Grapevine Diversity and New Challenges in Grape Production

1. Introduction

Grapes (Vitis genus) is a genus with about 60 to 80 species of vining plants belonging to the family Vitaceae. These plants are native to the north temperate zone and include varieties that may be eaten as table fruit, dried to produce raisins, or crushed to make grape juice or wine. According to the Food and Agriculture Organization (FAO, 2020), 75,866 square kilometers of the world are dedicated to grape production. In addition, about 71% of world grape production is used for wine, 27% as fresh fruit, and 2% as dried fruit.

The Vitis genus is one of the oldest genera in the plant kingdom, and today there are more than 6,000 cultivated varieties of Vitis vinifera distributed across several world regions, particularly in the temperate and subtropical climate regions of the northern and southern hemispheres [1]. This genus comprises between 60 and 70 species, spread mostly throughout North America and Asia, with around 20 and 40 different species, respectively [2]. However, today the Eurasian species Vitis vinifera L. has given rise to most of the grape varieties cultivated in the world.

According to the United States Department of Agriculture and the Natural Resources Conservation Service, there are more than 17 grape species: Vitis acerifolia Raf., Vitis aestivalis Michx., Vitis amurensis Rupr., Vitis arizonica Engelm., Vitis californica Nutt., Vitis cinerea Engelm. ex Millardet, Vitis girdiana Munson, Vitis labrusca L., Vitis monticola Buckley, Vitis mustangensis Buckley, Vitis rotundifolia Michx., Vitis rupestris Scheele, Vitis shuttleworthii House, Vitis tiliifolia Michx. and Bonpl. ex Schult., Vitis vinifera L., Vitis vinifera ssp. sylvestris Hegi, and Vitis vulpina L.

Over the centuries, natural selection, natural crossings, and genetic improvements carried out through various research efforts have generated a wide range of grape shapes, colors, sizes, as well as cluster forms. For example, in terms of shapes, there is a high diversity, such as spherical or round (the most common shape of grapes), oblate, ellipsoidal, obovoid, elongated, and ovoid or oval (Figure 1).

Currently, according to the Vitis International Variety Catalog, there are 21,045 names of cultivars (including 12,250 for Vitis vinifera L.), most of them being wine grapes, which reflects one of their major uses: wine production [3]. However, it is important to note that these numbers also include a considerable number of synonyms and homonyms. Thus, the actual number of vine varieties for Vitis vinifera L. in the world is estimated at 6,000 [3, 4].

Taking into consideration the Global Vine Diversity Report produced by the International Organization of Vine and Wine (OIV), particularly for wine grapes, of the world’s 10,000 known grapevine varieties, 13 cover more than one-third of the world’s vineyard area, and 33 varieties cover 50%. In addition, some grapevine varieties are planted in a high number of countries and thus are called “international varieties.” The most evident example is Cabernet Sauvignon, a variety of French origin (Bordeaux region), which is now one of the most cultivated varieties in the world. This variety is a red wine grape derived from a crossing between Cabernet Franc and Sauvignon Blanc. It is usually characterized by a long maturity period and small berries in small cylindrical-conical-shaped clusters. It also shows a high susceptibility to grapevine trunk diseases (esca, eutypa, and excoriose) and to powdery mildew [5, 6]. Today, its vines are widely distributed across the world, covering an area of 341,000 ha, or 4% of the world’s vineyards, and it is the second most-planted vine variety. It is mainly grown in China, France, Chile, the United States of America, Australia, Spain, Argentina, Italy, and South Africa. Conversely, other varieties, such as Kyoho, may be widely cultivated but only in a small number of countries. In that case, this variety is mainly cultivated in China [7].

The most extensively grown cultivars are, in order, Kyoho, Cabernet Sauvignon, Sultanina, Merlot, Tempranillo, Airen, Chardonnay, Syrah (Shiraz), and Red Globe (Figure 2). Most of these cultivars are red varieties; however, there are three white cultivars included in the group of the most cultivated varieties (Airen, Chardonnay, and Sauvignon Blanc) [7, 8]. Moreover, in recent years, the planting of white varieties has increased because of an intensification in the consumption of white wines. However, the most well-known grapevine cultivars constitute only a small fraction of the vines grown, even in their country of origin.

In each of the main grape- and wine-producing countries, there is a great diversity of grape varieties, and in several of these countries, this diversity of local varieties is highly representative. Table 1 shows the distribution of the different varieties of vines planted in some of the world’s main grape producers, which have greater variability in native varieties. The results indicate that Romania, Italy, Greece, Hungary, and Portugal cultivate especially local varieties, most of them specific to each country. The distribution pattern in each of these countries is totally unique, and, in general, none of their main grapevine varieties accounts for more than 10% of the national vineyard area.

