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Article

Airborne Plasmopara viticola Sporangia: A Study of Vineyards in Two Bioclimatic Regions of Northwestern Spain

by
Lucía Carrera
1,
María Fernández-González
1,*,
María Jesús Aira
2,
Kenia C. Sánchez Espinosa
1,
Rosa Pérez Otero
3 and
Francisco Javier Rodríguez-Rajo
1
1
Department of Plant Biology and Soil Sciences, Faculty of Sciences, University of Vigo, 32004 Ourense, Spain
2
Department of Botany, Faculty of Biology, University of Santiago de Compostela, C/Lope Gómez de Marzoa, s/n, 15782 Santiago de Compostela, Spain
3
Phytopathological Station Areeiro, Subida a la Robleda, s/n, 36153 Pontevedra, Spain
*
Author to whom correspondence should be addressed.
Horticulturae 2025, 11(3), 228; https://doi.org/10.3390/horticulturae11030228
Submission received: 22 January 2025 / Revised: 10 February 2025 / Accepted: 18 February 2025 / Published: 20 February 2025
(This article belongs to the Special Issue Advances in Disease Diagnostics and Pathogen Biocontrol of Horticulture Crops)
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Abstract

:
Downy mildew, caused by Plasmopara viticola, is one of the most destructive diseases affecting grapevines, particularly in areas with bioclimatic conditions that favor its development, such as northwestern Spain. This study examined the presence of P. viticola sporangia in three vineyards located in two distinct bioclimatic regions (ultra-oceanic and subcontinental) over two consecutive years (2023 and 2024) using Hirst-type volumetric samplers. The relationship between P. viticola and grapevine phenology, along with meteorological variables, was analyzed to help develop effective strategies for managing this disease. Spearman correlation analysis showed that temperature was the most influential variable in all vineyards. However, water-related variables (relative humidity and precipitation) showed stronger correlations in the ultra-oceanic vineyard, which also had the highest sporangium concentrations. Principal Component Analysis revealed that sporangium concentrations in the ultra-oceanic region were most strongly associated with relative humidity and wind speed. In contrast, sporangium concentrations in the subcontinental vineyards were more closely related to temperature, dew point, and wind speed (in Alongos), as well as wind speed (in Alongos and Cenlle). PCA results clearly differentiated the two bioclimatic zones. These findings provide valuable insights that can improve downy mildew management in vineyards in northwestern Spain.

1. Introduction

The grapevine (Vitis vinifera L.) is known for its significant agricultural and economic value in various geographical regions [1], with Spain being the world’s leading wine exporter by volume and the third by value [2,3]. The northwestern region of the country has over 33,200 hectares of vineyards, with the vast majority of wine production centered in the provinces of Ourense and Pontevedra [4]. The bioclimatic conditions in this area are characterized by high humidity, abundant rainfall, and moderate temperatures, all propitious to the development of downy mildew (Plasmopara viticola) on grapevines, one of the most devastating diseases affecting these crops [5,6,7]. Downy mildew epidemics result in both direct and indirect yield losses, including reduced photosynthetic activity in affected leaves, the premature defoliation of vines, and the rotting of inflorescences, shoots, and clusters [8].
The causal agent of this disease is the oomycete Plasmopara viticola (Berk. & M.A. Curtis) Berl. & De Toni, which was brought to Europe in 1878 from North America through rootstock of American wild grapevines resistant to phylloxera [9]. P. viticola is an obligate parasite belonging to the family Peronosporaceae, the order Peronosporales, and the class Peronosporomycetes [10]. During the vegetative period of grapevine development, P. viticola completes its life cycle, which is governed by oospores and sporangia. In early spring, zoospores released from macrosporangia, formed by the germination of oospores, are dispersed by rain and wind onto new leaves and shoots, eventually reaching the grape clusters. New zoospores are produced through asexual reproduction, continuously infecting fresh tissues throughout the growing season [11]. Moreover, evidence shows that the survival of the inoculum in plant debris allows it to germinate in successive crops, complicating the eradication of the disease [12]. All grapevine varieties are susceptible to this disease, although the degree of susceptibility varies among them [13,14]. However, genetic diversity analysis has revealed distinct patterns between populations in different geographical regions, highlighting the influence of historical introductions and local environmental conditions [15].
The traditional and most effective method for controlling downy mildew is the periodic application of copper-based formulations, although other types of phytosanitary products, operating either on contact or systemically, have been developed [16]. However, the European Union has established restrictions on the prolonged use of these phytosanitary products due to their potential to promote the emergence of pathogen-resistant strains [6], as well as their negative impact on soil and water quality, which can ultimately affect human health [17,18,19]. There is therefore an increasing need for research into the alternative management of cryptogamic diseases that minimizes the use of these products [20]. Cultivation practices, such as planting grapevines in open, well-ventilated layouts rather than compact ones; managing cover vegetation; employing specific pruning techniques; and ensuring the appropriate handling of pruning residues, represent some alternatives for disease prevention [21,22].
Given that P. viticola sporangia are the main focus for monitoring infection, aerobiological studies that continuously detect their presence and correlate it with meteorological variables are a useful tool for detecting and reducing the spread of the disease [23,24]. Various studies in Spain have described these relationships; however, they differ between years and regions. There are wine-making regions where studies on the detection of P. viticola sporangia in the air are limited, such as the region of the Rías Baixas [13,25,26,27]. The aim of this study was to evaluate the influence of meteorological variables on the aerial concentration of Plasmopara viticola sporangia in two different bioclimatic regions of northwest Spain during the grapevine vegetative cycle.

