South African Journal of Enology and Viticulture

Changes in Physicochemical Properties and Enzyme Activities of Four Soils Following the Application of Alkaline Winery Wastewater over Three Simulated Irrigation Seasons

2025-03-10T08:06:24+00:00

The in-field fractional use (augmentation) of undiluted alkaline winery wastewater (WW) with raw water for the irrigation of grapevines can reduce the abstraction of water from natural resources and mitigate global water shortages. However, undiluted WW could pose a threat to soil function and enzyme activities, which are early soil quality indicators. Hence, this study used a pot experiment to compare changes in physicochemical properties and enzyme activities of four different soils irrigated with undiluted WW and municipal water (MW) over three simulated irrigation seasons. The soils were collected from the top 0 cm to 30 cm soil layer to which no WW had previously been applied – in the Stellenbosch (sandy loam and sand), Robertson (clay loam) and Lutzville (sand) regions. The water sources were MW, which served as the control, and undiluted WW, and they were both analysed before each irrigation event. Irrigation with undiluted WW resulted in larger increases in soil pH, electrical conductivity (EC) and exchangeable K and Na for all soils and simulated irrigation seasons. The activities of acid phosphatase, β-glucosidase and urease were negatively affected by the addition of undiluted WW. Changes in acid phosphatase activity were negatively correlated with changes in soil pH and EC, while changes in β-glucosidase activity were negatively correlated with changes in soil pH, EC and exchangeable K, Na and Mg. The pH had a dominant effect because of its influence on enzyme activities, precipitation reactions and the development of salinesodic soils. Root exudates, acidification from nitrogen fertiliser and the uptake of K by crops can mitigate the potential risk of using undiluted alkaline wastewater.

Investigating the Phenolic Composition of Merlot and Shiraz Grape Extracts and Wines Produced from Grapes With Different Seed-to-skin Ratios

2025-03-10T08:06:25+00:00

This study explored how Shiraz and Merlot grape extracts and wines made with different skin-to-seed ratios using various extraction methods differ in terms of phenolic composition. These methods included the Iland, Glories and machine-crushed techniques. Each method varied in extraction solvent, pH, extraction time and grape-processing techniques. The Iland method showed no significant differences between Shiraz and Merlot grapes in terms of anthocyanin concentration and colour density for all treatments. However, tannin concentrations and the total phenolic index varied significantly, with higher tannin levels generally observed in treatments with more seeds. Machine-crushed and microwave extraction did not significantly affect anthocyanin levels in the extracts, but showed differences in tannin concentrations, especially in Merlot grapes. The Glories method showed higher potential anthocyanin levels in the seedless treatments for both cultivars compared to those with seeds. However, the method’s evaluation of seed tannin contribution requires reassessment due to interesting findings in the seedless treatments. In winemaking, treatments with more seeds exhibited the highest anthocyanin and tannin levels, affecting the colour density and total phenolic index over time, especially with extended maceration time. Analysing tannin composition via phloroglucinolysis revealed that seed presence affected tannin molecular weight and composition, with notable differences observed between seedless and seeded treatments in the grape extracts and corresponding wines. Overall, the study underscores the intricate relationship between grape seed ratios, extraction methods and phenolic composition. The findings contribute to understanding how these factors affect wine phenolic composition and could contribute to future research on optimising phenolic extraction in winemaking.

Irrigation of Table Grapes With Refill Lines Set According to Midday Stem Water Potential - Soil Water Content and Seasonal Evapotranspiration

2025-03-10T08:06:25+00:00

Irrigation water is a limited resource in most table grape regions. Furthermore, agriculture competes with urban and industrial needs for water. If climate change reduces rainfall, it could put water resources under even more pressure. Therefore, table grape growers must use their available water efficiently by implementing sound irrigation scheduling practices. In this regard, it is fairly simple to measure midday stem water potential (Ψ_S) and calibrate instruments used for irrigation scheduling against Ψ_S. The objective of the study was therefore to develop guidelines to use this approach for table grape irrigation. The study was carried out in five red and five white commercial table grape vineyards in the Berg River Valley region. For each cultivar there were two plots adjacent to each other. The soil in the experiment plot was allowed to dry out until Ψ_S reached -0.8 MPa. The other plot was irrigated with the rest of the block according to the growers’ schedules. Soil water status and midday Ψ_S were measured concurrently to determine the relationship between grapevine and soil water status for each cultivar. Once irrigation refill points were established, grapevines in the experiment plots were irrigated accordingly for three seasons. The results showed that midday Ψ_S in most of the selected table grape cultivars was well correlated with the soil water content in the root zone. By using this approach to table grape vineyard irrigation scheduling, substantially less irrigation water was applied where grapevines were irrigated according to midday Ψ_S compared to the grower’s irrigation schedules.

