Impaginato 273 Adv. Hort. Sci., 2024 38(3): 273­279 DOI: 10.36253/ahsc­16128 https://oaj.fupress.net/index.php/ahs Pruning date and hydrogen cyanamide effects on growth and yield of grapevine var. Cabernet Sauvignon N. Ghimire (*), P. Sapkota, P. Poudel, R. Sapkota, K.C. Dahal Institute of Agriculture and Animal Science, Tribhuvan University Kathmandu, Nepal. Key words: Budbreaker, budburst, hydrogen cyanamide, pruning, viticulture. Abstract: Harvesting the grapes before the monsoon season is crucial to ensure the quality of berry and bunches. This study aims to identify the optimal win­ dow for pruning and hydrogen cyanamide (HC) application to prepone the berry harvesting. The experiment was conducted in randomized complete block design with five treatments and four replications. Treatments were five differ­ ent pruning dates in 2021: Jan. 17, Jan. 24, Jan. 31, Feb. 7 and Feb. 14, followed by 5% HC application one week after pruning. Annual growth stages of grapevine were recorded by using modified E­L growth stage; reproductive attributes recorded during flowering; and vine yield and berry quality attributes recorded at harvesting. The earlier pruning resulted earlier budburst compared to late pruning. Vines prunefed after Feb. 7 had <50% budburst, while vines pruned before Feb. 7 reached 50% budburst, exhibiting no differences in num­ ber of days needed to achieve it. Jan. 17 pruning had the highest budburst (%) and bud fruitfulness (%), where pruning on Feb. 7 had lower values. Average bunch weight did not differ while berry quality attributes differed between treatments for the same day harvest. The negative responses in late pruned and HC treated vines, potentially attributed to the phytotoxic effect of HC on tender buds near the natural time of dormancy break. The early pruning and subsequent application of HC triggered earlier budburst, and advances flower­ ing and harvesting of berries in grapevine. This research demonstrated a poten­ tial techniques for advancing harvesting time (2­3 weeks) in grapevine. 1. Introduction Grape (Vitis vinifera L.) is a non­climacteric berry fruit of the deciduous woody vines belonging to the family Vitaceae, indigenous to Eurasia (This et al., 2006). Grapes can be consumed in fresh or processed products like juice, wine, vinegar, jelly, jam, grape seed oil, and raisins. Cabernet Sauvignon is a widely cultivated grape variety for wine due to its small berries with a higher concentration of tannin and coloring pigment (Robinson et al., 2012). Grape cultivation in Nepal was started about 70 (*) Corresponding author: ghimirenishes@gmail.com Citation: GHIMIRE N., SAPKOTA P., POUDEL P., SAPKOTA R., DAHAL K.C., 2024 ­ Pruning date and hydrogen cyanamide effects on growth and yield of grape‐ vine var. Cabernet Sauvignon. ­ Adv. Hort. Sci., 38(3): 273­279. ORCID: NG: 0009­0004­9674­7420 PS: 0009­0006­7058­2108 PP: 0000­0002­0855­9103 RS: 0000­0002­7342­1071 KCD: 0000­0001­5147­8037 Copyright: © 2024 Ghimire N., Sapkota P., Poudel P., Sapkota R., Dahal K.C. This is an open access, peer reviewed article published by Firenze University Press (https://www.fupress.com) and distributed, except where otherwisenoted, under the terms of CC BY 4.0 License for content and CC0 1.0 Universal for metadata. Data Availability Statement: All relevant data are within the paper and its Supporting Information files. Competing Interests: The Authors declare no conflict of interest. Received for publication 9 May 2024 Accepted for publication 5 August 2024 AHS Advances in Horticultural Science AHS ­ Firenze University Press ISSN 1592­1573 (on line) ­ 0394­6169 (print) http://doi.org/10.36253/ahsc-16128 http://oaj.fupress.net/index.php/ahs http://orcid.org/0009-0004-9674-7420 http://orcid.org/0009-0006-7058-2108 http://orcid.org/0000-0002-0855-9103 http://orcid.org/0000-0002-7342-1071 http://orcid.org/0000-0001-5147-8037 http://www.fupress.com http://creativecommons.org/licenses/by/4.0/legalcode http://creativecommons.org/publicdomain/zero/1.0/legalcode Adv. Hort. Sci., 2024 38(3): 273­279 274 years ago but there was no significant expansion of viticulture farms (Dahal et al., 2017). Currently, few commercial vineyards are producing mainly wine grapes