2. Materials and Methods

2.1. Location and Climatic Characteristics of the Study Area

The study was conducted in three vineyards in northwestern Spain: Areeiro (42°24′13″ N, 8°40′18″ W), Alongos (42°20′03″ N, 7°57′48″ W), and Cenlle (42°18′56″ N, 8°06′03″ W) (Figure 1). This region is strongly influenced by maritime conditions, which diminish as one heads inland toward the east and the distance from the coast increases [28].
Areeiro is located in the Rías Baixas region and biogeographically belongs to the Eurosiberian region. Many of the vineyards are situated close to the coast, creating a microclimate with high humidity, mild temperatures, and frequent rainfall. The traditional cultivation system is in elevated training trellises, structures that lift the vines off the ground to prevent diseases induced by humidity. These systems also provide optimal sun exposure and ventilation. The climate is Atlantic oceanic, with mild winters and precipitation throughout the year, falling to a minimum in the summer [29].
Alongos and Cenlle are located in O Ribeiro, Ourense Province, in the Miño River basin, a region characterized by rugged terrain with fertile valleys and gentle hills. Biogeographically, their location is in a transitional zone between the Eurosiberian and Mediterranean regions [30]. The landscape is dominated by vineyards extending across terraced slopes, utilizing traditional cultivation systems that maximize the use of the hilly terrain and optimize solar exposure. The climate is oceanic with a Mediterranean influence, with mild, wet winters and warmer, drier summers compared to the coastal areas [28].

2.2. Phenological and Aerobiological Study

This study was carried out during the active grapevine growing seasons in 2023 and 2024, focusing on phenological research and sampling P. viticola sporangia in the vineyards using aerobiological methods.
For the phenological study, the most characteristic grapevine varieties of each wine-producing region were selected: Albariño in Areeiro and Treixadura in Cenlle and Alongos. The Biologische Bundesanstalt, Bundessortenamt und Chemische Industrie (BBCH) scale proposed by Meier [31] was followed. In each vineyard, 20 plants were selected to monitor six phenological stages (PS): PS 0 (bud development), PS 1 (leaf development), PS 5 (inflorescence emergence), PS 6 (flowering), PS 7 (development of fruit), and PS 8 (ripening of berries). To determine these stages, weekly visits were made to each vineyard, with two visits per week during the flowering stage (PS 6). The start date of each phenological stage was recorded as the date when 50% of the studied plants were observed in that stage.
Fungal propagule samples were collected using Lanzoni VPPS-2000 model volumetric collectors (Lanzoni Manufacturing, Bologna, Italy) [32], placed 2 m above ground level to avoid obstruction by vine growth. The samplers were calibrated to a flow rate of 10 L/min. For sample processing, the authors applied the Spanish Aerobiological Network protocol [33]. Air samples were trapped in a cylindrical drum covered with Melinex tape previously coated with a 2% silicone solution. In the laboratory, this tape was divided into seven sections, and microscope slides were prepared using glycerinated gelatin with 1% basic fuchsin as the preparation medium. Aerobiological preparations were analyzed under a light optical microscope (OLYMPUS BX50F, Tokyo, Japan) at 400× magnification. P. viticola sporangia were identified as hyaline, ovoid structures, wider at the apex, with lengths ranging from 17 to 40 μm and thicknesses from 10 to 20 μm. The results were expressed as daily sporangium concentration per cubic meter of air (sporangia/m3) using the terminology proposed by Galán et al. [34].

2.3. Meteorological Data

The meteorological data used in this study were recorded by a HOBO meteorological station (ONSET HOBO USB Micro Station Data Logger) located at each vineyard. The daily meteorological variables recorded were average temperature (AvgT, °C), maximum temperature (MaxT, °C), minimum temperature (MinT, °C), relative humidity (RH, %), and dew point (Dp, °C). Precipitation (Rain, L/m2) and wind speed (Ws, km/h) data were obtained from the nearest meteorological stations in the MeteoGalicia network (http://www.meteogalicia.gal/, accessed on 28/11/2024).
To classify the regions where the vineyards are located (Rías Baixas and O Ribeiro), the Currey continentality index [35] was used. This index is calculated based on thermal amplitude and latitude:
Kcu = Am/(1 + (ϕ/3))
where:
  • Kcu = Currey index;
  • Am = thermal amplitude;
  • ϕ = latitude.

