Grape-producing Regions Research Articles

Generating surface soil moisture at the 30 m resolution in grape-growing areas based on stacked ensemble learning

ABSTRACT Accurate and timely monitoring of drought conditions in grape-producing regions is crucial for achieving healthy growth of grapes. Current soil moisture (SM) products are primarily available at coarse resolutions (e.g. several to tens of kilometres), constraining its applications at fine scales. Here, we trained a weighted stacking ensemble model including three tree-based models (categorical boosting, random forest, and gradient boosting decision tree), using seven forcing parameters related to spectral reflectance (SR), land surface temperature (LST), and evapotranspiration (ET), in conjunction with the digital elevation model (DEM) feature. The weighted stacking ensemble model exhibited an average R2 of 0.86 and an average RMSE of 0.021 m3/m3 in simulating SM in the vegetive stage and the mid-ripening stage of grape. Then we generated high spatiotemporal downscaled SM (HSM) data at a grape growing area at high spatiotemporal resolutions (30 m, 8-day) from 2009 to 2018. Our HSM dataset demonstrated strong spatial, seasonal and interannual dynamics that align with 500 m SM dataset derived from single MODIS data, and the HSM dataset shows more details in SM distribution. Additionally, the SM time series in the HSM is consistently correlated with drought events, offering intricate spatiotemporal information for drought monitoring. The application of downscaled SM results identified a concentration of drought events in the eastern foothills of the Helan Mountains, particularly severe drought conditions were observed in the Hongsipu production area. Drought occurrences in the Hongsipu production area ranged from 90% to 91% during May and June, decreasing to 73% and 41% in July and August, respectively. These findings significantly contribute to enhancing high spatiotemporal SM monitoring capabilities, offering valuable guidance for timely water management in grape-growing regions.

Impact of Vineyard Fallow Practices on Reducing Meloidogyne hapla Population Densities

The northern root-knot nematode (Meloidogyne hapla) is a common plant-parasitic nematode in northern grape production regions. This nematode induces small galls on roots, which restricts water and nutrient uptake, resulting in poor vine establishment or exacerbated decline in stressed vines. A study was conducted to explore the impacts of site management practices on M. hapla population densities following removal of wine grape (Vitis vinifera) vineyards in Washington State. Soil was collected from 38 fields, M. hapla second-stage juvenile densities in soil were determined, and to assist in identifying M. hapla in potentially low-population density samples, an eight week-long tomato (Solanum lycopersicum) bioassay was conducted. Vineyard managers also provided information on site management techniques. Of the 20 total management techniques and combinations explored (e.g., fallow duration, cover crops, mowing, irrigation, herbicide applications), only one component resulted in lower M. hapla population densities: duration of vine-free period. A duration of at least one-year post vineyard removal showed a decline in M. hapla population densities in the sampled former vineyard sites. These results suggest that a fallow period could be useful as a non-chemical management tool for M. hapla in vineyard replant soils. However, consideration of additional site management factors such as weed management, soil series and amendments, interim crop planting, and irrigation or accumulated rainfall that may support M. hapla development is necessary.

Fungicide Use Patterns in Select United States Wine Grape Production Regions.

Wine grape production (Vitis sp.) in the United States requires fungicide inputs for disease control. Currently, there is limited data available on vineyard fungicide use patterns. This information is important in developing tailored recommendations for disease management and fungicide stewardship. In this paper, we summarize the wine grape vineyard fungicide use patterns from four major regions: Napa and Sonoma valleys (California), Willamette Valley (Oregon), Columbia Valley (Washington), and several smaller regions east of the Mississippi River in years 2009 to 2020. We learned that the average in-season total fungicide applications ranged regionally from 5.6 to 8. The most commonly applied Fungicide Resistance Action Committee (FRAC) codes in spray programs were FRAC 3, 13, and M02 across all regions, with some variation to the top four groups in each region. Most applications were made on 14-day intervals; however, shorter intervals (7-day) were favored early season, and longer intervals (21-day) were favored late season. Tank-mixing multiple active ingredients was common east of the Mississippi River during all stages of grape development; this action was typically favored during the bloom period in other regions. In a subset of records that participated in FRAC 11 fungicide resistance testing, the average number of FRAC 11 applications after testing was reduced to either no applications or one application in Napa and Sonoma valleys. This survey provides regionally specific data related to fungicide stewardship practices that could be a focus for future stewardship messaging and fungicide resistance selection training, including total product use (selection events), spray intervals (selection pressure), and tank mixing (selection management).[Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Productivity and Brix value of Green Grapes (Vitis vinifera L var. Muscat Saint Vallier) at Different Location and Pruning Time in Buleleng Bali

