Department of Viticulture and Oenology

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Browsing Department of Viticulture and Oenology by browse.metadata.advisor "Avenant, Eunice"

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    Bunch quality and fertility of Vitis vinifera L. cv. Prime as affected by gibberellic acid (GA3) and s-abscisic acid (s-ABA).
    (Stellenbosch : Stellenbosch University, 2022-12) Masikane, Nonkululeko Nosipho; Avenant, Eunice; Avenant, J. H. ; Stellenbosch University. Faculty of Agrisciences. Dept. of Viticulture and Oenology.
    ENGLISH ABSTRACT: Table grapes are one of the most cultivated, economically important fruit crops in the world and is one of the major fruit industries in South Africa. There is an increase competition in the market that leads to an increase production costs for South African table grape industry, to produce quality grapes that meet market requirements nationally and internationally. Market requirements for grapes are consumer driven, and are based on bunch structure, berry size, colour uniformity, flavour, texture, seedlessness and firmness. Plant growth regulators (PGRs) have become an important tool in producing grapes of high export quality, and to meet these market requirements. Gibberellic acid (GA3) is one of the registered plant growth regulators that is used as a chemical thinner in the grapevine, it is has been found to play a role in berry set, thinning and development. The effectiveness of PGRs dependent on cultivar, application time and concentration. This study aimed at establishing the effect of gibberellic acid (GA3) and abscisic acid (s-ABA) for thinning, combined with GA3 for berry sizing (applied at the recommended dosages, using different application volumes obtained with commercial spray equipment), on fertility of a 5-year-old Vitis vinifera cv. Prime block, grafted onto Ramsey rootstock on the farm Newgro at Kanoneiland in the Orange River Region. Four thinning treatments were combined with four berry sizing treatments, resulting in 16 treatment combinations. The thinning treatments comprised of a Control (No thinning); 1 ppm GA3 at 10% set and 3 days later; 1 ppm of GA3 x 5, with the first application at 10% set, followed by four more applications at 3-day intervals; and 1 ppm GA3 plus 400 ppm s-ABA at 10% set, followed by 1 ppm GA3 3 days later. All thinning treatments were applied at a volume of 1000 L.ha-1 with a Nobili 2000 T mist blower spray pump. The berry sizing treatments, applied at 7 to 8 mm and 8 to 10 mm berry diameter, respectively, comprised of a Control (Dipping) and three treatments applied by spraying. The same active ingredient dosage (2 x 20g GA3 ha⁻¹) was used for all treatments, however different application volumes were used for the spraying treatments (90 L ha-1 with an electrostatic spray pump (ESS); 250 L.ha-1 and 500 L.ha- 1 respectively with a Cima A T50S2.15.L11 mist blower spray pump. Bunches of all treatments obtained commercially acceptable bunch lengths (>20 cm) and Extra-Large berry size (> 18 mm in diameter). The control had the most compact bunches, but there was no significant difference between the three chemical thinning treatments, regarding bunch length, bunch compactness, berry size and berry size distribution. Therefore, producers could use any of these three chemical thinning treatments for Prime. There was a tendency that the largest berry size was obtained with the Dipping and ESS berry sizing treatments. Although there were significant differences, the percentage of extra small berries of all sizing treatments was very low (< 1) in both seasons. Potential fertility was assessed through forced budding in a glasshouse and bud dissections. Actual fertility was assessed in the vineyard. None of the thinning or sizing treatments negatively affected fertility. All treatments obtained commercially acceptable levels (> 80%) of bud break (ranging from 92 % to 97%) and fertility (more than one bunch per sprouted bud). Fertility was not affected by the GA3 treatments applied over three consecutive seasons, probably due to the dosage range used (1 to 5 g.ha-1 for thinning and 40 g.ha-1 for berry sizing). When making the final decision of which chemical thinning treatment and which berry sizing application technique to use, the effect on berry size and bunch quality should also be considered. None of the treatments evaluated negatively affected berry size and bunch quality. Any of the application techniques evaluated could be used, if GA3 within the recommended dosage range is used and applied at the recommended phenological stages for Prime. This study also provided data on the efficacy of GA3+ABA as thinning agent for table grapes, to be used to extend the registration of s-ABA on table grapes to include its use as a thinning agent.