while table grapes are in small quantities. The estimated production of Nepal was 76 t from 20 ha area with a productivity of 8.5 t ha­1 (Atreya et al., 2015) but the demand of grape has been increasing manifolds in recent years (Acharya et al., 2023). It shows there is a huge demand for grapes along with bottlenecks of Nepalese viticulture. The main chal­ lenge is harvesting time coincides with the rainy sea­ son causing a high risk of fungal diseases and insect infestation during ripening resulting in inferior quality berries and bunch (Shrestha, 1998). Such problems are also common in humid subtropical areas in other region too. Grapevine dormant buds starts the resumption of annual growth cycle after winter in most of the sub­ tropical and temperate climates. Chilling require­ ment and breaking dormancy are crucial affecting temperate fruit trees when grown in tropical climates (Botelho and Müller, 2007). Various chemicals, such as mineral oil (Black, 1936), Dinitro­ortho­cresol (Erez and Sur, 1981), Thiourea (Blommaert, 1965), Garlic extract (Botelho and Müller, 2007), and HC have been used to break dormancy in grapevine. Among these chemicals, HC has great efficiency in bud break­ ing (Nir and Levee, 1993) as well as enhances uniform and rapid bud breaking (McColl, 1986; Halaly et al., 2008). However, the effect of HC depends upon the time and concentration used. Hydrogen cyanamide breaks endo­dormancy by respiratory disturbance, hormonal signaling, and oxidative stress (Liang et al., 2019). This research was purposed to advance the natural budburst period, which might lead to bunch­ es being harvested before monsoon. To harvest the crop before monsoon, breaking of bud dormancy earlier than natural time is required. In the warmer climates, pruning followed by HC are employed to induce budburst. Aiming to prepone natural budburst and to allow the berry harvesting before the heavy rainfall or monsoon. 2. Materials and Methods The experiment was conducted from January 17 to July 04, 2021, at the commercial vineyard (27°44’ N, 85°6’ E) in Dhading, on a south­facing plot with a gentle slope at an altitude of 800 meters above mean sea level. The grapevine cv. Cabernet Sauvignon (6 years old) grafted on 5C rootstock, was selected for the research. Five pruning dates followed by HC application treatments was arranged on a Randomized Complete Block Design with five replica­ tions considering a vine as replication (Table 1). To differentiate treatments, vines within replica­ tion were tied with different colored ribbons. One­ year­old vines were spur­pruned, leaving three basal buds per spur. Ten spurs from each vine were select­ ed and tagged with different colored threads. Buds in spur were marked as 1, 2, and 3 from the basal to distal. Hence, 30 buds were marked per vine. Phenological observations using the modified Eichhorn and Lorenz (E­L) grapevine growth stages scale began on February 16, 2021, and carried out in every four days interval until April 26, 2021. The growth stages, reproductive attributes during flower­ ing, vine yield, and berry quality attributes were recorded at harvest. Development parameters such as budburst, fruitfulness in total buds, and fruitful­ ness in burst buds were calculated using the follow­ ing formulas: Budburst (%) = Number of burst buds/Total buds x 100 Observed fruitfulness (%) = Number of buds with inflorescence(s)/ Total buds x 100 Fruitfulness in burst buds (%) = Number of buds with inflores­ cence(s) / Total burst buds x 100 All bunches of each treatment were harvested on the same day, July 4, 2021 to ensure that the mini­ mum standard quality berries and bunches harvested before the monsoon arrives. Quantitative attributes were measured from randomly selected 10 bunches. The qualitative attributes (Total soluble solid and Total titratable acidity) were assessed by randomly selected 10 berries from each selected bunch (Dahal et al., 2019). Data recorded from the field were Table 1 ­ Description of treatment details and coding of treat­ ment practiced in a commercial vineyard, Dhading, Nepal, 2021 Treatments Pruning date 5% HC application date Treatment code T1 January 17 January 24 J17J24 T2 January 24 January 31 J24J31 T3 January 31 February 07 J31F07 T4 February 07 February 14 F07F14 T5 February 14 February 21 F14F21 Ghimire et al. ‐ Pruning and hydrogen cyanamide effect on grapevines 275 entered, tabulated and analyzed using MS Excel 12 and GENESTAT version 18.1. 