When carrying out a brief analysis of the distribution of the grape varieties, namely local varieties (Table 1), it is observed that for the 10 main varieties grown in Spain, the two most common (Airén and Tempranillo) account for almost half of the national vineyard area (43.2%). Since the early 2000s, there has been significant growth in Tempranillo vineyards (+41.5%), although the national vineyard area has decreased by approximately 15%. For France, three varieties account for one-third of France’s vineyard area: Merlot (the only variety to exceed 100,000 ha), Ugni Blanc, and Grenache Noir.

In Italy, the 10 most planted varieties occupy only 38% of the country’s national vineyard area. In this country, Sangiovese is the top variety and is the only one that occupies more than 50,000 ha. However, in the last 15 years, the total vineyard area of this traditional grape variety has shown a decline of 20%.

Another country with a very high number of native varieties is Portugal, where it is possible to find a great diversity in the vineyard’s composition. The top 10 varieties account for 55% of the country’s national vineyard area. In Portugal, Tempranillo (Aragonez) is the leading variety in terms of surface area. For white grape varieties, Fernão Pires is the variety that leads in terms of vineyard area (Table 1).

Romania’s vine stock is highly diverse. This is because the sum of the areas occupied by Romania’s top 10 varieties amounts to roughly just one-third of the total area under vines. Furthermore, not one of these top varieties accounts for more than 7% of the total surface area. In addition, in this country, it is evident that white grape varieties dominate among the varieties that occupy the largest surface area (Feteasca Regala and Feteasca Alba).

In Greece, three varieties of vines (Savatiano, Roditis, and Sultanina) represent almost 30% of Greece’s vineyard area. The rest of the area is shared between several varieties (native, for the most part), none of which exceeds 3,000 ha, or 3%, of the total. Also, in Europe, Hungarian vineyards are planted with a long list of varieties. The country’s top 10 varieties occupy about half of the total area under vines. The only variety to exceed 10% is Blaufränkisch. The other most cultivated varieties occupy a vineyard area that varies between 2.9% and 5.9% (Table 1). As with most other European countries, Hungary’s vineyard area has decreased by approximately 30% since 2000.

Finally, other important world wine grape producers, such as China, the United States of America, Germany, Argentina, Australia, or South Africa, generally have a greater concentration of grape varieties, with a consequent loss of diversity in the vineyards. In these countries, the 10 most cultivated grape varieties occupy a surface that varies between 60.5% (United States) and 79.9% (Australia) of the total vineyard area.

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2. Global view of grape production

Grapes are the first fruit crops in the world in terms of total value of production, followed by other fruits such as apples, watermelons, bananas, mangoes, and oranges. Today, the cultivation of grapes is widely spread around the world, and the fruit is processed to produce mainly wine and juices and consumed as dried or fresh (table grapes). The distribution of grape production and related products (wine, dried grapes, and juices) is concentrated in certain areas where the geography is favorable. However, it is possible to find grape cultivation in both the northern and southern hemispheres.

Although viticulture has historically evolved in an empirical way, today this economic activity is confronted with a viticulture characterized by high technology to achieve high levels of production and economic profitability. In addition, the production of agricultural goods such as grapes is always subject to outside influences of various factors, such as local climate conditions and access to agricultural solutions. For the first factor, although ideal conditions can vary from one grape varietal to the next (especially when it comes to wine grapes), grapes generally fare best in climates that are warm without being hot. Grapes also require some water availability and moisture to grow well. In addition, grapes require nourishing soil in which to grow, so access to plenty of fertilizer is a key factor. Grapevines are also prone to pests, diseases, molds, and similar problems, so easy access to reliable treatments is imperative. Access to growing technology and supplies such as trellising structures is important, too.

It is important to recognize that grapes, wine, juices, and other related products are an important element of the global food trade. Since the beginning of the century, the export market for these products has experienced remarkable growth. According to the FAO, global exports of fresh table grapes have risen by 74% since 2000, reaching a value of 9.3 billion USD. Similarly, dried grape exports have grown by 56%, now valued at 1.5 billion USD. Wine exports have seen an increase of 67%, climbing to 39.9 billion USD. Global exports of grape juice have expanded by 28%, now standing at 0.8 billion USD [9]. In the specific case of Europe, one of the largest grape-producing areas in the world, European table grape production at producer prices in 2024 shows Spain leading with €1.14 billion, followed by Italy (€0.89616 billion) and Greece (€0.34914 billion). Smaller producers such as Malta contribute €0.00175 billion. Year-on-year changes from 2022 to 2023 highlight significant shifts: France experienced the largest increase at 8.16%, while Hungary saw a decline of 5.72%. Over the longer term, from 2019 to 2024, varied trends emerge with high volatility across different countries [10].