2.4. Statistical Analysis

To evaluate the degree of association between meteorological variables and the concentrations of P. viticola sporangia up to 7 days prior, the non-parametric Spearman correlation test was performed. Three periods were considered for the analysis: the 2023 season, the 2024 season, and both seasons combined. The significance levels for the confidence intervals were set at 95% (p < 0.05) and 99% (p < 0.01).
Additionally, a Principal Component Analysis (PCA) was conducted to identify differences in sporangium concentrations between bioclimatic regions and to analyze the influence of all variables on sporangium concentrations in each area. Statistical analyses were performed using IBM SPSS Statistics 24 software.

3. Results

3.1. Grapevine Phenology Cycle and P. viticola Concentrations

The duration of the grapevine growing cycle in all vineyards was similar in both years, with an average duration of 170 days, the exception being Alongos in 2023, where it was shorter, lasting 142 days. Considering both growing seasons, the average duration was longer in Cenlle (177 days) and Areeiro (175 days) than in Alongos (159 days). In 2024 (179 days), the growing cycle was longer than in 2023 (161 days) in all three vineyards (Table 1).
The duration of the phenological stages showed variations across all locations and years (Table 2). In all study vineyards, the longest phenological stage was fruit development (PS 7), lasting 74 days in Areeiro, 72 days in Alongos, and 68 days in Cenlle. The next longest stage was the ripening of berries (PS 8), which lasted 64 days in Areeiro, 51 days in Alongos, and 60 days in Cenlle, using the average value for both growing seasons.
The P. viticola total concentration showed notable differences between the different vineyards and sampling years. In 2023, Areeiro yielded 53,447 sporangia/m3, whereas Alongos yielded 2483 sporangia/m3 and Cenlle 1581 sporangia/m3 (Table 2). In 2024, there was a considerable decrease compared to the previous year, with a 37% reduction at Areeiro, 47% at Alongos, and 71% at Cenlle (Table 2).
In terms of temporal distribution, P. viticola sporangia were recorded at all phenological stages in both years and all vineyards (Table 2 and Figure 2). The highest concentrations in Areeiro were recorded during the flowering (PS 6) and fruit development (PS 7) stages in 2023. However, in 2024, peaks were observed during the fruit development stage and the ripening of berries (PS 7 and 8, respectively). In Alongos and Cenlle, in both growing seasons, the highest concentration of sporangia was observed during the fruit development stage (PS 7). In general, the days with the highest concentration of P. viticola sporangia in the three vineyards were mainly recorded during the fruit development and ripening stages (PS 7, PS 8).
In 2023 in Areeiro, several daily peaks were recorded: 7 June (1045 sporangia/m3), 13 June (1474 sporangia/m3), and 7 and 24 July (1193 and 1454 sporangia/m3), all during the fruit development stage (PS 7). Additionally, between 28 May and 1 June, 17,303 sporangia/m3 were recorded, representing 33% of the total annual count in just five days. However, the maximum peak in Areeiro occurred during the flowering stage (PS 6) on 29 May 2023, with 5604 sporangia/m3. In 2024, in the same vineyard, several days with values over 1000 sporangia/m3 were also recorded during both PS 7 and PS 8.
In the Alongos vineyard, the maximum daily concentrations were lower, with notable peaks of 455 sporangia/m3 on 23 June 2023 and 117 sporangia/m3 on 9 July 2024, both during the fruit development stage (PS 7).

3.2. Meteorological Parameters During the Study

The meteorological conditions in the three vineyards showed marked location-related differences. The continentality index for Areeiro (Kcu = 0.43) classifies this area as ultra-oceanic due to its lower thermal amplitude. The inland area, where Alongos and Cenlle are located, is classified as subcontinental, with Kcu values of 1.5177 and 1.6511, respectively.
Analysis of the meteorological data showed that the average and minimum temperatures did not exhibit significant differences among the three locations over the study period. However, the maximum temperature varied between 26 and 27 °C in Alongos and Cenlle, while in Areeiro, it ranged between 23 and 24 °C (Table 3). On the other hand, all climatic variables contributing to ambient humidity were higher in Areeiro compared to the other two vineyards. The average precipitation over both years was 475 L/m2 in Areeiro, compared to 247 L/m2 in Alongos and 321 L/m2 in Cenlle. Similarly, the average relative humidity was 83% in Areeiro, in contrast to 70% in Alongos and 75% in Cenlle. In terms of the average dew point, Areeiro recorded 14 °C, while Alongos and Cenlle were approximately 1 degree lower. Wind speed was also higher in Areeiro compared to that in Alongos and Cenlle (3.7 km/h in Areeiro vs. <1 km/h in Alongos and Cenlle). When comparing both growing seasons, 2023 was slightly warmer and less rainy than 2024 in all three vineyards (Table 3).
Analysis of the meteorological data averaged by phenological stage (Table S1) reveals that the highest average temperatures occurred during the summer months (PS 8), ranging from 19.98 °C in Areeiro to 23.81 °C in Alongos, in both cases during the 2024 growing season. The lowest minimum temperature values were recorded during the leaf development stage (PS 1), ranging from 5.23 °C in Alongos to 8.52 °C in Areeiro in 2023. As far as rainfall is concerned, in 2023, all three vineyards recorded the highest precipitation during the fruit development stage (PS 7), with values over 100 L/m2. In 2024, precipitation was higher during the bud development stage (PS 0), with 79.73 L/m2 in Alongos and more than 100 L/m2 in Areeiro and Cenlle.