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    Effect of post-harvest summer pruning on carbohydrate reserve status, bud break and fertility of Sultanina H5 in the Lower Orange River region.
    (Stellenbosch : Stellenbosch University, 2022-12) Toolo, Keboneilwe Boitumelo; Avenant, Eunice; Avenant, J. H.; Stellenbosch University. Faculty of AgriSciences. Dept. of Viticulture and Oenology.
    ENGLISH ABSTRACT: Carbohydrate reserves produced from photosynthesis are stored in perennial tissues of the grapevine in the form of starch and free-sugar fractions or soluble sugars, mostly sucrose, glucose, and fructose. These reserves are highly affected by viticultural practices altering the source-sink relationship in the grapevine. Post-harvest pruning is a practice widely applied by several table grape producers in South Africa aiming to channel carbohydrate reserve accumulation to the remaining shoots. Due to the high input costs of table grape production, any manipulation, including post-harvest summer pruning, should be applied only if it is scientifically proven to have practical and economic benefits. This study, comprising of two trials, aimed to determine whether post-harvest pruning results in increased carbohydrate reserve status, improved bud break and fertility, as well as to establish a base for quantifying and practically assessing the carbohydrate reserve status of grapevines. The first trial focused on establishing the seasonal dynamics of non-structural carbohydrate (NSC) reserves of Vitis vinifera L. cv. Sultanina H5 in the semi-arid Lower Orange River (LOR) and the Mediterranean Hex River Valley (HRV). Root, trunk, cane and/or shoot tissues were sampled monthly and analysed for NSC. The Anthrone method was used to analyse soluble sugars and starch, while enzymatic analysis was used to quantify specific sugars (sucrose, d-fructose and d- glucose). Starch and sucrose were the most abundant forms of NSC in all tissues in both regions. In both regions, soluble sugars in permanent tissues (roots, trunks, canes) reached their highest concentration during dormancy (June-July). The starch concentration was low in all tissues in winter (July), during grapevine dormancy, whereafter it increased to a peak occurring in August (before bud break). A steep decrease in starch concentration was recorded from dormancy to flowering in both regions, indicating a dependency of the vine on carbohydrate reserves during that period. Accumulation of NSC reserves began after flowering to the post-harvest period, reaching their second peaks in autumn. The overall higher soluble sugars and starch (roots and canes) concentrations in the tissues of the Mediterranean region is ascribed to the earlier accumulation of reserves, lower crop load and a shorter post-harvest period characteristic of this region. A basis was established for sampling grapevine tissues for qualitative assessment of grapevine NSC reserve status, linking sampling time to occurrence of peaks in soluble sugars and starch concentrations. It is recommended that sampling for qualitative assessment of soluble sugars should be done after leaf fall, during dormancy (June-July under the conditions of this study). Starch concentrations should be assessed before bud break (August under the conditions of this study). Based on significant positive correlations between NSC concentrations of different tissue types, tissue types that could be sampled for indication of the overall NSC status of the grapevine were identified. Canes and shoots could be sampled and analysed to indicate the overall NSC reserve status of the vine. These tissues are considered the most practical tissue types to sample for determination of grapevine NSC reserve status. The second trial investigated the effect of post-harvest summer pruning applied in the semi-arid Lower Orange River region on NSC reserve status, bud break and fertility of Sultanina H5 grapevines. Five post-harvest pruning treatments were applied, namely an early 33% and a 66% shoot removal pruning treatment one day after harvest (33_1dAH and 66_1dAH respectively), a late 33% and a 66% shoot removal pruning treatment 45 days after harvest (33_45dAH and 66_45dAH respectively) and a control (Ctr), in which no post-harvest summer pruning was applied. To quantify pruning severity, the number and length of removed shoots, as well as the number of leaves and leaf area removed were determined at the time of the post-harvest summer pruning treatment application. After winter pruning was applied, the removed canes and shoots were measured to calculate the overall shoot length and leaf area removed per vine. The day after pruning treatments were applied, photosynthetically active radiation (PAR), as well as photosynthetic activity and related physiological parameters were measured. Cane and/or shoot, stem and root tissue, were sampled on 4 dates for assessing the effect of pruning treatments on NSC reserve status. Bud break and fertility were assessed through forced bud break and bud dissection for potential bud break and fertility, while actual bud break and fertility were assessed in the vineyard. Post-harvest pruning proved to be beneficial for light penetration, but it did not improve the photosynthetic rate of the leaves. A few significant differences were recorded on the impact of the treatments on TNC. These however, do not show a clear trend. Post-harvest summer pruning did not have a significant effect on final bud break and potential fertility of grapevines in the season following the treatment. Based on this one season’s results, post-harvest pruning did not have overall practical benefits. Repeating the treatments for two more seasons on the same data vines, would indicate whether there is a carry-over effect of the practice on NSC, bud break and fertility. It is recommended that in a further phase of this project, available rapid and accurate methods to quantify carbohydrate reserves should be used and/or evaluated for use in grapevine studies, including Near-Infrared spectroscopy, as well as the starch iodine test (already commercially used in the apple and forestry industries).