According to the latest OIV State of the Vine and Wine Sector report presented on April 25, 2024, the world’s vineyard surface area continued its decline, shrinking by 0.5% from 2022 to 7.2 million hectares [11]. This trend, observed for the third consecutive year, was driven by the removal of vineyards in major vine-growing regions (including all types of grapes) across both hemispheres. In 2023, the top six countries represented 56% of the world total, while the European Union and the southern hemisphere accounted for 45% and 12%, respectively. In addition, fresh grape production in 2023 was about 74.7 million tonnes, while dried grape production amounted to 1.15 million tonnes. Table grape production was approximately 32 million tonnes. Thus, almost the total volume of grapes produced in the world is used for processing and manufacturing wine and juices.

Although there continues to be a trend toward some growth in grape production in several geographical areas, it cannot be forgotten that this is a crop that is very dependent on environmental conditions. Thus, one of the most dominant environmental constraints is water shortage, inducing some degree of drought stress during the growing season. In this way, as a result of its climate dependence, the future of grape production and all its derivative products will be strongly linked to predicted changes in climatic factors, namely temperature increase, precipitation variation, and carbon dioxide concentration [12–14].

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3. Climate changes and grape production

Normally, grapevine cultivation requires mean air temperatures ranging from 12°C to 22°C during the growing cycle, 600–800 mm of rainfall (or sufficient irrigation), a frost-free growing season, and at least 700–900 μmol photons m⁻² s⁻¹ solar radiation [15, 16]. However, there is a high diversity of challenges that could affect viticulture activity. In fact, grapes are cultivated on most continents, whether in the northern hemisphere (between 4° and 51° of latitude) or the southern hemisphere (between 6° and 45° of latitude). In this way, all viticultural activity develops across a large multiplicity of different climates and soil conditions. For climates, it is possible to find viticultural activity in regions with a typically Mediterranean climate, but also in climates such as cold continental oceanic, warm oceanic, transition temperate, continental, subtropical, attenuated tropical, and arid climates. In all these regions, a major change in environmental conditions can be observed, regardless of the type of climate characteristic of the region. These changes are now affecting vine productivity, but also grape composition, namely the sugar content and acidity concentrations [17, 18]. For other components, such as polyphenols or aroma compounds, their relationships to environmental changes could be more difficult to identify. On the other hand, different grape varieties may also have different responses to the great variability in environmental conditions [19].

According to several investigations, in recent decades, climate changes have been shown to affect grapevine phenology, physiology, and their biochemistry [19–21]. However, the geographic location of viticultural activity is also changing due to climate changes [22]. In fact, according to several authors, in the last two decades, viticultural activity in the Northern Ecuadorian highlands has expanded vineyard areas by between 200 and 300 m of altitude as an adaptive response to changes in growing environments driven by global climate change, particularly related to the increase in temperature [23]. These location movements to higher altitude regions, where it is possible to have lower mean air temperatures, higher thermal amplitude, and global radiation exchange, have become an alternative for maintaining the quality of the vines cultivated, particularly to preserve the productivity and quality of the grapes obtained, such as their acidity and aroma composition [24–26].

Climate conditions, especially air temperature, are among the most important factors that can affect vine growth, productivity, and grape quality. With the global temperature increase, there is an increment in the vine vegetative and reproductive cycle. In general, temperatures above 35°C induce a reduction in photosynthesis in leaves and tend to reduce the quality of grapes and wines, as they accelerate the accumulation of sugar in grape berries, increasing their alcohol content. At the same time, there is a reduction in acidity due to the rapid depletion of organic acids [27]. In addition, under very high temperatures associated with intense solar radiation, it is possible to produce damage to the pedicel and rachis, with a consequent wilting of entire sections of the bunch [28–30]. However, according to Alston et al. [31], several cultivation practices introduced in the vines, such as crop load reduction, water deficit, and various canopy management strategies, may have also contributed to the increase in sugar content at harvest more than changes in the climate.

It is also important to note that different grape varieties may have different responses to global warming. Thus, according to Dunn [32], the Riesling variety, with an increase in temperature from 20°C to 30°C, showed an improvement in the weight of bunch primordia (preformed inflorescences in the latent winter buds) fourfold, while Shiraz was unaffected. In another study, this last grape variety showed a very low response in basic yield components under experiments where it was subjected to an increase of 4°C in warming [33]. Also, between the red and white varieties, there seems to be a different tolerance to warm conditions. In general, red varieties appear to tolerate warm conditions better than white varieties. Sadras et al. [34] analyzed the time trends (1980–2005) in 24 grape-growing regions from Australia according to long-term daily mean temperatures during the month before harvest (which varied from 14.7°C in Southern Tasmania to 24.2°C in Swan Valley). These authors reported a positive correlation between quality ratings and daily mean regional temperature in different Australian regions for red wines but not for white wines. However, there are contradictory data related to the impact of warming on the different cultivars, especially in grape quality. Other authors reported that a white variety, such as Chardonnay, responded positively to an increase in temperature [35].