3.3. Meteorological Influence on P. viticola Sporangia

Among the meteorological variables studied, temperature had the greatest influence on the P. viticola sporangium concentration in three vineyards, regardless of the study period (Table 4 and Table S2).
In particular, the average temperature from the seven preceding days in Areeiro (r = 0.626, 2024) and the same-day temperature in Alongos (r = 0.627, in 2023) showed the strongest correlations. Similar r values were also observed for the dew point, with mostly positive correlations. In general, the influence of variables related to water (precipitation and relative humidity) was weaker, showing both positive and negative correlations at different periods. Similar relationships were observed between the detected concentrations and wind speed (Table 4 and Table S2).
Analysis of the correlation results by vineyard revealed that in the ultra-oceanic area (Areeiro), the mean temperature generally exhibited stronger correlations than the maximum or minimum temperatures, with positive correlations in all study periods. Overall, the r value for both the maximum and mean temperatures increased when considering the influence of previous days, reaching its peak seven days before. The temperature on previous days had a greater influence than the temperature on the day of measurement on the P. viticola presence in the air. By contrast, the relationship with the dew point on previous days was weaker than that on the same day. Precipitation showed a negative correlation when analyzing the 2024 data, with r values increasing when considering the influence of previous days. Relative humidity correlated positively with sporangium concentration in 2023. However, in 2024, significant correlations were negative.
In the subcontinental area (Cenlle and Alongos), temperature was also the most influential variable, with correlation results consistently stronger in Alongos than in Cenlle. What was notable about the temperature influence in the transition zone was that it showed a positive correlation in 2023 and a negative one in 2024. After temperature, the dew point and wind speed were the factors exhibiting the highest r values. With regard to wind speed, a similar pattern was observed in both vineyards: a negative influence in 2023 and a positive one in the preceding days in Alongos in 2024. By contrast, relative humidity and precipitation had significantly weaker correlations with the P. viticola sporangium concentration. Relative humidity always showed a positive influence, while rainfall had variable effects.
When the correlations were compared across both seasons (2023 and 2024), a general trend toward a decrease in the significance and strength of the correlations with meteorological factors became evident. In the ultra-oceanic area, correlations with temperature and dew point (both on the same day and up to seven before days) remained significant and positive. Relative humidity and precipitation on the same day and previous days showed less influence when combining seasons than when the years were analyzed separately. In the vineyards in the subcontinental area, maximum temperature only showed significant correlations with sporangia on the same day. Taking the dataset for each location separately, in Alongos, most correlations were positive and significant, with minimum temperature, mean temperature, and dew point maintaining their significance, although with lower r values. However, in Cenlle, for these same variables, correlations were only present on the same day and the preceding day, and for dew point, for the two preceding days. Relative humidity lost its strength when both years were considered together, although the correlation remained positive. With regard to leaf humidity, significant correlations were only found in Areeiro one and seven days before. Wind speed from four and seven days prior had a positive influence in Areeiro, while in Cenlle, it had a negative influence across all the evaluated days.

3.4. Principal Component Analysis

To determine the relationship between the concentrations of P. viticola sporangia recorded in the three vineyards, a principal component analysis was conducted. Principal component 1 (PC1) and principal component 2 (PC2) accounted for approximately 74% of the variance in the data. PC1 grouped the sporangium concentrations from the Alongos and Cenlle vineyards, while those from Areeiro were placed in PC2 (Figure 3).
In order to identify the meteorological factors that most influence the variation in P. viticola sporangium concentrations across the different vineyards, three additional PCAs were performed, one for each study area. The PCA for Cenlle grouped the data into three principal components, while the PCA for Areeiro and Alongos grouped the data into two components. In both Areeiro and Alongos, the two components accounted for a similar percentage of the data variance, close to 70%. In contrast, the three components from the Cenlle PCA accounted for 83.3% of the data variance (Figure 4).
With regard to the distribution of meteorological variables in the different principal components, it was observed that the P. viticola concentration in the ultra-oceanic area (Areeiro) was more strongly associated with component 2, which also grouped relative humidity, rain, and wind speed (Figure 4). Meanwhile, the sporangium concentration in Alongos was more closely associated with component 1, where temperature (maximum, minimum, and average), dew point, and wind speed (with a weaker and negative association) were highlighted. Finally, the sporangium concentration in Cenlle and wind speed were grouped in component 3. These results are consistent with the findings from the Spearman correlation analysis when considering both years (2023 and 2024) together.
Finally, when we took into account the grouping of the meteorological variables analyzed with the PCA, it was observed that the maximum, minimum, and average temperatures, as well as the dew point, were grouped in the same component across all three vineyards, always in the component that accounted for the highest variability (Figure 4). Precipitation was found in the second component, both in the ultra-oceanic vineyard and in the subcontinental vineyards. In the latter, relative humidity was grouped with precipitation in all study areas (Figure 4).