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    The influence of gibberellic acid (GA₃) for berry thinning and berry sizing on table grape production, quality and fertility of Prime
    (Stellenbosch : Stellenbosch University, 2016-12) Van der Vyver, L.; Avenant, Eunice; Avenant, J. H.; Strever, A. E.; Stellenbosch University. Faculty of AgriSciences. Dept. of Viticulture and Oenology.
    ENGLISH ABSTRACT: Table grapes are one of the major commercially grown non-climacteric fresh fruit crops worldwide. Over centuries the table grape industry became a niche market with increasing competition on the markets, putting pressure on table grape growers to produce quality grapes that meet market requirements nationally and internationally. To meet market requirements regarding bunch size and compactness, as well as berry size, colour, flavour, texture and firmness, viticultural practices for table grape production include the use of plant growth regulators (PGRs). Higher input costs are invested to meet these requirements. This lead to the critical focus on labour-intensive cultivation practices and whether alternative methods could be found to maintain high levels of fertility, production and quality. The the aim of this study was to identify GA₃ application methods and volumes for thinning and sizing treatments of table grapes without negatively affecting fertility. The study was done in a commercial Prime vineyard, grafted onto Ramsey, in Paarl, Berg River Valley, South Africa. There are limited scientific publications reporting research results on this cultivar, specifically regarding the effect of different GA3 application methods and volumes on production, quality and fertility. Thinning and berry sizing treatments were applied according to commercial concentrations recommended for Prime. In this trial, different GA3 application methods and volumes were evaluated. Two GA3 treatments were applied during two phenological stages. The first application was the thinning treatment which was applied at 80-100% full bloom. The second application was the berry sizing treatment which was applied when the berries where at 7-8 mm diameter. Six treatments were applied: Treatment 1 (NoThin + Dip (Control)), comprised of a no thinning application, followed by the berry sizing treatment applied by dipping. Treatment 2 (Thin + Dip) comprised a conventional thinning spray application, followed by a berry sizing treatment applied by dipping. Treatment 3 (Thin + 250 L/ha), Treatment 4 (Thin + 500 L/ha) and Treatment 5 (Thin + 1000 L/ha) comprised conventional thinning spray application, followed by berry sizing treatments applied by spraying with a mist blower with spray volumes of 250 L/ha, 500 L/ha and 1000 L/ha respectively. Treatment 6 (Thin + ESS) comprised a conventional thinning spray, followed by a berry sizing treatment, applied at 72 L/ha with an electrostatic spray pump (ESS). In both seasons, before the thinning application was applied, 15 inflorescences per data experimental unit were marked according to a phenological stage. In the first season, ten inflorescences per data experimental unit were marked at 80-100% full bloom (FB) and five inflorescences were marked at 10% set (referred to in the table grape indusy as 110% full bloom). In the second season five inflorescences per data experimental unit were marked at 80-100% FB, five inflorescences were marked at 10% set and five inflorescences were marked at 100% set. No manual bunch preparation actions were applied to these marked bunches and no berry sampling were done from them. These clusters were evaluated for bunch structure/compactness at harvest. This method was used to determine the optimum time for application of thinning treatments in terms of bunch structure at harvest. The bud break percentage determined through forced budding in June 2015 and June 2016, as well as through assessment in the vineyard (November 2015) did not differ significantly between treatments and was above 80% for all treatments. Commercially acceptable levels of bud break were obtained in both seasons. The potential and actual fertility decreased over the two seasons. In June 2015 Treatment 1 had a significantly higher potential fertility and Treatment 6 had a significantly lower potential fertility compared to the other treatments. In June 2016, no significant differences were found between treatments, although Treatment 6 again had the lowest potential fertility. It seems that Treatments 3 and 6 with lower application volumes