It is now clear that climate changes will induce an increase in climate risks associated with more frequent and intense heat stress, which can damage grapevines and reduce wine quality. However, for several wine regions, data suggest a reduction in the risks associated with freeze damage. This is particularly evident and potentially beneficial for wine regions with cool climates, such as Canada or several regions in Northern Europe. In addition, for several Mediterranean regions, the risk of late frost will also be reduced due to the increase in temperatures. Thus, there will be climatic margins for the development of viticulture in several different regions, which can be considered a benefit resulting from the gradual warming trend [36, 37]. Petriashvili et al. [38] reported that warming will lead to an increase in vine area in the Czech Republic, particularly for red varieties. This is thanks to climate change, as over the last 60 years, the average temperature in the wine regions of this country has increased by one-and-a-half degrees Celsius. Warming manifests itself mainly in autumn, when the grapes ripen, and the oscillation of warm days and cold nights will have a positive impact on higher amounts of aromatic substances. However, in other countries or regions, global warming will have very negative impacts on viticulture in the future, not only for red varieties but also for white varieties. Thus, it is possible to conclude that climate change will produce “winners” and “losers,” with the “winners” being the regions closer to the north, while the “losers” will be the southern regions, such as several European wine regions in the Mediterranean basin.

In Southern Europe, and in general for the entire Mediterranean region, a significant temperature increase and drying trends are expected. In these regions, more frequent and severe droughts are projected, with successive record – breaking lengths of consecutive dry day episodes [39]. As such, increasing temperatures in these areas can accelerate the plant development rate, thus advancing the occurrence of phenological stages and their corresponding timings. Several authors have reported that under ongoing global warming, earlier phenological timings with shortened growing phenophases will occur. Additionally, the magnitude of the advancement in phenological phases due to the warming trend will depend on the grape variety [40, 41]. These advancements are projected to have varying impacts on grape variety yield, grape berry composition, and consequently, wine quality. According to several authors, in Spain, the Tempranillo variety cultivated in the Ribera del Duero, Rioja, and Toro wine regions is projected to consistently undergo earlier flowering stages by 6–10 days, 3–8 days, and 6–8 days in 2050, and by 8–16 days, 5–12 days, and 7–12 days in 2070, respectively. The earlier flowering stage is also accompanied by shortened phenophases in these regions, such as flowering–veraison and veraison–maturity [42–44]. Considering these earlier phenological timings, grape ripening will occur under excessively high temperatures, where berries can accumulate undesirable low organic acids, inducing high pH values, very low total acidity, high sugar contents, and, at the same time, a potentially low concentration of phenolic compounds (e.g., flavonoids and anthocyanins) [40, 45]. Vršič et al. [46] studied the development trends of bioclimatic parameters in several Slovenian regions from 1952 to 2022 and the dynamics of grape ripening in early-, medium-, and late-ripening grape varieties. These authors reported that, as a result of climate warming, grapes in northeastern Slovenia ripened 26 days earlier for “Sauvignon Blanc”) and 35 days earlier for “Welschriesling.” In addition, a decrease in total acidity and an increase in sugar content in the berries were detected, which can be attributed to the higher temperatures during the growing season, especially during the ripening period of the grapes. However, for other grape varieties with late ripening such as “Riesling” and “Furmint,” high temperatures had a positive effect on the lower total acidity. Thus, changing plant material and cultivation techniques that retard maturity could be an effective adaptation strategy to higher temperatures, but only up to a certain level of warming.

Climate change not only determines changes in air temperature but also could induce significant changes in precipitation, humidity, radiation, and CO₂. Thus, increased drought reduces yield and can result in sustainability losses. The use of drought-resistant plant material and the adoption of different training systems are effective adaptation strategies to deal with declining water availability. Supplementary irrigation is also an option when sustainable freshwater resources are available. However, in several wine regions across the world, it is expected that the quantity and quality of water available for irrigation will be reduced.

In warm and dry regions, rising temperatures are increasing the vine water demand. In that case, both heat and water stress limit crop yield, and in extreme cases, it can cause problems with the plant’s survival. In addition, even under moderate water stress, there are limits to canopy gas exchange and growth, which result in more sun-exposed and warmer bunches, leading to smaller berries and altered grape composition [46].