4. Discussion

Knowledge of grapevine phenology over several seasons is essential for ascertaining the characteristics of wine-growing regions. This information enables the effective planning of agricultural tasks and the application of phytosanitary products [36,37]. Furthermore, aerobiological studies of these crops help to optimize harvest yields and to improve the quality of the final product [38].
The main factors that influence the vegetative activity of the vine and the development of its various phenological stages are meteorological in nature, although agricultural management also plays a role [39,40]. The average duration of the grapevine cycle in this study is consistent with that in other studies carried out in the northwest Iberian Peninsula [5,26]. The shortest vegetative cycle throughout the study period was observed in 2023 at the Alongos vineyard. This difference was mainly due to a shortening of PS 8 by 11–14 days compared to that in Cenlle and Areeiro. This may have been caused by temperature variations, which are a key factor for grapevine development in temperate regions [25,41]. In this regard, maximum and average temperatures during this stage were higher in Alongos, and other variables related to humidity were lower. This may have influenced earlier ripening, since the heat dries the soil and stops fruit growth [42].
The meteorological conditions in the three vineyards favored the presence and spread of P. viticola sporangia in the air during the vine growth cycle. For downy mildew to develop in vineyards, climatic conditions are crucial in determining the prevalence and severity of the disease [5]. During spring rains, oospores germinate. These oospores (or the zoospores produced) are transported by rain or wind to the lower leaves, where they penetrate with the help of free water and initiate disease. Once the mycelium develops, sporangiophores emerge through the stomata, releasing sporangia that are carried by the wind and rain to other healthy plants [43]. Oospore germination requires soil temperatures around 12–13 °C and moisture, while the conditions for P. viticola sporulation include a minimum temperature of 13 °C, an optimal temperature of 19 °C, relative humidity higher than 95%, and around 4 h of darkness [44]. In both the vineyard located in the ultra-oceanic area (Areeiro) and the two in the subcontinental area (Cenlle and Alongos), the average relative humidity was above 69%, and the average temperature ranged between 17.12 °C and 19.11 °C, conditions propitious to the presence of the pathogen. However, the sporangium concentration was significantly higher in Areeiro, which distinguishes this vineyard from the others based on the PCA results. This variation may be attributable to the higher average values of relative humidity, accumulated rainfall, and wind speed in Areeiro. Furthermore, the Albariño variety cultivated in Areeiro is more susceptible to downy mildew than the Treixadura variety found in Cenlle and Alongos. Boso et al. [45] conducted a study where they confirmed that the Albariño variety grown in Rías Baixas is more susceptible than the Treixadura variety from O Ribeiro. This could be due to Albariño’s compact bunches, which can retain moisture and hinder ventilation, while Treixadura bunches are looser.
In Areeiro, the peaks of P. viticola sporangium concentration took place during flowering in 2023 and during the ripening of berries in 2024, coinciding with the most critical stages for the development of downy mildew [46]. In this same vineyard, where the highest sporangium concentration in the entire study was recorded (29 May 2023, during GS6), rainfall, daily relative humidity above 85%, and daily average temperatures ranging between 15.99 °C and 17.47 °C were recorded over the three preceding days. The secondary peaks were also characterized by rainfall in the preceding days and daily average temperatures above 18.00 °C, although relative humidity was slightly lower (around 77%). In Alongos and Cenlle, both the maximum concentration peak and the secondary peaks occurred during stage 7 (development of fruit) in both years. In all cases, there were episodes of rainfall, daily relative humidity above 65%, and daily average temperatures exceeding 17.00 °C. These meteorological conditions may have favored the sporulation and viability of the sporangia and thus the increase in their concentrations in the air [47]. In fact, the viability of these asexual propagules is a critical biological and epidemiological trait influencing the development and spread of the disease [48].
Meanwhile, a comparison of concentrations between years shows that although the accumulated rainfall and average relative humidity were generally lower in 2023 than in 2024, the slight increases in temperature (maximum, minimum, and average) in 2023 might have positively influenced the presence of P. viticola sporangia in the air. Indeed, the correlations demonstrated that temperature was the meteorological variable that most influenced the sporangium concentrations in the vineyards, especially in Alongos and Cenlle, when analyzing the influence of all variables in the PCA. These findings are consistent with those reported by [26] in the O Ribeiro wine-growing region of northwestern Spain, where variations in the positivity/negativity of correlation were also observed between different study years. For this same region, Bracero et al. [49] demonstrated that the temperatures on preceding days have a greater influence on sporangium concentrations in the air than those on the day of sampling. This finding acts as an aid for the timely prediction of infection in plants, allowing for the efficient use of phytosanitary products.
Among the variables related to humidity, dew point had one of the strongest influences on P. viticola sporangium concentration, both in the Spearman correlation analysis and in the PCA for the three vineyards. This aligns with results from other studies in the southern Iberian Peninsula [49]. The positive relationship is due to the fact that dew point generates the necessary humidity on the leaf for zoospores to penetrate the stomata and simultaneously promotes the release of sporangia from the sporangium stalks [50]. This humidity can also be generated by rainfall and the relative humidity on previous days, which generally correlated positively in this study. In Areeiro, the bioclimatic area with the highest average relative humidity values, the PCA revealed that this variable was the one most contributing to sporangium concentrations. In this regard, other authors have pointed out that sporangia are only released during rainfall, which is why they are abundant during these periods [5,51]. By contrast, same-day rainfall decreased sporangium concentrations due to the effect of atmospheric washout [52]. This same effect may explain the negative correlations with both variables in the ultra-oceanic area, where rainfall is more frequent.
Wind speed was not always correlated with the sporangium presence, nor in the same way. In other studies in northwestern Spain, it has been shown that no correlation exists between these variables over the course of the preceding days, although when a correlation is detected, it is positive [5,27]. The PCA confirmed that wind speed played an important role in the dispersion and detection of sporangia in all the vineyards. Cortiñas et al. [26] found that both variables were present in the same component but in opposite directions. Wind disturbance, while aiding in the dispersion of propagules, also promotes mixing and dilution, which may be a likely cause for the inverse relationship in the years when it was detected [53].
The detection of airborne P. viticola sporangia is valuable for identifying infection events. Information about the presence of sporangia, combined with an understanding of the meteorological factors that promote their development and, therefore, the spread of the disease, is essential, as it facilitates disease control. In fact, controlling the disease requires a significant amount of plant protection products [54]. Copper compounds, which are commonly used in the vineyards examined in this study to combat the spread of P. viticola, are also widely employed in viticulture to reduce sporangium concentrations to acceptable levels [44]. These treatments help to control the spread of the pathogen, thereby minimizing crop damage. Although numerous alternatives to copper-based treatments have been investigated to control P. viticola, the issue remains unresolved [55], and copper continues to be one of the most commonly used treatments against downy mildew, despite its environmental impacts due to soil accumulation [56]. However, the use of these products could be reduced by combining aerobiological techniques with phenological studies, enabling the more efficient and precise application of plant protection products [26,27,38].
This is a preliminary study, and more years of research are needed to develop predictive models for sporangium concentrations that would allow for the development of an early warning system. With additional data, more reliable results can be achieved, enabling the adaptation of predictive models to specific bioclimatic zones. This would facilitate early decision-making based on weather forecasts, leading to more effective and sustainable disease management. Consequently, the overall chemical treatment load can be reduced and the environmental impact minimized.