Bali is one of the grape-producing regions in Indonesia, and grape cultivation is carried out in the North Bali area of Buleleng Regency. Grape growers in Bali began to plant other grape varieties, namely green grapes (Vitis vinifera L. var. Muscat Saint Vallier). This grape variety originates from France and grows successfully in the tropics. Currently, there needs to be more information about the yield potential and quality of green grape varieties. This study aims to determine the productivity and quality of green grapes at several harvest periods and locations. The research was conducted from January 2021 to September 2022 at three sub-district locations: Gerokgak, Kalisada, and Seririt. The research was conducted at six locations, namely Gerokgak 1, Gerokgak 2, Gerokgak 3, Kalisada 1, Kalisada 2, and Seririt. Data collection was carried out during three pruning to harvest periods: January–March, April–June, and July–September. Harvest period and planting location show a significant influence on green grape productivity. Observations on grape productivity in different years showed no significant results, and there was no interaction between location and harvest period. The harvest period for two consecutive years shows that the July–September harvest period gives the best yields. The quality of the yield of green grapes shown in the fruit obrix at both locations at different harvest periods shows that the obrix of this variety remains the same.

Predatory Phytoseiidae mites (Acari: Mesostigmata) in vineyards of northern Portugal

Phytoseiids are important biological control agents on different cultivated plants. This work aimed to know the diversity of phytoseiids and compare the abundance and richness of these mites found in grape-producing regions located in northern Portugal. Samplings were conducted in the subregions of Ave, Cávado, Douro, Lima and Minho Rivers between July and September 2017, in 25 vineyards (three in Ave, four in Cávado, eight in Douro, five in Lima and five in Minho Rivers), by collecting 50 leaves/vineyard. A total of 4,372 phytoseiid mites were found, and the highest abundance of phytoseiids per leaf was in Lima, with an average of 6.4, followed by Douro and Minho, with 2.5 and Ave, with 2.0. The highest richness was found in Ave and Douro, with 80% of the species reported. Typhlodromus pyri predominated in nearly all rivers, except when comparing Ave versus Douro, Cávado versus Douro and, Cávado versus Minho; in these cases, Kampimodromus aberrans predominated in Douro and Minho. This also occurred when K. aberrans and Typhlodromus exhilaratus were compared between Douro and Minho. Comparing Ave and Minho, T. exhilaratus predominated in Minho. Knowing about the phytoseiids present in the studied regions of northern Portugal helps develop biological control strategies and balance these agroecosystems.

Effects of mesoclimate and microclimate variations mediated by high altitude and row orientation on sucrose metabolism and anthocyanin synthesis in grape berries

Climate change and extreme weather pose significant challenges to the traditional viticulture regions. Emerging high-altitude grape-producing regions with diverse orientations have shown great potential in coping with this challenge. Stable, high-quality wine grape production may be achieved by synchronizing the meso- and microclimate. To clarify the role of high altitude and row orientation in meso- and microclimate and the response of berries to it, we evaluated seven years (2012–2018) of climate data, two years of basic grape (Cabernet Sauvignon, Vitis vinifera L.) quality, and one-year microclimate from veraison to harvest. By comparing two locations (Sidon 2 047 m, Sinon 2 208 m) in Yunnan Province, China, we found that the average temperature has been stable at approximately 15 °C for seven years, with no extreme weather or, noticeable global warming. The light intensity (LI) in the north-south (NS) was more balanced than the east-west (EW) direction, and the east-west to the south (EW-S) canopy side was almost higher than the other sides. High LI was associated with high photosynthetically active radiation (PAR), ultraviolet (UV), and infrared (IR) light and vice versa. The north-south to the east (NS-E) and east-west to the north (EW-N) sides were characterized by lower LI and higher UV and IR light, and higher total anthocyanin content. Most anthocyanin synthesis-related genes, for example, VvF3′H and VvF3′5′H, were highly expressed in NS-E from veraison to maturity. Perhaps UV and IR light induced their expression. This study provides new insights on the role of differently orientated rows in controlling grape quality due to varied light quality. The findings are globally significant, particularly in the context of climate change, and offer fresh insights into berry physiological responses and decision-making for the management of existing vineyards.

Site characteristics determine the effectiveness of tillage and cover crops on the net ecosystem carbon balance in California vineyard agroecosystems.