Veselá et al. [47] confirmed the effect of total precipitation changes on the value of vine production in the Czech Republic, while Meggio [48] concluded that, for several grape varieties (Merlot, Cabernet Sauvignon, Glera, and Garganega), the precipitation during the warmest month and temperature anomalies during late spring (May–June) and during the warmest month (August) will be important factors in understanding the effect of climate change on grape sugar ripeness.

It is not just the reduction in precipitation that can be associated with climate change. A modification in rainfall patterns is another change that occurs as a result of climate change. In fact, climate change may alter the characteristics of precipitation, such as intensity, frequency, and duration of rain, even if it does not alter the total amount of precipitation. Di Carlo et al. [49] show that precipitation intensity could induce an early grape harvest date. These authors found in Italy that for growing seasons since 1960, annual harvest dates have been getting earlier as average monthly temperature increases (−5.92 days °C⁻¹) and at the same time with more intense precipitation events (−1.51 days mm⁻¹). Thus, these data may generate the hypothesis that the increasing tendency of precipitation intensity could exacerbate the effect of global warming on viticulture.

The prominence and emergence of pests and diseases, along with the increasing occurrence of extreme weather events such as heatwaves, heavy rainfall, and possibly hail, also challenge grape production in some regions. In contrast, other areas might benefit from reduced pest and disease pressure. However, precipitation, and particularly its temporal distribution during specific stages of grape maturation, could engender the development of drowned vines as a result of excessive humidity levels. Mira de Orduña [50] reported that climate change, especially high temperatures, determines the vectors responsible for the distribution of several diseases. In that case, an important disease that may move poleward is Pierce’s disease, which is caused by Xylella fastidiosa. Warmer winter temperatures may encourage the northern distribution of the vector and/or pathogen of this vine disease [51].

The conditions of high temperatures and precipitation will also overstimulate the growth of vegetation, creating denser canopies and a higher likelihood of promoting several plant diseases [52].

Very high levels of precipitation, particularly in short periods of time, and extreme weather can contribute to soil erosion and degradation (particularly related to chemical composition and microbial populations), impacting the sustainability of all vineyard systems. According to Schultz [53], rising temperatures in the upper soil layers could have an impact on the distribution of microbiological populations. These changes contribute to the decrease of organic matter and the storage capacity of organic carbon in soils.

Solar radiation and the increase in atmospheric CO₂ concentration are other abiotic factors that are changing during global warming, with the latter being one of the factors that has contributed most to this warming. The vine is a resilient crop to solar radiation; however, grapes are sensitive to exposure to high solar radiation, leading to fruit damage, such as the appearance of brown/necrotic spots on the epidermis of the grapes and the complete desiccation of the berries. On the other hand, an excessive amount of light induces the production of triplet chlorophyll and reactive oxygen species, including superoxide anion, hydrogen peroxide, and hydroxyl radicals. These processes promote oxidative stress in the vine photosystems [29]. According to Fernandes de Oliveira and Nieddu [54], in the Mediterranean region, red grapes can adapt their growth and physiological responses to high natural UV and temperature. However, the accumulation of anthocyanins and other phenolic substances can vary considerably according to the sensitivity of cultivars to these abiotic factors. Several authors have reported that grape skin phenolic content increases as a result of grape exposure to direct radiation. However, grape exposure could modify the abundance of grape aromas and aroma precursors [55].

Figure 3 schematically illustrates several challenges resulting from climate change in viticulture, along with possible mitigation strategies in vineyards and wine production.

All these potential negative consequences of climate change can be mitigated through adaptations in the vineyard. Later-ripening varieties and clones can be the answer to higher temperatures, while drought-resistant varieties and rootstocks can address increasing water deficits. In addition, changes in the training system could be another option for canopy management. All management strategies include a range of techniques used in vineyards to create a balance between reproductive activity and vegetative development, ultimately improving the quality of the fruits produced. For this, several techniques related to trellising/training, canopy hedging, cluster thinning, basal leaf removal, shading/netting, dormant pruning, shoot placement, and shoot thinning could be adequate strategies to achieve a proper balance between vegetative development, grape yield, and quality parameters under conditions where the climate is continually changing [56–59]. Torres et al. [56] studied the optimal ranges of berry solar radiation exposure for the regulation of flavonoid biosynthesis and how canopy management practices could affect grape berry composition in the Cabernet Sauvignon variety. According to these authors, the best results (namely for °Brix) were obtained in experiments where 24 shoots were thinned per vine. Other researchers compared six trellis systems with three levels of applied water amounts based on different replacements of crop evapotranspiration over two consecutive seasons [57]. The treatments included a vertical shoot position, two modified vertical shoot positions, a single high wire, a high quadrilateral, and a Guyot-pruned vertical shoot position combined with 25%, 50%, and 100% ETc water replacement. The results indicated that the single high wire led to greater yield, while the vertical shoot position resulted in an increase in berry flavonol concentration. Additionally, the irrigation treatments revealed linear trends for yield components, where greater applied water resulted in larger berry size and, consequently, greater yield.