3. Results Phenological observations Annual growth stages of grapevine. Considerable variation in average E­L growth stages among differ­ ent treatments were observed throughout the exper­ imental period as shown in Table 2. Lower values were recorded in later treated vines (F07F14 and F14F21) while early treated (J17J24 and J24J31) vines had higher values of E­L stages. At the last date of observation (26th April), the average E­L stage of J17J24 and F07F14 were 19.69±6.27 and 3.21±2.98, respectively. Number of days to budburst. The number of days to first budburst differed significantly between treat­ ments while treatments did not significantly differ in days to 50% budburst (Table 3). Budburst was earlier D= Date on phenological observation was done. D0 = 16th Feb.; D4 = 20th Feb.; D8 = 24th Feb.; D12 =28th Feb.; D16 =4th Mar.; D20 = 8th Mar.; D24 = 12th Mar.; D28 = 16th Mar.; Day32= 20th Mar.; D36 =24th Mar.; D40 = 28th Mar.; D46 = 3rd Apr.; D49 =6th Apr.; D51= 8th Apr.; D55 = 12th Apr.; D59 = 16th Apr.; D65 = 22nd Apr.; D69= 26th Apr.; Values are µ ± SE where µ = Mean stage; LSD = Least Significance Difference; ** highly significant at α =5%; NS = Not significant. Table 2 ­ Average E­L stage of grapevine buds in different dates of pruning and HC application, Dhading, Nepal, 2021 Observation day Average E­L growth stage in treatments Statistical analysis J17J24 J24J31 J31F07 F07F14 F14F21 Grand mean LSD (α =5) D0 1.39±0.38 c 1.07±0.11 b 1.03±0.07 b 1.01±0.04 a 1.01±0.04 a 1.10 0.105 ** D4 1.73±0.52 d 1.33±0.24 c 1.16±0.16 b 1.01±0.04 a 1.01±0.04 a 1.25 0.101 ** D8 2.23±0.8 d 1.71±0.45 c 1.31±0.26 b 1.02±0.06 a 1.01±0.05 a 1.47 0.279 ** D12 3.26±1.17 d 2.39±0.76 c 1.73±0.38 b 1.05±0.10 a 1.03±0.07 a 1.89 0.514 ** D16 4.97±1.69 d 3.76±1.4 c 2.71±0.88 b 1.1±0.18 a 1.09±0.15 a 2.72 0.836 ** D20 6.11±1.92 c 5.08±1.84 c 4.14±1.55 b 1.17±0.33 a 1.17±0.24 a 3.53 1.044 ** D24 7.74±2.34 c 6.57±2.29 bc 5.65±2.11 b 1.27±0.46 a 1.43±0.45 a 4.53 1.392 ** D28 8.7±2.55 c 7.25±2.48 bc 6.08±2.24 b 1.39±0.61 a 1.78±0.73 a 5.07 1.527 ** D32 9.35±2.76 c 8.05±2.73 bc 6.86±2.52 b 1.51±0.77 a 2.14±0.95 a 5.61 1.735 ** D36 10.85±4.75 c 8.9±3.02 b 8.11±2.91 b 1.71±1.04 a 2.85±1.39 a 6.48 1.895 ** D40 11.16±3.26 c 9.93±3.38 bc 8.48±3.02 b 1.91±1.29 a 3.36±1.71 a 6.97 2.161 ** D46 12.43±3.63 c 11.1±3.78 bc 9.69±3.46 b 2.12±1.54 a 4.25±2.27 a 7.92 2.510 ** D49 13.79±4.04 c 11.98±4.13 bc 10.58±3.93 b 2.31±1.8 a 4.87±2.62a 8.13 3.017 ** D51 15.1±4.56 b 12.76±4.53 b 12.57±4.52 b 2.50±2.03 a 5.49±3.02 a 9.70 3.525 ** D55 16.09±5 b 13.82±5.02 b 13.61±5.02 b 2.69±2.28 a 6.21±3.49 a 10.48 3.725 ** D59 16.9±5.28 b 14.72±5.32 b 14.63±5.35 b 2.87±2.5 a 6.97±3.97 a 11.21 4.140 ** D65 18.33±5.74 b 16.26±5.92 b 16.00±5.86 b 3.05±2.75 a 7.83±4.52 a 12.25 5.081 ** D69 19.69±6.27 b 17.65±6.46 b 17.53±6.46 b 3.21±2.98 a 8.62±5.06 a 13.29 5.679 ** Table 3 ­ Effect of pruning date followed by HC application on number of days to 1st and 50% budburst, Dhading, Nepal, 2021 Mean with the same letter(s) within the column do not differ significantly by DMRT at 5%. Values are µ±SE where µ = Mean and SE = Standard error. LSD=Least Significance Difference. CV = Coefficient of variance. NA= Not applicable. Treatments Days to the first budburst Days to 50% budburst J17J24 0.8 ±0.8 a 16.8 ±2.8 J24J31 8.0 ±1.26 ab 17.2 ±0.8 J31F07 10.4 ±1.6 b 19.0±1.03 F07F14 26.4 ±3.7 c NA F14F21 24.8 ±4.08 c NA Grand mean 14.1 17.67 LSD 7.93 NA F­probability <0.001 NA CV% 42.0 19.1 Adv. Hort. Sci., 2024 38(3): 273­279 276 in the early pruned vine as compared to late pruned grapevines. Early pruned (Jan. 17) grapevine burst their first bud in 0.8±0.8 days while late pruned vines (Feb. 7) took 26.4±3.7 days after HC application. Growth and development observations Budburst percentage. The overall budburst was less than 50% for all treatments. Significant differ­ ences between treatments were found in different observation dates after treatment application. Early pruned and HC