Globally, wine grape vineyards cover approximately 7.4 M ha. The potential for carbon (C) storage in vineyards is of great interest to offset greenhouse gas emissions and mitigate the effects of climate change. Sustainable soil management practices such as cover crop adoption and reduced tillage may contribute to soil organic carbon (SOC) sequestration. However, site-specific factors such as soil texture, other soil physicochemical properties, and climate largely influence the range and rate to which SOC may be stored. To measure the potential for C storage in vineyards under varying sustainable soil management practices, we calculated the net ecosystem carbon balance (NECB) of three cover crops [perennial grass (Poa bulbosa hybrid cv. Oakville Blue); annual grass (barley, Hordeum vulgare); resident vegetation (natural weed population)] under conventional tillage (CT) and no-till (NT) management. Results provided evidence that vineyards served as C sinks. In sandy soils, the type of cover crop and tillage may be of little influence on the NECB. While in finer-textured soils, tillage reduced the NECB and higher biomass-producing cover crops enhanced the overall C storage potential of the vineyard agroecosystem. Overall, our results revealed that site characteristics, namely, soil texture and climate, were key determinants of the C storage potential of vineyards in Mediterranean climates such as those found in coastal and inland California wine grape production regions.

Rain-shelter Cultivation Affects the Accumulation of Volatiles in ‘Shuijing’ Grape Berries during Development

Rain-shelter cultivation could protect grape berries from many diseases and affect grape berry quality. However, there have been few studies of the effects of rain-shelter cultivation on the accumulation of volatiles in Shuijing grapes grown in Yunnan Province. Therefore, the goal of this research was to explore the effects of rain-shelter cultivation on the accumulation of volatiles in Shuijing grape berries during development. The Shuijing grapes used during this study were grown in the Yunnan Province of southwest China in two consecutive vintages (2018 and 2019). The results showed that rain-shelter cultivation promoted grape ripening and inhibited volatiles synthesis in Shuijing grape berries. However, the application of rain shelters did not affect the accumulation patterns of volatiles; instead, it affected the concentrations of volatiles in Shuijing grape berries, especially during the maturation phase [12–15 weeks after flowering (WAF)]. The concentrations of isoprenoid-derived volatiles (2019), fatty acid-derived volatiles, and amino acid-derived benzenoids in Shuijing grape berries were decreased by rain-shelter cultivation during the maturation phase. The concentration of 2,5-dimethyl-4-methoxy-3(2H)-furanone (mesifurane) was also decreased by rain-shelter cultivation during the late maturation phase (14 and 15 WAF). A principal component analysis (PCA) indicated that the vintage had a much greater influence on the physicochemical parameters and volatiles of the Shuijing grape berries than the cultivation method. This work reveals the formation and accumulation patterns of volatiles of Shuijing grape berries under rain-shelter cultivation during development and has significance for exploring the potential of rain-shelter cultivation in grape-producing regions with excessive rainfall.

MOLECULAR CHARACTERIZATION OF BLACK FOOT DISEASE PATHOGENS IN GRAPEVINE NURSERIES AND EVALUATION OF SOME FUNGICIDES FOR CONTROL OF THE MOST VIRULENT ISOLATES

Black foot disease, which is mainly caused by Ilyonectria Chaverri & Salgado and Dactylonectria L. Lombard & Crous species, causes serious destruction in most of the wine and grape producing regions of the world, particularly in nurseries and young vineyards. The aim of this research was to evaluate the present situation of black foot disease in grapevine nurseries (Vitis Vinifera L.), to identify its potential agents at morphological and molecular levels and to develop a control strategy against isolates found as the major virulent ones in pathogenicity tests. This study also represents the first attempt to control black foot disease in grapevine saplings in Turkey. Preliminary surveys were carried out in 21 grapevine nurseries in the Aegean Region during 2019 growing season. Black foot species obtained from vine saplings were identified as Ilyonectria liriodendri (Halleen, Rego & Crous), Dactylonectria macrodidyma (Halleen, Schroers & Crous) and D. torresensis (A. Cabral, Rego & Crous), using morphological and molecular methods. The pathogenicity studies revealed that the most virulent isolates belonged to I. liriodendri. Twelve chemical and one biological fungicides were screened in vitro for mycelial inhibition of I. liriodendri isolates. The experiments were performed in three replicates for each of the chemical fungicides. Sterile distilled water, instead of fungicide solution, was used for control trials. Mixtures of cyprodinil + fludioxonil, thiabendazole + fludioxonil + metalaxyl–m + azoxystrobin and azoxystrobin + metalaxyl-m + fludioxonil were the most effective chemical fungicides tested in mycelial inhibition of I. liriodendri isolates. Chemical fungicides mixtures of boscalid + kresoxim-methyl, promocarb hydrochloride (HCL) + fosetyl-al, azoxystrobin + difenoconazole, fludioxonil + metalaxyl–m and individual fungicides; cyprodinil, fluoxapyroxad, hymexazole, fenhexamid and 8-hydroxyquinoline sulphate were not effective on mycelial inhibition. Biocontrol activity of Trichoderma harzianum Rifai KRL-AG2 strain against I. liriodendri was evaluated. The experiment was performed in four replicates for each isolate. Petri dishes with only I. liriodendri mycelial discs used as controls. Treatment with Trichoderma harzianum Rifai KRL-AG2 strain provided 60.1% to 80.6% inhibition against I. liriodendri isolates. The most effective fungicides tested in vitro were evaluated in 2020 and 2021 under controlled conditions against possible infections of I. liriodendri during the rooting process of 1103 Paulsen grapevine rootstocks. Mixtures of thiabendazol + fludioxonil + metalaxyl–m + azoxystrobin and cyprodinil + fludioxonil were the most effective fungicides in the experiments conducted in 2020 and 2021, followed by azoxystrobin + metalaxyl-m + fludioxonil and Trichoderma harzianum Rifai KRL-AG2 strain.