5. Conclusions

Grapevine diseases, such as downy mildew, can diminish or even destroy the harvest of a season, especially in regions where the climatic conditions are favorable for the development of these diseases. The present aerobiological study of P. viticola sporangia emphasizes the significance of climatic conditions in vineyards in the northwest of Spain, particularly the role of temperature and rainfall in the days preceding sporangium detection. These factors had a slight but distinct impact on the spread of downy mildew in the two studied bioclimatic zones.
Furthermore, the use of aerobiological samplers that allow for the detection of sporangium concentration, which causes fungal diseases in the vine, is very helpful for implementing an effective integrated pest management strategy. This enables the early detection of the disease, providing enough time for prompt intervention to halt the development of the disease and, therefore, its undesirable effects on the final production.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/horticulturae11030228/s1, Table S1: Main meteorological parameters (MaxT—maximum temperature, MinT—minimum temperature, AvgT—average temperature, Dp—dew point, Rain—rainfall, RH—relative humidity, and Ws—wind speed) averaged by phenological stage (PS 0—bud development, PS 1—leaf development, PS 5—inflorescence emergence, PS 6—flowering, PS 7—development of fruit, and PS 8—ripening of berries) for the studied grapevine seasons (2023 and 2024); Table S2: Spearman correlation test results comparing Plasmopara viticola concentrations (sporangia/m3) to recorded meteorological variables (MaxT—maximum, MinT—minimum, and AvgT—average temperature (°C), Rain—rainfall (mm), Ws—wind speed (km/h), RH—relative humidity (%), and Dp—dew point (°C)) (significance level: p < 0.01 **, p < 0.05 *).

Author Contributions

Conceptualization, M.F.-G. and F.J.R.-R.; methodology, M.F.-G. and M.J.A.; formal analysis, L.C., M.F.-G., M.J.A., K.C.S.E., R.P.O. and F.J.R.-R.; investigation, L.C., K.C.S.E. and R.P.O.; data curation, L.C. and M.F.-G.; writing—original draft preparation, L.C.; writing—review and editing, L.C., M.F.-G., M.J.A., K.C.S.E., R.P.O. and F.J.R.-R.; visualization, L.C. and M.F.-G.; supervision, M.F.-G., M.J.A. and F.J.R.-R.; funding acquisition, F.J.R.-R. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Data Availability Statement

The raw data supporting the conclusions of this article will be made available by the authors on request.

