (Ota Keiki Seisakusho Co., Ltd., Tokyo, Japan).
Current shoot cutting and flower cluster removal in ‘Merlot’ grapevine. Treatments were performed before lateral shoot growth was initiated. Thereafter, lateral shoot growth was allowed (A). The treatment was performed around flowering time with simultaneous removal of small growing lateral shoots. In this way, secondary induced shoot germination was led (B). Source: Kishimoto, 2019, J. ASEV Jpn., 30 (2), p. 50–51.
Total number of bunches per grapevine was enumerated and mean number of bunches was calculated at harvest. All harvested bunches were weighed and mean bunch weight calculated. Thirty berries were randomly sampled thrice per test plot and weighed. Transverse berry diameters were measured with electronic calipers. Total berry skin anthocyanin content was measured according to the method of Tomana et al. (1979). The randomly sampled berries were hollowed out with a cork borer 7.0 mm in diameter and extracted with 5 mL of 1% (v/v) HCl-methanol in a cool dark place for 24 h. The extracted solutions were diluted tenfold and their absorbances were measured at 520 nm in a spectrophotometer (UV-1800; Shimadzu Corp., Kyoto, Japan). The total anthocyanin content was expressed as mg malvidin-3-glucoside equivalents·cm−2 berry skin.
Analysis of grape composition at harvestThirty berries were randomly sampled thrice per test plot to analyze grape composition at harvest. Juice was prepared by manually pressing whole berries to 60% of the total berry weight. Soluble solids content (Brix) was measured with a refractometer (Pocket PaL-1; Atago Co., Ltd., Tokyo, Japan). Titratable acidity was determined by titrating 10 mL juice with 0.1 N NaOH to a pH 8.2 endpoint with an automatic titrator (COM-1700A; Hiranuma Co., Ltd., Ibaraki, Japan), and expressed as tartaric acid equivalent. An organic analysis system comprising HPLC with ion exclusion and post-column pH-buffered electroconductivity detection (LC-20AD; Shimadzu) was used to quantify the tartaric and malic acid levels in the juice samples. Analyses were conducted according to the manufacturer’s instructions. The two analytical columns in series were the RSpak KC-811 (8.0 mm i.d. × 300 mm; Showa Denko K. K., Tokyo, Japan). The mobile phase was 5 mM aqueous p-toluenesulfonic acid. The pH buffer was 5 mM aqueous p-toluenesulfonic acid containing 0.1 mM EDTA and 20 mM bis-(2-hydroxyethyl)-iminotris-(hydroxymethyl)methane. The column temperature was 40°C and the mobile phase and buffer flow rates were both 0.8 mL·min−1.
StatisticsData are means ± standard deviations. Tukey’s tests were performed using Bell Curve for Excel ver. 2.02 (Social Survey Research Information Co., Ltd., Tokyo, Japan). P < 0.05 indicated statistical significance.
Changes in maximum and minimum air temperature and daily rainfall during the 2017 and 2018 growing seasons are shown in Figure 2. The growing degree days from April 1 to October 31 were calculated from the air temperature of each growing season in 2017 and 2018. The experimental farm was in Region V according to the Winkler Index. There were extremely high temperatures between July and August and heavy rainfall between July and September. The total rainfall was extremely high (> 400 mm) in October 2017.
Maximum and minimum air temperatures and daily rainfall at the experimental site during the 2017 and 2018 growing seasons.
Flowering, coloration, and harvest dates in 2017 and 2018 are shown in Table 1. In both 2017 and 2018, the control vines flowered in late May, colored in late July, and were harvested in early September. Lateral shoot flowering occurred in mid-late June, 27 and 28 days later than control in 2017 and 2018, respectively. Coloration occurred in mid-late August, 25 and 23 days later than control in 2017 and 2018, respectively. Harvesting was performed between late September and early October, 26 and 23 days later than control in 2017 and 2018, respectively. Secondary induced shoot flowering occurred in early July, 38 and 48 days later than control in 2017 and 2018, respectively. Coloration occurred in early September, 36 and 41 days later than control in 2017 and 2018, respectively. Harvesting was performed in early October, 34 and 37 days later than the control in 2017 and 2018, respectively. In all plots, the time from flowering to harvest was around 100 days.