treated vines (J17J24, J24J31, and J31F07) were not only early in budburst, but they also had higher budburst (%) compared to late pruned and HC treated vines. Late pruned and HC treated vines had lower budburst (%) even around 10% as shown in figure 1. HC application close to nat­ ural budburst time damages the buds and buds did not sprout (<4 E­L growth stage), hence late pruned and HC treated (F07F14 and F14F21) vines did not reach the 50% budburst. Observed fruitfulness in total buds. The overall flowering of all treatments was less than 40%, how­ ever, significant difference was observed between treatments on different dates of observations (Fig. 2). Flowering (%) variation among treatments follows a similar trend to that of budburst percentage as shown in figure 1 and figure 2. Late pruned and HC treated vines had lower flowering (%) and delayed in flowering. Vine took 40­49 days to flower after bud­ burst. Late pruned and HC treated vines started to flower after 49 days while earlier treated vines start­ ed flowering after 40 days. Fig. 3 ­ Effect of different timing of pruning followed by HC appli­ cation on observed fruitfulness. Means are separated with different letter(s) for the respective day of observa­ tion using Duncan’s multiple range test at 5%. Fig. 2 ­ Effect of different timing of pruning followed by HC appli­ cation on observed fruitfulness. Means are separated with different letter(s) for the respective day of observa­ tion using Duncan’s multiple range test at 5%. Fig. 1 ­ Effect of different date of pruning followed by HC appli­ cation on budburst (%). Means are separated with differ­ ent letter(s) for the respective day of observation using Duncan’s multiple range test at 5%. Fruitfulness in burst buds. Flowering percentage in burst bud was insignificant between treatments from the last date of bud observation (Fig. 3). On April 26, the flowering (%) observed in the burst bud was 82.6% with the death of average 10% buds and the remaining bud did not reach the flowering stage. Treatments J17J24, J24J31, J31F07, F07F14, and F14F21 had bud death percentage as 14.28%, 13.41%, 6.98%, 6.25%, and 4% of total burst buds, respectively. Yield attributes. The TSS and TA of berries were significantly different between treatments (Table 4). Early pruned and HC treated vines produced berries with higher TSS and lower TTA. TSS and TTA of J17J24, J24J31, J31F07, and F07F14 were statistically similar to each other while F14F21 had a higher TTA and lower TSS value. The average bunch weight was similar for all treatments (Table 4). Ghimire et al. ‐ Pruning and hydrogen cyanamide effect on grapevines 277 4. Discussion and Conclusions This study showed the growth and phenological stages were significantly influenced by the date of pruning followed by 5% HC application in grapevine cv. Cabernet Sauvignon. Budburst depends on warm or forcing conditions in some cultivars after endo­ dormancy (Keller and Tarara, 2010). The general threshold temperature for shoot development is 10°C. To some extent, the budburst date corresponds to the cumulated temperatures above this threshold (Lebon et al., 2004). Martin and Dunn (2000) found that HC did not significantly affect the times of the onset of budburst, 60% budburst, anthesis or verai­ son, or fruit maturity at harvest, but interacted signif­ icantly with later pruning to delay fruit maturity. Martin and Dunn (2000) reported that six­week dif­ ferences in pruning time resulted in 5 days differ­ ences in budburst time in the cultivar Cabernet Sauvignon in Melbourne, Australia. HC treatment prepone budburst of vine due to increased accumula­ tion of H2O2, soluble sugar/starch ratio, IAA, and cytoplasmic protein­tyrosine kinase concentration with decreased ABA concentration (Liang et al., 2019). Delayed winter pruning postponed 10­11 days for budburst which reported a possible solution to prevent spring freeze damage (Persico et al., 2021). In late pruned and HC treated vine, dramatic decrease in budburst was observed. Low budburst is potentially linked to phytotoxic effects caused by late application of HC. As the natural budburst time approaches, buds are succulent and vulnerable to the toxic effect of HC. George and