and smaller droplet size are associated with lower fertility, possibly due to more effective coverage obtained on bunches (the target organs for berry sizing treatments), but also on the shoots and buds and that GA3 applied to the buds had a negative effect on potential fertility. This was also reflected by the actual fertility and yield obtained in the November 2015, where Treatment 2 had the lowest yield as compared to Treatments 3 and 6 (only significant for Treatment 3). Regarding manual thinning in both seasons, Treatment 1 required the longest time spent per ha and Treatments 2 and 5 required significantly less time, which can be ascribed to the larger berry size and % normal berries obtained with Treatment 2. No significant difference was found between the different spray applications (volumes). Therefore, the “best” method for application will depend on the effect on return fertility. In both seasons, Treatment 1 required the most hours for manual thinning and consequently had the highest cost, verifying the need for chemical thinning of Prime, to save labour cost. Time and cost of manual thinning of Prime using Treatment 2, can be up to 40% lower than with Treatment 1. Time required and cost for Treatments 2 and 5 ranged from 942 to 2578 hours and R12 595 and R31 992, which were in line with the time and cost required for commercial Prime blocks. Berry juice composition was not negatively affected by any of the treatments. The expected berry development and ripening patterns were found. Although a few significant differences were found regarding post-harvest quality, it did not practically impact the marketability of the grapes. Regarding the bunch structure in the 2014/2015 season, there were few significant differences between treatments. With the thinning application applied at 80-100% FB the number of berries per cm lateral length, as well as the number of normal berries per cm lateral length of Treatment 1 was significantly higher compared to Treatment 2, indicating that the bunches of Treatment 1 were more compact than the bunches of Treatment 2. The 80-100% FB Treatment 1 had a significantly higher number of small berries per cm lateral length compared to the other two treatments which can be linked to the longer time required for manual thinning of this treatment. In both seasons a trend was observed that a lower number of berries per cm lateral length (less compact bunches) was obtained with the thinning application applied at 80-100% FB compared to the later applications. The results of this study contribute to the available published scientific results regarding the effect of GA3 application methods (volumes) on fertility of table grapes. Based on the results after the first two seasons of the trial, the following are recommended regarding identifying GA₃ application methods and volumes for effective thinning and sizing treatments of table grapes without negatively affecting fertility: . Treatment 2 (Chemical thinning with a standard GA3 spray application, followed by a GA3 dipping treatment for berry sizing) had the largest berries, less compact bunches and the highest percentage normal berries. This treatment also required the least time for manual thinning. . Practical implementation of Treatment 2 (Chemical thinning with a standard GA3 spray application, followed by a GA3 dipping treatment for berry sizing) in commercial table grape production requires availability of sufficient labour. This is already practically applied by several producers in the industry in situations where they have practical experience of a decline in fertility after GA3 applications. . Current available results indicate that the lower spray application volumes Treatment 3 (250 L/ha) and Treatment 6 (ESS 72 L/ha) were associated with a decrease in fertility, while with Treatment 4 (500 L/ha) no indication of a negative effect on fertility was found. Therefore, repetition of the trial is needed to verify these results and to investigate whether the 500 L/ha spray application volume could be used instead of the current standard industry practice of using 1000 L/ha for the majority PGRs and other spray applications. Using an application volume of 500 L/ha instead of 1000 L/ha will have several practical and economic benefits, in terms of more hectares being sprayed with a one tank mix, decreasing the water foot print as well as the carbon foot print. . It is recommended to repeat the trial for at least one more season to verify results obtained and test repeatability.