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4. Recent technologies apply to grape production

In recent years, one of the main innovations has been related to the genetic improvement of grapevines to increase their resistance to pests and diseases. This is because classical Vitis vinifera cultivars are relatively vulnerable to several diseases, such as mildew, and insect damage, which have increased in recent years due to climate change. Thus, in recent years, several disease-resistant hybrid grape cultivars have been developed. These hybrids are crosses between V. vinifera cultivars and wild species of Vitis, between V. vinifera cultivars and hybrid grapes, or between hybrid cultivars [58]. These hybrids have been bred to be resistant to diseases such as fungal and bacterial infections, insect pests, and/or extreme cold [59, 60]. However, wines made from these hybrids (totally or partially) can have unusual characteristics, which in many markets are still not widely appreciated by consumers [61]. These wine characteristics are associated with unusual “foxy” aromas [62], high titratable acidity, and low condensed tannin content [63]. Other studies have described that these wines exhibit relatively high pH values compared to Vitis vinifera wines, which makes them more vulnerable to microbial spoilage [64].

The introduction of robots to carry out several operations in the vineyard has been an area that has developed as a way of increasing efficiency and productivity. Thus, whether as prototypes or as fully operational equipment, robots have been introduced into grape harvesting [65, 66]. For example, Jiang et al. [65] developed a robot capable of performing multi-target spatial information extraction with a single camera, obtaining information on the coordinates of spatial points about the location of the grape bunches on the vine to carry out precise harvesting. The results obtained demonstrated that when the degree of shading of the leaves was 21–40%, the success rate of harvesting the bunches was 73.3%, and the harvest time of a bunch of grapes was 8.66 seconds. These data met the requirements of rapid location identification and low harvest loss of grape bunches in a real horizontal trellis environment. Also, in vineyard mapping and pruning, the use of robots can contribute to increased work productivity [67]. These robots are used to prune the vines with high precision and collect data on vine health and growth using an integrated system that includes machine vision, thermography, and fluorescence-based sensors. In addition to contributing to greater efficiency in grape production, robotic systems can also help to reduce the environmental impact of viticulture by decreasing fossil fuel consumption [68, 69].

In recent years, there has been a rising interest in precision viticulture. This production system leverages a wide range of information technologies to understand variability in production systems and map variability within vineyards in order to target management according to the real needs of each part of the field. According to Tardaguila et al. [70], precision viticulture requires a three-step cyclical process: data acquisition from the vineyard; information extraction from the acquired data; and development/implementation of a targeted management plan based on the previous critical analysis. Figure 4 shows several new strategies for grape production and monitoring of the entire vineyard ecosystem using new technological options.

In modern and precision viticulture, several tools, such as soil proximal (ground) or weather sensors, remote sensing (satellite, airborne, or drone-UAVs remote sensing), global navigation satellite system, geographical information systems, and robotics, can be used. The variability in viticulture and in a particular vineyard can be due to any difference in any element or property for each of the natural, biological, or agronomic factors which influence vine performance and the expression of grape character or composition.

In precision viticulture, several technologies have been developed, particularly the use of non-invasive digital technologies. These technologies could help manage various viticultural practices, including the installation of new vineyards or their reinstallation, as well as the harvest process, to contribute to an increase in yield production and grape quality. For this purpose, a wide range of sensor technologies, including spectroscopy, multispectral and hyperspectral imaging (HIS), chlorophyll fluorescence, thermography, electrical resistivity, laser imaging detection and ranging, and computer vision, can be used for remote or close monitoring. For example, several non-invasive technologies can be utilized for disease detection in grapevines (Table 2).

Thus, the use of some of these non-invasive sensing technologies can be used in wine or table grape production to obtain key information about the vineyard and the composition and quality of the grapes produced. To collect this information, portable sensors or sensors embedded in ground-based platforms such as piloted vehicles, autonomous robotic systems and machinery, or aerial platforms such as satellites, light aircraft, and UAVs or drones [84] are used. Regardless of the technology used, the main objective of vineyard monitoring using sensors is to collect a large amount of georeferenced information and data, which can be measured using a wide range of sensors. For this purpose, there is a vast number of sensors that can be used in precision viticulture, namely RGB cameras, multispectral, hyperspectral, thermal, and light detection and ranging (LiDAR) sensors. In general, the most used sensors are multispectral sensors [85].