Acknowledgments

Lucía Carrera received a Predoctoral Grant PRE2021-098872, financed by the Ministry of Science and Innovation. Kenia C. Sánchez Espinosa is a beneficiary of the Predoctoral Grant PREUVIGO-23 from the University of Vigo, Spain. This work was supported by the Project “Sustainability of vineyard production: decrease of external inputs, enhance soil biodiversity and increase crop performance” (reference: PID2020-116764RB-I00). The Xunta de Galicia (Spain) provided financial support through recognition as a Competitive Reference Group (ED431C 2023/19, GI-1809 BIOAPLIC), and GISA/BV2 research group.

Conflicts of Interest

The authors declare no conflicts of interest.

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Horticulturae 11 00228 g001
Figure 1. Location of the study vineyards: Areeiro, Alongos, and Cenlle.
Figure 1. Location of the study vineyards: Areeiro, Alongos, and Cenlle.
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Figure 2. Phenology (upper lines: PS 0—bud development, PS 1—leaf development, PS 5—inflorescence emergence, PS 6—flowering, PS 7—development of fruit, and PS 8—ripening of berries), Plasmopara viticola daily concentrations (gray area), average temperature (lines), and rainfall (bars) during the years of study. In order to facilitate the comprehension of the graphics, Plasmopara viticola sporangium concentrations were divided by three in the 2023 graphs. (a) Areeiro 2023–2024, (b) Alongos 2023–2024, and (c) Cenlle 2023–2024.
Figure 2. Phenology (upper lines: PS 0—bud development, PS 1—leaf development, PS 5—inflorescence emergence, PS 6—flowering, PS 7—development of fruit, and PS 8—ripening of berries), Plasmopara viticola daily concentrations (gray area), average temperature (lines), and rainfall (bars) during the years of study. In order to facilitate the comprehension of the graphics, Plasmopara viticola sporangium concentrations were divided by three in the 2023 graphs. (a) Areeiro 2023–2024, (b) Alongos 2023–2024, and (c) Cenlle 2023–2024.
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Figure 3. Results of the principal component analysis applied to Plasmopara viticola concentrations in the vineyards of Areeiro, Alongos, and Cenlle. Factor 1 = Principal Component 1; Factor 2 = Principal Component 2.
Figure 3. Results of the principal component analysis applied to Plasmopara viticola concentrations in the vineyards of Areeiro, Alongos, and Cenlle. Factor 1 = Principal Component 1; Factor 2 = Principal Component 2.
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Figure 4. Principal component analysis (PCA) results for the three locations: Areeiro, Alongos, and Cenlle. Factor 1 = PC 1, Factor 2 = PC 2, and Factor 3 = PC 3. MaxT—maximum temperature, MinT—minimum temperature, AvgT—average temperature, Dp—dew point, Rain—rainfall, RH—relative humidity, and Ws—wind speed.
Figure 4. Principal component analysis (PCA) results for the three locations: Areeiro, Alongos, and Cenlle. Factor 1 = PC 1, Factor 2 = PC 2, and Factor 3 = PC 3. MaxT—maximum temperature, MinT—minimum temperature, AvgT—average temperature, Dp—dew point, Rain—rainfall, RH—relative humidity, and Ws—wind speed.
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Table 1. Dates and duration of the phenological study.
Table 1. Dates and duration of the phenological study.
Study Period
VineyardAreeiroAlongosCenlle
Start date 202324 March28 March14 March
Duration (days)167142173
Harvest7 September17 August3 September
Start date 202413 March19 March12 March
Duration (days)182168181
Harvest11 September3 September9 September
Table 2. Start date of the phenological stages (PS 0—bud development, PS 1—leaf development, PS 5—inflorescence emergence, PS 6—flowering, PS 7—development of fruit, and PS 8—ripening of berries) in the three vineyards in 2023 and 2024, the sum of Plasmopara viticola daily concentrations (SSIn, sporangia/m3) over each phenological stage, the peak maximum daily concentration (Peak, sporangia/m3), and the total sporangium concentration in each study period (Total, sporangia).
Table 2. Start date of the phenological stages (PS 0—bud development, PS 1—leaf development, PS 5—inflorescence emergence, PS 6—flowering, PS 7—development of fruit, and PS 8—ripening of berries) in the three vineyards in 2023 and 2024, the sum of Plasmopara viticola daily concentrations (SSIn, sporangia/m3) over each phenological stage, the peak maximum daily concentration (Peak, sporangia/m3), and the total sporangium concentration in each study period (Total, sporangia).
