South African Journal of Enology and Viticulture

Relative Leaf Expansion Rate as an Indicator of Compensatory Growth of Defoliated Vines (Vitis vinifera L. cv. Prokupac)

D. Cirkovic — 2023-11-23

Defoliation is a common practice in vineyards, with numerous benefits for vine microclimate conditions, and
it can significantly improve the composition of grapes. In addition, early defoliation reduces the active leaf
area, which affects the modifications of the source-sink balance and decreases whole-vine photosynthesis.
The reaction of grapevines to early defoliation is to mitigate the effects through compensatory growth,
resulting in more lateral shoots with a greater number of leaves. In this study, we evaluate the use of nondestructive
and continuous measurements of mean and lateral leaf area on the same shoots for the purpose
of monitoring leaf area development and calculating relative leaf expansion rate (RLER) during active
growth. The results show that the grapevine’s ability to recover its leaf area after defoliation depends
mainly on the time of defoliation. Vines defoliated early had time to compensate for the removed leaves by
producing a greater number of lateral shoots with more leaves, resulting in a larger total leaf area. With
a decrease in shoot growth during vegetation, the recovery ability decreases, and compensatory growth
is therefore not enough to restore the reduced leaf area. Based on the value of RLER, it is shown that, if
defoliation is performed in the period of intensive shoot growth, it retards the emergence of new shoots
and leaves over several days, followed by a period of regrowth. Very slow or no growth of shoots and leaves
occurred with defoliation after the véraison stage.

Effects of Soil Ameliorants Produced from Recycled Glass on the Establishment of Table Grapes

P.A. Myburgh — 2023-11-23

Sandy, gravelly or stony soils with low nutrient supply or plant available water are common in the table
grape growing regions of South Africa. A field study was carried out to determine if an ameliorant recycled
from waste glass could enhance the nutrient and water supply during the establishing phase of table
grapes. Two grades of ameliorant, i.e. fine and coarse, were incorporated into the soil before the grapevines
were planted. No ameliorants were applied to the control. After planting, the grapevines were irrigated
by using 2.1 L/h drippers. To establish whether the ameliorants could compensate if less water is applied,
the same treatments were applied under 1.2 L/h drippers. In general, the grapevines responded positively
to the higher irrigation volumes, irrespective of ameliorant application. Where higher irrigation volumes
were applied, the ameliorants did not have any positive effect on soil chemical or grapevine nutrient
status compared to the control. This showed that the ameliorants were chemically inert under the given
conditions. The ameliorants also did not improve grapevine water status, vegetative growth, yield or juice
characteristics. Likewise, the ameliorants could not compensate for any measured aspect of grapevine
performance where less irrigation was applied. In general, the ameliorants did not meet the expectations.
Considering the additional costs of the ameliorant application, and the lack of positive grapevine responses,
this practice cannot be justified under the given, or comparable conditions.

Orographic Effects on Berry Morphology and Chemical Composition of Carignan and Grenache Noir Grapes

A. Sánchez-Ortiz — 2023-11-23

A variation in the climatic parameters of an orographic vineyard influences the growth and development
of vines and grapes. Understanding the effects of this is highly beneficial in determining how viticulture
practices can be modified to enhance grape quality. The aim of this study was to assess the effects of in-row
grape position, altitude and vigour on berry morphology and grape maturity. The effects of vigour, altitude
and in-row grape position on berry weight and diameter, titratable acidity, pH and sugar concentration
of Carignan and Grenache noir grapes grown in a vineyard located in Priorat were investigated in the
2021 vintage. The results show that Carignan grapes with a lower vigour demonstrated a higher sugar
concentration, berry weight and diameter, as well as lower titratable acidity, while the Grenache noir
grapes with a lower vigour achieved only a higher sugar concentration. The grapes at high altitude had a
higher sugar concentration in Carignan and higher titratable acidity in Grenache noir. Outer-row grapes
of Carignan were characterised by lower titratable acidity and a higher sugar concentration, berry weight
and diameter, while the outer-row grapes of Grenache noir displayed lower berry diameter, and a higher
pH and sugar concentration. Vigour and in-row grape position have stronger effects on berry morphology
and chemical composition than altitude. Sugar concentration is more susceptible than other parameters to
be influenced by variability in the vineyard conditions.