RGB cameras are used with the aim of identifying vine canopy, shoots, or bunches. RGB sensors include wavelengths of blue (450–490 nm), green (520–560 nm), and red (635–700 nm). With the use of these sensors, it may be possible to calculate RGB indices to enhance the vegetation of the vineyard from the overall image [86]. Using multispectral imaging sensors, it is possible to record the radiation reflected by vines in a small number of broad bands, between 2 and 8, usually for certain wavelengths that enable the detection of stress conditions [87]. According to Guo et al. [88], these images can be used to calculate vegetation indices, which are useful in monitoring vegetation phenology. These vegetation indices are considered a potential screening tool to determine the plant status, such as nitrogen, chlorophyll content, and green leaf biomass.

Using hyperspectral cameras, it is possible to combine spectroscopy and imaging techniques, providing spatial and spectral information. Thus, with these sensors, it is possible to detect numerous closely spaced wavelength ranges and obtain reflectance, transmittance, and emissivity information in bands with spectral resolution [89]. The greater the number of bands, and consequently the smaller their width, the more this technology demonstrates the ability to identify specific components or elements of a culture based on its reflectance characteristics. Using hyperspectral technology, images can be collected in a wavelength range of 400–2,500 nm with variable spectral resolution, expressed in nm, and high spatial resolution [90]. According to several published works, hyperspectral sensors have been used to characterize water status by calculating different indices [91, 92]. These sensors can also be used to obtain hyperspectral images of berries, contributing to the analysis of grape quality through non-destructive detection methods. Thus, using these methodologies, it is possible to quantify soluble solids, anthocyanin content from red grapes, and other important parameters related to grape composition, such as total polyphenols, titratable acidity, or malic acid content [85, 93]. In general, the relevant wavelengths are included in the visible region at 454, 625, 646, and 698 nm.

Generally, the use of thermal imaging cameras is another option that can be used in precision viticulture. Thus, by measuring the foliar emissivity acquired in the thermal infrared spectra, the water stress related to leaf temperature can be calculated. Therefore, through the estimation of the Crop Water Stress Index (CWSI), the value can vary between 0 and 1, indicating stressful and well-irrigated conditions, respectively [94]. Finally, LiDAR systems could be used for measurements of primary canopy attributes, such as height, width, and distance between rows, to generate integrative canopy indicators such as leaf wall area or tree row volume. These systems can collect spatial information of one-dimensional (1D), two-dimensional (2D), and three-dimensional (3D) types with the use of optical scanning systems [95, 96]. According to several published data, the 2D laser scanner surveys showed a significant relationship with pruning weight (r = 0.80), yield, and vigor indices, showing the potential of using laser scanner measurements to assess the variability of vine vigor within vineyards. In addition, the evaluation of canopy characteristics, such as height, width, and density measured using laser scanning technology, can provide relevant information to improve several viticultural practices, namely the agrochemical spray treatments in the vineyards [97–99].

Thus, the use of different sensing technologies in vineyards is an important factor to monitor a great number of key aspects related to grape production. These technologies could be very relevant in different areas, such as improving and understanding soil properties and topography, vegetative growth, canopy architecture, nutrient and water status, pest and disease diagnostics and their control, crop forecasting, yield and grape composition, vineyard sampling, targeted management, and selective harvesting.

For soil properties and topography, several works have reported the use of proximal soil sensors that can be mounted on mobile platforms to acquire geo-referenced soil data on-the-go. In this case, the high-resolution maps obtained provide insight into the spatial variability of soil properties and elevation at scales that are relevant when new vineyards are planted or existing vineyards are restructured [100, 101]. In addition, other sensors, namely optical and electrochemical sensors, could be used to study the chemical soil fertility parameters, the presence of specific minerals, and changes in soil texture [102, 103].

To analyze and carry out proper monitoring of vegetative growth, nutritional status, and canopy architecture, recently, new approaches for estimating canopy biomass and detecting missing plants have been developed using RGB imagery acquired by UAV platforms [104]. In addition, canopy architecture, which includes fruit and leaf exposure, can be evaluated using machine vision technologies, such as RGB imagery [105, 106]. Also, the development of smartphones and “apps” allows information to be obtained quickly and easily; while increasing the portability of analyses and decisions, it is a trend that has been developing. In this context, several apps have been developed to measure vine performance attributes such as canopy vigor, LAI, and porosity [107].