Dynamic Interplay: Seasonal Variation and Growth Stage- Dependent Nutrient Dynamics in Grapevine Physiology and Their Implications for Fruit Quality and Yield Optimisation

2025-05-14T06:52:23+00:00

This study investigated the variation in nutrient content in grape petioles and berries throughout the
growing season. Seasonal variation and stage-wise changes in grape fruit yield and quality were correlated
with a corresponding nutrient concentration in the plants and berries. The results show that, among
medium vines, Perlette exhibited lower plant and fruit characteristics than Anab-e-Shahi. Among the
growth stages, the highest was noticed in D9 and the lowest in D1. The study of grapevine development and
nutrient dynamics provides a comprehensive understanding of the intricate relationship between vegetative
growth and fruit development, offering crucial insights into factors that significantly affect grape quality
and yield. The analysis of key parameters such as shoot length, trunk girth, and fruit dimensions, along
with the dynamics of fruit weight and number, emphasises the importance of early-season growth and its
overarching influence on overall vine productivity. Varietal distinctions, notably between Anab-e-Shahi
and Perlette, manifest in unique growth patterns and fruit characteristics. In addition, the investigation
delves into the temporal progression of sugar content, identifying a pivotal phase marked by rapid
escalation followed by a subsequent decline. The study extends its scope to nutrient dynamics, exemplified
by alterations in nitrogen, phosphorus and potassium concentrations in leaf petioles, further enriching
the holistic comprehension of grapevine physiology. The cumulative findings offer valuable insights for
vineyard management practices aiming to optimise grape quality and yield.

Stionic Influence of Grape Cultivar Syrah (Vitis vinifera L.) on Inter-specific Hybrid Rootstocks

2025-05-14T07:19:01+00:00

Rootstocks play a crucial role in commercial viticulture by mitigating abiotic and biotic stresses and enhancing
scion characteristics. Although Dogridge (Vitis champinii) is widely used for wine grapes, it is
generally unsuitable due to its tendency to accumulate higher potassium, phenols, and tannins, along with
lower acidity in berries. In this study, wine grape cultivar Syrah was evaluated on seven interspecific Vitis
rootstocks, namely SO4, 110R, P1103, 140Ru, Fercal, 3309 C and 41B, to assess their influence on the vegetative,
physiological, biochemical and quality traits. The experiment was conducted in a randomised block
design and the data obtained were analysed using SAS software. The experiment revealed significant variations
among rootstocks. Rootstock P1103 showed the earliest berry ripening, longer bunches (14.17 cm),
highest total phenols (158.43 mg 100 ml-1 GAE), total flavonoids (83.5 mg 100 ml-1 QE), and yield (9.26 kg
vine-1). Rootstock 110R induced the earliest budburst and produced longest internodes (10.08 cm), highest
berry TSS (22.26°Brix), total monomeric anthocyanins (406 mg 100 g-1 FW) and lowest juice acidity
(0.40%) along with dense trichomes- indicators of stress resistance. Rootstock 41B showed superior juice
recovery (72.45%), reducing sugars (14.91%) and leaf iron content (408.93 μg g-1). Rootstock SO4 induced
maximum cane length (131.89 cm), bunch weight (170.53 g), berry weight (1.487 g) and length (12.61 mm),
highest leaf chlorophyll ‘a’, total chlorophyll, and P (0.235%) and Zn content (96.67 μg g-1), along with the
highest peroxidase activity. These findings highlight the significant impact of rootstocks selection on Syrah
performance, emphasizing the need for long-term evaluation to determine their commercial suitability.

Screening of Oenological Yeasts for Volatile Phenol Release in Smoke-exposed Red Wine

2025-05-14T07:25:48+00:00

The frequency of wildfires has increased over the past few years, particularly in winemaking countries.
This is partly because of climate change, thereby elevating the risk of producing smoke-tainted wines. The
off-flavours associated with smoke taint originate from volatile phenols, which are progressively liberated
from their glycosylated precursors during the winemaking process. Current strategies to prevent and/or
mitigate the negative impact of smoke taint in wine production are not fully effective because it is difficult
to remove glycosylated volatile phenols without affecting wine quality. One ill-explored avenue could be to
use wine yeasts with extracellular glycosidase activities in combination with other downstream remediation
processes. For this study, grape juice was obtained from smoke-exposed Pinotage grapes. Thirty yeast
strains were screened for their potential to release volatile phenols. Partial fermentations were conducted
on laboratory scale for 96 h, after which volatile phenols were quantified using GC-MS. A large variation
was observed between yeast strains in their ability to liberate volatile phenols, particularly guaiacol, which
serves as a key indicator of smoke taint in wine. Most strains released guaiacol at levels above its detection
threshold in wine (23 μg/L). Nevertheless, Lachancea thermotolerans IWBT Y940, Starmerella bacillaris
IWBT Y550 and Wickerhamomyces anomalus IWBT Y541 displayed the highest total volatile phenol
release in smoked Pinotage, close to that observed with a commercial glycosylase formulation.

Barriers to the Use of Entomopathogenic Nematodes as Biocontrol Agents: South Africa as a Case Study

2025-05-14T07:29:40+00:00

Pesticides are synonymous with conventional agriculture, however in recent years, synthetic pesticides
have been scrutinised for environmental and human health-related toxicity. Biopesticides are a sustainable
alternative, with biopesticide technology promising to meet the market halfway by means of maintaining
the current agricultural economic structure, using input technologies, but sustainably, to promote
biodiversity and healthy ecosystem functioning. Biopesticides, which have the potential to mitigate the
impact of ecosystem collapse from intense agriculture and climate change, have received heavy investment
for product development. However, multiple barriers to biopesticide commercialisation are preventing
their widespread use in viticulture and other South African agricultural industries. A literature review
has established that the barriers can be simplified into three main categories: regulatory, commercial,
and educational. This review seeks to understand the barriers and why, after many years of research and
development and considerable investment, the South African biopesticide market is still only a fraction
of the size of the synthetic product market. Global research is considered, as the issue is not a solely
South African one, and multiple countries are facing similar barriers to achieving biopesticide commercial
success. Moreover, this review provides the context as to why, after almost 20 years of research and product
development, a locally produced entomopathogenic nematode biopesticide product is still unavailable to
South African growers, despite the high demand for such a product.