The Olfactory Threshold of Rotundone in Brandy is Ten-fold Higher than in Wine and does not Increase with the Complexity of the Matrix

O. Geffroy — 2023-11-23

Rotundone is the only known aroma compound imparting a peppery aroma to wine. Its presence has
recently been documented in spirits, notably those aged in oak barrels. However, the sensory contribution
of rotundone in such alcoholic beverages remains hard to predict, given their high ethanol level. The aim
of this study was to estimate olfactory thresholds for rotundone in brandy using three different matrices.
Rotundone concentrations in the unspiked samples were 50 ng/L for wine distillate and 135 ng/L for brandy,
demonstrating for the first time the presence of rotundone in such spirits and a possible endogenous origin.
The olfactory detection threshold was estimated at 103 ng/L in 40% (v/v) ethanol solution, while difference
thresholds were 171 ng/L and 189 ng/L in fresh wine distillate and young French brandy, respectively, both
standardised at 40% (v/v). These thresholds were 10-fold higher than in wines and did not significantly
differ according to the complexity of the matrix. Our results, which are still preliminary and would deserve
to be validated with a larger number of samples and using a higher number of panellists, open new fields
of investigation for a deeper exploration of the concentration range of rotundone in brandies, particularly
those that underwent a longer ageing period in barrels.

Effect of Irrigation with Treated Municipal Wastewater on Vitis vinifera L. cvs. Cabernet Sauvignon and Sauvignon blanc in Commercial Vineyards in the Coastal Region of South Africa - Vegetative Growth, Yield and Juice Characteristics

K. Hoogendijk — 2023-11-23

A long-term trial was conducted in commercial vineyards in the Coastal region of South Africa to assess the
impact of treated municipal wastewater irrigation on vineyards. Cabernet Sauvignon and Sauvignon blanc
grapevines were irrigated using treated municipal wastewater from the Potsdam wastewater treatment
works for 11 years. Grapevines were either rainfed (RF), irrigated with treated municipal wastewater via
a single dripper line (SLD) or received twice the volume of wastewater via a double dripper line (DLD).
Grapevine responses were measured from the 2013/14 to 2017/18 seasons. Although high amounts of K+,
Na+ and Cl- were applied via wastewater irrigation, it did not result in excessive uptake by plants and
did not affect vegetative growth or yield negatively. Irrigation reduced water constraints throughout the
growing season compared to RF conditions, particularly for Cabernet Sauvignon. Consequently, SLD and
DLD grapevines produced stronger vegetative growth and higher yields compared to RF. Results showed
that the availability of irrigation water (albeit of relatively low quality) in regions where grapevines are
usually grown under dryland conditions can increase grapevine productivity whilst maintaining good
fruit quality. However, the water can vary in its availability as well as its quality over a short period of
time. Plant and soil water status should be monitored regularly to avoid over-irrigation. Implementing
low frequency irrigation scheduling with a sufficient leaching fraction will allow adequate time between
irrigation applications for soils to aerate and organic material to decompose. Irrigation water, soils
and grapevine leaves should be analysed to ensure that chemical parameters conform to recommended
thresholds and norms.

Detection and Quantification of Grapevine Bunch Rot Using Functional Data Analysis and Canonical Variate Analysis Biplots of Infrared Spectral Data

R.J. Cornelissen — 2023-11-23

Grapevine bunch rot assessment has economic significance to wineries. Industrial working conditions
require rapid assessment methods to meet the time constraints typically associated with grape intake
at large wineries. Naturally rot-affected and healthy white wine grape bunches were collected over
five vintages (2013 to 2016, 2020). Spectral data of 382 grape must samples were acquired using three
different, but same-type attenuated total reflection mid-infrared (ATR-MIR) ALPHA spectrometers. The
practical industrial problem of wavenumber shifts collected with different spectrometers was overcome by
applying functional data analysis (FDA). FDA improved the data quality and boosted data mining efforts
in the sample set. Canonical variate analysis (CVA) biplots were employed to visualise the detection and
quantification of rot. When adding 90 % alpha-bags to CVA biplots minimal overlap between rot-affected
(Yes) and healthy (No) samples was observed. Several bands were observed in the region 1734 cm-1 to 1722
cm-1 which correlated with the separation between rot-affected and healthy grape musts. These bands
connect to the C=O stretching of the functional groups of carboxylic acids. In addition, wavenumber 1041
cm-1, presenting the functional group of ethanol, contributed to the separation between categories (severity
% range). ATR-MIR could provide a sustainable alternative for rapid and automated rot assessment.
However, qualitative severity quantification of rot was limited to only discriminating between healthy and
severe rot (> 40 %). This study is novel in applying FDA to correct wavenumber shifts in ATR-MIR spectral
data. Furthermore, visualisation of the viticultural data set using CVA biplots is a novel application of this
technique.