20232024
Start DateSSInPeakStart DateSSInPeak
Areeiro
PS 024 March14513 March215
PS 12 April3042 April5723
PS 519 April101320517 April1149484
PS 618 May20,925560428 May3811629
PS 77 June22,002147410 June13,3331158
PS 826 July9463102830 July15,2411402
Total 53,447 33,612
Alongos
PS 028 March141313 March8525
PS 13 April31531 March16643
PS 516 April85915 April20522
PS 613 May11426 May8311
PS 730 May18544557 June587117
PS 819 July4906721 July19656
Total 2483 1321
Cenlle
PS 014 March1092212 March12018
PS 15 April110485 April8916
PS 522 April1682320 April575
PS 620 May23531 May395
PS 77 June80811013 June11022
PS 825 July3648323 July485
Total 1581 462
Table 3. Meteorological variables (MaxT °C—maximum temperature, MinT °C—minimum temperature, AvgT °C—mean temperature, RH %—relative humidity, Dp °C—dew point, and Ws Km/h—wind speed) and total precipitation (Rain—L/m2) in the three vineyards (2023 and 2024).
Table 3. Meteorological variables (MaxT °C—maximum temperature, MinT °C—minimum temperature, AvgT °C—mean temperature, RH %—relative humidity, Dp °C—dew point, and Ws Km/h—wind speed) and total precipitation (Rain—L/m2) in the three vineyards (2023 and 2024).
MaxTMinTAvgTRHDpWsRain
Areeiro202323.8713.3918.0783.5314.433.55360.60
202423.1012.4317.1283.1913.413.82589.80
Alongos202327.5011.8619.1169.2212.470.54204.20
202426.8811.7618.6071.3712.520.68290.20
Cenlle202326.2012.1618.3574.5012.951.05255.00
202426.0611.6217.8475.2712.662.30321.30
Table 4. Spearman correlation test results comparing Plasmopara viticola concentration (sporangia/m3) and the meteorological variables recorded (MaxT—maximum, MinT—minimum, and AvgT—average temperature (°C); Rain—rainfall (mm), Ws—wind speed (km/h); RH—relative humidity (%); and Dp—dew point (°C)) (signification level: p < 0.01 **, p < 0.05 *). Only the values of the correlations with the highest r values for each variable are shown.
Table 4. Spearman correlation test results comparing Plasmopara viticola concentration (sporangia/m3) and the meteorological variables recorded (MaxT—maximum, MinT—minimum, and AvgT—average temperature (°C); Rain—rainfall (mm), Ws—wind speed (km/h); RH—relative humidity (%); and Dp—dew point (°C)) (signification level: p < 0.01 **, p < 0.05 *). Only the values of the correlations with the highest r values for each variable are shown.
AreeiroAlongosCenlle
202320242023202420232024
MaxT0.433 **0.498 **0.467 **−0.277 **0.289 **−0.229 **
MaxT_5MaxT_7MaxTMaxT_3MaxTMaxT_5
MinT0.604 **0.618 **0.544 **−0.250 **0.288 **−0.199 *
MinT_1MinT_7MinT_7MinT_7MinT_1MinT_3
AvgT0.559 **0.626 **0.627 **−0.278 **0.347 **−0.222 **
AvgT_4AvgT_7AvgTAvgT_3AvgTAvgT_5
Rain −0.318 **−0.224 **0.249 **−0.203 **0.202 *
Rain_7RainRain_2RainRain_7
RH0.314 **−0.158 *0.194 *0.243 **0.200 **0.222 **
RH_1RH_3RH_7RH_1RH_1RH_7
Dp0.677 **0.632 **0.603 **−0.243 **0.361 **−0.170 *
Dp_1Dp_7Dp_7Dp_3Dp_1Dp_3
Ws−0.192 *0.243 **−0.396 **0.216 **−0.308 **
Ws_1Ws_4Ws_7Ws_5Ws_1
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Carrera, L.; Fernández-González, M.; Aira, M.J.; Espinosa, K.C.S.; Otero, R.P.; Rodríguez-Rajo, F.J. Airborne Plasmopara viticola Sporangia: A Study of Vineyards in Two Bioclimatic Regions of Northwestern Spain. Horticulturae 2025, 11, 228. https://doi.org/10.3390/horticulturae11030228

AMA Style

Carrera L, Fernández-González M, Aira MJ, Espinosa KCS, Otero RP, Rodríguez-Rajo FJ. Airborne Plasmopara viticola Sporangia: A Study of Vineyards in Two Bioclimatic Regions of Northwestern Spain. Horticulturae. 2025; 11(3):228. https://doi.org/10.3390/horticulturae11030228

Chicago/Turabian Style

Carrera, Lucía, María Fernández-González, María Jesús Aira, Kenia C. Sánchez Espinosa, Rosa Pérez Otero, and Francisco Javier Rodríguez-Rajo. 2025. "Airborne Plasmopara viticola Sporangia: A Study of Vineyards in Two Bioclimatic Regions of Northwestern Spain" Horticulturae 11, no. 3: 228. https://doi.org/10.3390/horticulturae11030228

APA Style

Carrera, L., Fernández-González, M., Aira, M. J., Espinosa, K. C. S., Otero, R. P., & Rodríguez-Rajo, F. J. (2025). Airborne Plasmopara viticola Sporangia: A Study of Vineyards in Two Bioclimatic Regions of Northwestern Spain. Horticulturae, 11(3), 228. https://doi.org/10.3390/horticulturae11030228

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