Research Articles (Viticulture and Oenology)

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Infrared spectroscopy and chemometric applications for the qualitative and quantitative investigation of grapevine organs
(Frontiers Media S.A, 2021-09-03) Van Wyngaard, Elizma; Blancquaert, Erna; Nieuwoudt, Hélène; Aleixandre-Tudo, Jose Luis
The fourth agricultural revolution is leading us into a time of using data science as a tool to implement precision viticulture. Infrared spectroscopy provides the means for rapid and large-scale data collection to achieve this goal. The non-invasive applications of infrared spectroscopy in grapevines are still in its infancy, but recent studies have reported its feasibility. This review examines near infrared and mid infrared spectroscopy for the qualitative and quantitative investigation of intact grapevine organs. Qualitative applications, with the focus on using spectral data for categorization purposes, is discussed. The quantitative applications discussed in this review focuses on the methods associated with carbohydrates, nitrogen, and amino acids, using both invasive and non-invasive means of sample measurement. Few studies have investigated the use of infrared spectroscopy for the direct measurement of intact, fresh, and unfrozen grapevine organs such as berries or leaves, and these studies are examined in depth. The chemometric procedures associated with qualitative and quantitative infrared techniques are discussed, followed by the critical evaluation of the future prospects that could be expected in the field.
Calibration of the surface renewal method (SR) under different meteorological conditions in an avocado orchard
(MDPI, 2020-05-19) Moran, Andres; Ferreyra, Raul; Selles, Gabriel; Salgado, Eduardo; Caceres-Mella, Alejandro; Poblete-Echeverria, Carlos
The surface renewal method (SR) allows estimating the sensible heat flux (H) using high-frequency thermocouples. Traditionally, SR has been compared and calibrated using standard instruments such as the Eddy covariance system (EC). Calibration involves correcting H measured with SR (H’SR) by means of the calibration factor (α). However, several studies show that α is not constant and could depend on canopy architecture, measurement height, atmospheric stability, and weather conditions. In avocado orchards, there is not enough information about energy fluxes and the application of the SR method. Therefore, the objective of this study is to calibrate the SR method in a mature avocado orchard considering the effect of meteorological conditions on the determination of α. The components of the surface energy balance were measured using an EC system in a commercial avocado orchard (cv. Hass) located in the Aconcagua Valley, Valparaíso Region, Chile. To evaluate the effect of the meteorological conditions on the determination of α, the dataset was classified into nine categories based on solar radiation and wind intensity. The results show that α varies according to meteorological conditions, with significant differences for cloudy days. The use of the variable α reduced the error in estimating H, so, this methodology can be used to have a more precise approximation of the energy balance and therefore to the water requirements.
Effect of missing vines on total leaf area determined by NDVI calculated from sentinel satellite data : progressive vine removal experiments
(MDPI, 2020-05-23) Velez, Sergio; Barajas, Enrique; Rubio, Jose Antonio; Vacas, Ruben; Poblete-Echeverria, Carlos
Remote Sensing (RS) allows the estimation of some important vineyard parameters. There are several platforms for obtaining RS information. In this context, Sentinel satellites are a valuable tool for RS since they provide free and regular images of the earth’s surface. However, several problems regarding the low-resolution of the imagery arise when using this technology, such as handling mixed pixels that include vegetation, soil and shadows. Under this condition, the Normalized Difference Vegetation Index (NDVI) value in a particular pixel is an indicator of the amount of vegetation (canopy area) rather than the NDVI from the canopy (as a vigour expression), but its reliability varies depending on several factors, such as the presence of mixed pixels or the effect of missing vines (a vineyard, once established, generally loses grapevines each year due to diseases, abiotic stress, etc.). In this study, a vine removal simulation (greenhouse experiment) and an actual vine removal (field experiment) were carried out. In the field experiment, the position of the Sentinel-2 pixels was marked using high-precision GPS. Controlled removal of vines from a block of cv. Cabernet Sauvignon was done in four steps. The removal of the vines was done during the summer of 2019, matching with the start of the maximum vegetative growth. The Total Leaf Area (TLA) of each pixel was calculated using destructive field measurements. The operations were planned to have two satellite images available between each removal step. As a result, a strong linear relationship (R2 = 0.986 and R2 = 0.72) was obtained between the TLA and NDVI reductions, which quantitatively indicates the effect of the missing vines on the NDVI values.
Seeing the forest through the (phylogenetic) trees : functional characterisation of grapevine terpene synthase (VviTPS) paralogues and orthologues
(MDPI, 2021-07-26) Smit, Samuel J.; Vivier, Melane A.; Young, Philip R.; Nussbaumer, Thomas; Seetharam, Arum
Gene families involved in specialised metabolism play a key role in a myriad of ecophysiological and biochemical functions. The Vitis vinifera sesquiterpene synthases represent the largest subfamily of grapevine terpene synthase (VviTPS) genes and are important volatile metabolites for wine flavour and aroma, as well as ecophysiological interactions. The functional characterisation of VviTPS genes is complicated by a reliance on a single reference genome that greatly underrepresents this large gene family, exacerbated by extensive duplications and paralogy. The recent release of multiple phased diploid grapevine genomes, as well as extensive whole-genome resequencing efforts, provide a wealth of new sequence information that can be utilised to overcome the limitations of the reference genome. A large cluster of sesquiterpene synthases, localised to chromosome 18, was explored by means of comparative sequence analyses using the publicly available grapevine reference genome, three PacBio phased diploid genomes and whole-genome resequencing data from multiple genotypes. Two genes, VviTPS04 and -10, were identified as putative paralogues and/or allelic variants. Subsequent gene isolation from multiple grapevine genotypes and characterisation by means of a heterologous in planta expression and volatile analysis resulted in the identification of genotype-specific structural variations and polymorphisms that impact the gene function. These results present novel insight into how grapevine domestication likely shaped the VviTPS landscape to result in genotype-specific functions.
Basic in-mouth attribute evaluation : a comparison of two panels
(MDPI, 2018-12-21) Mihnea, Mihaela; Aleixandre-Tudo, Jose Luis; Kidd, Martin; Du Toit, Wessel
Astringency is often difficult to evaluate accurately in wine because of its complexity. This accuracy can improve through training sessions, but it can be time-consuming and expensive. A way to reduce these costs can be the use of wine experts, who are known to be reliable evaluators. Therefore, the aim of this work was to compare the sensory results and the panel performance obtained using trained panelists versus wine experts (winemakers). Judges evaluated twelve red wines for in-mouth basic perception (sweet, sour, bitter, astringent, and burning sensation) following the same tasting protocol and with the samples being presented in two different tasting modalities. Panels’ performance and relationship between the chemical composition and the sensory perception were investigated. Both panels showed similar consistency and repeatability, and they were able to accurately measure the astringency of the wines. However, the significant correlations between sensory scores and chemical composition varied with the panel and the tasting modality. From our results, we could see that winemakers tended to discriminate better between the samples when the differences were very small.

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