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    Water footprint analysis to improve water use efficiency in table grape (Vitis vinifera L. cv. Crimson seedless) production. A South African case study
    (Stellenbosch : Stellenbosch University, 2018-03) Kangueehi, Grace Nandesora; Strever, A. E.; Avenant, Eunice; Stellenbosch University. Faculty of AgriSciences. Dept. of Viticulture and Oenology.
    ENGLISH ABSTRACT: Water scarcity is a major impediment to agricultural production, warranting economically viable water use strategies globally. The aim of this study was to evaluate the effects of differing cultivation conditions as well as environmental effects on table grapes (Vitis vinifera L. cv. Crimson Seedless) in terms of plant growth, plant physiology, yield water use efficiency (WUEy) and irrigation water use efficiency (WUEirr) in the Hex River Valley of the Western Cape, South Africa. The experiment consisted of four commercial vineyard blocks with the following irrigation system/soil scenarios: (1) drip on sandy clay loam; (2) micro-sprinkler on sandy clay loam; (3) micro-sprinkler on loamy fine sand and (4) drip on sandy clay loam. No treatment was applied in this study, and standard viticulture management practices as recommended for the production of export quality Crimson Seedless table grapes were applied in each block by the specific farm. The blue water footprint along the production chain only was determined for three regions in South Africa (one winter & two summer rainfall areas). Data used for the water footprint analysis were obtained through interviews and questionnaires. FruitLook data were also validated against field measurements. The four selected blocks showed great variability in terms of their soil characteristics and vegetative growth responses. Block D had vigorous growth in both seasons and the highest yield during the 2013/14 season, with the best fruit quality in both seasons. In contrast, Block A had poor vegetative growth, lower yield, as well as poor fruit quality in both seasons. Blocks B and D had higher specific leaf area (SLA). Blocks A and B had a tendency towards thinner leaves, which could have been linked to the lower stem water potential (ΨS) measured in those blocks at the different phenological stages. Higher values of net carbon assimilation rate and stomatal conductance corresponded with larger berry size and higher yield. The two blocks that were irrigated with micro-sprinklers had higher irrigation volumes and evapotranspiration (ET). Furthermore, the two micro-sprinkler irrigated blocks had a tendency towards a higher WUEy in the 2014/15 season, due to the higher ET and yield measured in these blocks. The drip irrigated Block D had a higher WUEirr in both seasons, and also produced grapes of the best quality, which means a certain stress level can be applied even when grapevines are cultivated for table grape production, without forfeiting fruit quality. Thus, using a drip irrigation system and irrigation applications as applied for Block D and under similar conditions to that in this study, could reduce the volume of irrigation water used and contribute to saving water. The regional average blue water footprint (WF) over two seasons was 210.35 m3/ton, 392.19 m3/ton and 272.42 m3/ton for the Western Cape, Lower Orange River region and the Northern Province respectively. The regional average WUEy values for both seasons was 5.04 kg/m3, 3.00 kg/m3 and 3.68 kg/m3 for Western Cape, Lower Orange River and Northern Province regions, respectively. Water footprints provide useful information on the water use of a specific area and strategies to improve WUE can be developed based on this information. This information can aid in decision making as to which crop can be produced sustainably with better economic benefits to the production area. Thus, WF determination can be used as a tool to raise awareness, as well as determine crop efficiency, which can be used in debates and decision making regarding water allocations. FruitLook data validation also showed a potential to be used in irrigation management decisions that could contribute to improved WUE. grapevines in general and table grapes specifically, were desktop studies and did not include actual plant growth and physiological measurements. Additionally, most of the global data available do not make a distinction between the different grape types (table grapes, raisin & wine grapes). The plant based measurements in this study also contributes to the scientific knowledge and understanding of how the grapevine’s water use and performance is affected by different soil types and irrigation systems, through direct plant based measurements during critical phenological stages.