Effects of growth stage date, mean maximum and minimum air temperatures, and total rainfall on berry formation and ripening.
In the control, the mean maximum and minimum temperatures during coloration-harvest in 2017 and 2018 were higher than the corresponding temperatures during flowering-coloration. In contrast, for the lateral and secondary induced shoots, the mean maximum and minimum temperatures during coloration-harvest were lower than the corresponding temperatures during flowering-coloration. The mean maximum and minimum temperatures were 1.8–4.1°C higher for the lateral and secondary induced shoots than control during flowering-coloration and 2.4–7.1°C lower for the lateral and secondary induced shoots than control during coloration-harvest (Table 1). Therefore, the control grapes reached coloration in late July and ripened in August. The latter coincided with the hottest time of the year. However, flowering and coloration of the lateral and secondary induced shoots were shifted and arrived around one month later than the control. In 2017, there was no major difference in rainfall between flowering-coloration and coloration-harvest. Nevertheless, in 2018, two typhoons brought heavy rainfall in September. The elevated precipitation caused the lateral and secondary induced shoot growth to exceed that of the control (Table 1).
Number of bunches, bunch weight, and yield at harvestNumber of bunches per vine at harvest dates in 2017 and 2018 are shown in Table 2. Five vines per plot were used in 2017 while seven vines per plot were used in 2018. The mean number of bunches on the control and secondary induced shoot vines were 12.4 and 12.2, respectively, in 2017, and 14.7 and 15.5, respectively, in 2018. There was no significant difference between vines. However, the mean number of bunches on the lateral shoots were 2.2 in 2017 and 3.8 in 2018. These values were significantly lower than those for the control and secondary induced shoots. Bunch weights at harvest are shown in Table 2. Photographs of the berries in 2018 are shown in Figure 3. The bunch weight of the secondary induced shoot vines was significantly lower than control. The lateral shoot bunch had the lowest weight of all three test plots. Moreover, it was small and underdeveloped. There was no difference in the number of bunches per secondary induced shoot vine compared with control. Nevertheless, the yield per secondary induced shoot vine was only around two thirds that of the control in 2017 and 2018, due to the low bunch weight. Conversely, the lateral shoot vines had a relatively lower number of bunches, which were also smaller in size. Hence, their yield was significantly lower than control (Table 2).
Comparison of number of bunches, bunch weight and yield among shoots in 2017 and 2018.
Grape bunches at time of 2018 harvest. (A) Current shoot bunch; (B) lateral shoot bunch; (C) secondary induced shoot bunch.
Berry fresh weight, diameter, and composition at harvest are shown in Table 3. The lateral and secondary induced shoot berries were smaller than those of the control. In 2018, the secondary induced shoot berries were significantly smaller than the lateral shoot berries. The total anthocyanin concentrations in the skins of the berries on the lateral and secondary induced shoots were significantly higher than control in both years. The secondary induced shoot berry skin anthocyanin content was higher than that of the lateral shoot. In 2017, there were no differences among treatments in terms of berry total soluble solid content. In 2018, however, the secondary induced shoot berries had the highest total soluble solid content. The pH was lowest in the secondary induced shoot berries, but there was no difference between control and lateral shoot berry pH in 2017. The secondary induced shoot berries had the highest titratable acidity and malic acid concentrations in both 2017 and 2018.
Berry size and grape composition at harvest of each shoot type in 2017 and 2018.
In grapes, the current shoot tip is elongated because of apical dominance. However, the lateral buds, posterior to the apical bud, begin to grow as soon as the latter is cut (Kebrom, 2017). The forced cultivation in this study made use of this physiological effect. The present study compared the effects of two different cultivation methods on number of bunches, yield, and fruit quality. In the first method, the current shoot and the flower clusters were removed before the lateral shoot could start growing and the subsequent lateral shoot was used. In the second method, the current shoot, flower clusters, and growing lateral shoot were cut and the subsequent secondary induced shoot was used. The timings of flowering, coloration, and harvesting were delayed by about one month in both the lateral shoots and secondary induced shoots compared with control. Consequently, the mean temperature was comparatively lower between coloration and harvest. For the secondary induced shoot, the current shoot and flower clusters were removed around the time of flowering when the lateral shoot started growing. As a result, secondary induced shoot coloration occurred in September and was even later than the lateral shoot. Once again, the mean temperature during ripening was relatively lower. In Yamanashi Prefecture, where the present study was conducted, relatively high rainfall occurs between early summer and early autumn, therefore vigorous shoot growth from the nodes below the cut tips is observed. Despite high midsummer temperatures, the air cools substantially in autumn. Hence, the temperature during ripening would be considerably reduced. Therefore, this cultivation method was expected to have a strong positive effect on berry yield and quality parameters.