With climate change, and particularly global warming, assessing vine water status and irrigation management is essential for adequate monitoring of the plant’s hydric status and for obtaining high grape production in both quantitative and qualitative terms. Thus, thermal imaging is one of the most powerful non-invasive technologies for evaluating vineyard water status. This technology can be applied to determine water status manually or remotely using UAVs or other aerial platforms [108–110]. Gutiérrez et al. [111] developed an on-the-go thermal imaging application for the assessment and mapping of vineyard water status, building a dataset from a commercial Tempranillo (Vitis vinifera L.) vineyard and validating it in another commercial vineyard from a different winegrowing region. In this study, thermal imaging was performed with a thermal camera mounted on an all-terrain vehicle (moving at 5 km/h and operating at a distance from the canopy of 1.20 m). These researchers used stem water potential (Ψ_stem) for validation as the grapevine water status reference method, employing a Scholander pressure chamber. In addition, the CWSI and stomatal conductance index (I_g) from a four-day dataset were computed and correlated with Ψ_stem, delivering significant determination coefficients R² of up to 0.71. The predicted values of both indices were thus employed for mapping vineyard water status in the second plot. The results demonstrate the potential applicability of on-the-go thermal imaging for assessing and mapping water status in vineyards. Furthermore, the use of NIR (750–2500 nm) spectroscopy is another option to assess real-time plant water status under field conditions [112]. On the other hand, the use of the spectral range is another option that could be employed to measure grapevine water status and its variability within a vineyard [113]. Another possibility was studied by Brillante et al. [101], where electrical resistivity (ER) was used to measure plant-available soil water variables, that is, available soil water (ASW), total transpirable soil water (TTSW), and fraction of transpirable soil water (FTSW). According to the results obtained by these authors, the models assessed had good predictive performance and were therefore used to map ASW, TTSW, and FTSW in the vineyard. ER coupled with machine-learning algorithms was shown to be a good proxy for the quantification and visualization of plant-available soil water with low disturbance.

Recently, several non-invasive sensors to measure attributes of grape berry quality and composition have been developed and used in modern viticulture. Gutiérrez et al. [114] used HSI to assess grape composition, namely by measuring total soluble solids and anthocyanin content in grapes in real time in the vineyard. Regression models of total soluble solids had determination coefficients (R²) of 0.91 for a fivefold cross-validation and 0.92 for the prediction of external samples. For anthocyanin concentration, R² values of 0.72 for cross-validation and 0.83 for prediction were achieved. The results obtained by these authors suggest that the potential use of on-the-go HSI to automate the assessment of important grape compositional parameters in vineyards is a promising technique. In addition, the use of NIR spectroscopy could be a new, fast, and non-destructive method based on HIS to fingerprint the color pigments of whole grape berries [115]. Recently, Tsakiridis et al. [116] directly applied HIS in the field to analyze the sugar content (^◦Brix) of four grape varieties, namely Chardonnay, Malagouzia, Sauvignon-Blanc, and Syrah. The results demonstrated a good adequacy of the technique compared to those obtained in a laboratory environment. Other works have demonstrated NIR spectral analyses as an alternative option for monitoring dynamic changes in grape berry composition during the ripening period and hence provide an alternative to destructive and wet chemistry procedures [117].

Thus, using all these recent technologies, grape producers can acquire a large amount of information with great flexibility in the timing of data acquisition. These capacities and the data collected allow grape growers to apply inputs such as fertilizers, sprays, and irrigation water in a more efficient way, responding more effectively to the physiological needs of the vines, thus contributing to greater productivity, performance, and efficiency. On the other hand, it is still possible to obtain information that allows selective grape harvesting or harvesting parcels according to the different qualitative and quantitative requirements.

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5. Conclusions

Grape production activity currently faces a vast and complex set of challenges. Although the vine is a plant with a high diversity of species and subspecies, dispersed across different geographies, climate change is a huge challenge for its development and economic exploitation. However, climate change in several regions could also be an opportunity for new latitudes further north to have conditions for the development of grape production in the near future, leading to new challenges in the sector. On the other hand, investing in existing genetic diversity with the aim of increasing the adaptability of different varieties to the soil and climate characteristics of different regions and contributing to the production of wines with new profiles accepted by consumers will be fundamental challenges for the success of the grape production sector. The development of new hybrid varieties resulting from the crossing of several subspecies could increase not only the resilience of the vine, in the face of new climatic conditions, but also the vine’s resistance to diseases and its productivity. In this way, biotechnology and genomics have the potential to revolutionize grape breeding and disease resistance.

Finally, one of the most revolutionary changes in viticulture is the adoption of precision agriculture. Using a combination of GPS, satellite imagery, and smart sensors, vineyards can now be managed with exceptional accuracy. These technologies allow grape producers to monitor variables such as soil composition, moisture levels, and vine health across different sections of the vineyard. The use of GPS-guided equipment, the introduction of smart irrigation systems that adjust water distribution based on the immediate needs of the vines, and the use of artificial intelligence and data analytics are examples of new technologies that can be used by grape producers. All these technologies analyze vast amounts of information gathered from sensors, drones, and weather stations to help producers make better decisions.

Thus, all these challenges and the constant changes that are being introduced in grape production mean that this agricultural activity is permanently facing significant challenges to increase the productivity and quality of the grapes produced.