Nissen (1988), George et al. (1988), and Shulman et al. (1983) also reported the drying out of young shoots due to too early or late application of HC. Early burst bud may dry out as succulent and young shoots have to face the frost. In most fruit trees, the biggest effect of HC reported when applied few weeks before the natural budburst (Pontikis, 1989). While the late application (F14F21) may not have an impact because the chemical resis­ tance reduces quickly after being released from endo­dormancy (Snir, 1988; Klinac et al., 1991). Using two different HC application dates (mid­Dec. and mid­Jan.), Or et al. (1999) reported that there was no discernible difference in the budburst (%). In both dates, the budburst was found to be 50% after four weeks and an additional 20% within the following two weeks. Cabernet Sauvignon has a shorter dura­ tion of budburst to flowering period as compared to Merlot and Cabernet Franc in Bordeaux, France (Leeuwan et al., 2004). Further they reported that the low yield was typically associated with low bud­ burst rates, while HC influence on grapevine yield has been attributed to its impact on budburst. A high level of budburst would result in an increased shoot number and, therefore, a high yield (Or et al., 1999). The phytotoxic effect of HC acting upon naturally burst tender buds has been reported since its early application (Shulman et al., 1983). Lower budburst and flowering in late pruned and HC treated vines result in lower fruitfulness. Bud fruitfulness depends upon climatic variables mainly sunshine and daily maximum temperature between 82°F and 90°F and water availability (Williams, 2000). Unfavorable climatic conditions hasten diseases and insect infestation such as anthracnose, Downy mildew, mealy bugs, thrips, and leaf hoppers that result in burst bud mortality (Somkuwar et al., 2021). Vine productivity is a distinguishing feature of a variety that fluctuates depending on several parame­ ters, such as rootstock, and vine management. The significance of pruning in the grapevine is relatively consistent (Rives, 2000). Martin and Dunn (2000) found that the earlier pruned (7 July) vines matured earlier than the later pruned (17 August) vines, and the mean TSS of the berry was 0.91°B lower for the later pruned vines. Dhakal (2021) found insignificant difference between the average bunch weight of vine pruned at different times followed by HC application Table 4 ­ Effect of pruning date followed by HC application on yield attributes of grapevine, Dhading, Nepal, 2021 Mean with the same letter(s) within the column do not differ significantly by DMRT at 5%. Values are µ±SE where µ = Mean and SE = Standard error. LSD=Least Significance Difference. CV = Coefficient of variance. NA= Not applicable. Treatments Total soluble solid (°B) TTA (g/L tartaric acid) Average bunch weight J17J24 18.96±0.55 b 9.93±0.81 a 69.56±14.31 J24J31 19.26±0.59 b 9.93±0.32 a 62.86±8.81 J31F07 18.84±0.89 b 10.27±0.94 a 70.06±6.98 F07F14 17.98±0.43 b 10.87±0.57 a 74.92±12.04 F14F21 16.08±0.71 a 12.72±0.3 b 70.05±6.70 Grand mean 18.22 10.75 69.5 LSD (5% level) 1,829 1,537 na F­probability 0.013 ** 0.00 ** 0.96 ns CV (%) 7.5 10.7 35.50 278 Adv. Hort. Sci., 2024 38(3): 273­279 in Kirtipur, Nepal. This research demonstrated the advancing bud­ burst date through pruning and HC application ulti­ mately advances the harvesting time. Thus, it can be a potential and viable strategy to address the chal­ lenges of monsoon coinciding with harvesting time in grapevine growing areas. This study demonstrated that shoot pruning during second fortnight of January followed by 5% HC application advances 2­3 weeks in harvesting of grapevine without compromising in minimum acceptable berry quality. Particularly, in the subtropical conditions of Nepal, it is recommend­ ed to apply HC before Feb. 7th to optimize its effects with 5% HC application. Acknowledgements Authors express gratitude to the TU, Directorate of research (CRG grape) for funding this research. Additionally, we are thankful to Mr. Kumar Karki, CEO of Kewalpur Agro Farm located in Thakre­10, Dhading, for all possible arrangement to conduct this trial. 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