When we compared the control, lateral shoot, and secondary induced shoot in terms of relative number of bunches, bunch weight, and yield per vine, we found that the lateral shoot had a significantly lower number of bunches than the control or secondary induced shoot and its harvested bunches were small and underdeveloped. Therefore, the yield per vine of lateral shoots showed the lowest value among the three test plots. In contrast, there was no significant difference between the secondary induced shoot and control in terms of number of bunches. However, the bunch weight of the secondary induced shoot was around two thirds that of control. Hence, the secondary induced shoot furnished lower berry yield than control. The comparatively smaller berries on the secondary induced shoot accounted for the fact it had a lower bunch weight than the control. The observations recorded here for the secondary induced shoot were consistent with those reported by Gu et al. (2012) and Martínez de Toda et al. (2019). The authors forced grapevine regrowth by removing the current shoot and flower clusters and growing lateral shoots with relatively smaller berries, lower bunch weights, and reduced yield. In general, grape flower bud formation begins with primordium (anlage) differentiation into the current shoot axillary bud. The flower cluster primordium forms from the anlage. During the germination and leafing stages in the year after the dormant period, floral organs (florets) develop on the flower cluster primordium (Srinivasani and Mullins, 1978). In the ‘Merlot’ tested here, the secondary induced shoots that grew after removing the current shoot, flower clusters, and growing lateral shoots formed flower clusters equivalent to those of the control and there was no dormancy period. In contrast, there was little flower cluster induction on the lateral shoots growing after the current shoot and flower clusters were removed. Numerous flower clusters formed on the lateral shoots that grew after removal of the current shoot and flower clusters on ‘Muscat Bailey A’ (Kishimoto et al., 2017). Therefore, flower cluster induction on the lateral shoots may vary with grapevine cultivar. Gu et al. (2012) maximized secondary induced shoot number of bunches and yield when they simultaneously removed all flower clusters, lateral shoots, leaves, and the current shoot. In the present study, however, the number of bunches on the secondary induced shoot led after removal of the current shoot, flower clusters, and lateral shoots (but not the current shoot leaves) was equivalent to control. This suggests that removing the leaves after cutting the primary shoot is not always necessary, depending on the grape cultivation environment. Moreover, a recent study showed cytokinin promotion and abscisic acid inhibition could induce secondary induced shoot development from potential shoots after removing the current shoot, flower clusters, and growing lateral shoots (Pou et al., 2019).
The skins of the berries harvested from lateral and secondary induced shoots had higher total anthocyanin content than the control berries. Anthocyanin accumulation is markedly influenced by temperature during ripening. High temperatures diminish anthocyanin biosynthesis and augment anthocyanin degradation (Mori et al., 2005, 2007; Movahed et al., 2016; Pastore et al., 2017; Yamane et al., 2006). Compared with control, shifting the ripening period lowered the temperature during lateral and secondary induced shoot ripening. This effect may have contributed to the increase in the total anthocyanin content of the berry skins. Elevated total skin anthocyanin content, decreased pulp pH, and increased total pulp and malic acid content were pronounced in the berries on the secondary induced shoots as these fruits were subjected to low temperatures during ripening. These physicochemical changes in the fruit are conducive to winemaking and were consistent with the findings of Gu et al. (2012), Lavado et al. (2019), and Martínez de Toda et al. (2019).
The results of this study highlight the importance of differentiating between lateral shoots and secondary induced shoots of V. vinifera when introducing cultivation methods aimed at shifting the ripening period of grapes to the cooler season of autumn. This is especially important for cultivation methods involving cutting the growing the current shoot and removing flower clusters.