Characterization of arbuscular mycorrhizal fungal communities associated withvineyards in northwestern Iran

Arbuscular mycorrhizal fungi (AMF) establish beneficial symbiotic associations with plants, enhancing their nutrient uptake, growth, and stress tolerance. The present study was aimed to investigate AMF spore density, species composition, mycorrhizal colonization patterns, and correlation of these indices with soil physicochemical parameters at four vineyards located in one of the most important grape-producing regions of Iran (West Azerbaijan province). Forty-three soil samples were collected from four grapeproducing regions during July-August 2019. The total spore abundance ranged from 39-647 spores per 100 g dry soil. Twelve AMF species, representing six genera (Rhizophagus, Funneliformis, Glomus, Septoglomus, Claroideoglomus, and Scutellospora) were identified. Rhizophagus fasciculatus was the most frequently found species, with a frequency of 75%. Two of the identified species, G. glomerulatum and Scutellospora calospora are new for the mycoflora of Iran. Significant negative correlations were detected between AMF attributes [spore density, AMF colonization frequency (F%) as well as AMF colonization intensity (M%)] and soil phosphorus content. The results provide insights into the AMF communities and dynamics in vineyards as influenced by soil parameters, improving our understanding of soil biological fertility in grape production systems.

Water Footprint of Table Grape Production Systems: A Review of South African and Global Studies

Being a water-scarce country, South Africa (SA) faces several water challenges, including drought and other effects of climate change. Therefore, there is a need to improve water-use efficiency (WUE) by accurately quantifying the water use and WUE of table grape vineyards. The objective of this review is to (i) provide an overview of water footprint (WF) studies conducted on table grape production systems in SA and globally; (ii) identify limitations in current WF assessments of table grape production systems; and (iii) establish a range of WF values for table grape production systems as an indicator of WUE and for use in decision-making regarding sustainable freshwater use. The review has demonstrated that only a limited number of detailed WF studies have been undertaken on table grapes in SA and globally. Region-specific lookup tables for quantifying blue, green and grey water use in table grape production systems are available for three table grape production regions of SA and could be used for future WF assessments. Most global studies conducted on grape WF and WUE were desktop studies and did not include actual field records from production units, nor did they distinguish between different grape types (table, raisin and wine grapes). WF values must be interpreted in context, specifically regarding the water used versus yield, quality and income, as well as the region, climatic conditions, soil characteristics, irrigation and cultivation practices. For future WF and WUE assessments, a more detailed breakdown of water use is recommended, both during the production process and postharvest.

The Bio-Ecology of the Grapevine Leaf Miner, Holocacista capensis (Lepidoptera: Heliozelidae) in the Western Cape, South Africa

The lepidopteran leaf-mining larvae of Holocacista capensis were recorded on the outskirts of Paarl (Western Cape), South Africa, in 2012 for the first time. Thought to have local origins, the moth has been recorded on many grape varieties in South Africa since. In order to develop appropriate management strategies, aimed at maintaining effective control of the pest in commercial vineyards, various aspects of the pests′ ecology must be known. The current study provided morphological characteristics associated with wing and abdominal colouration, which can be used to discern between male and female moths using a stereo microscope. The seasonal cycle of larvae and adults throughout a grapevine growing season was established. The leaf miner was detected in the three grape areas surveyed (Berg River, Hex River and Olifants River). Areas in the grape producing regions of the Western Cape that are heavily impacted by the leaf miner include Paarl, Riebeeck Kasteel, Tulbagh, Piketberg and Wellington. Moth and larval abundances were observed to reach considerably high numbers in February. Live larval abundances decreased from the middle of March, whilst adult abundances were only seen to drop in early April. This study aimed to assist towards the development of appropriate management strategies against the pest.

Actinobacteria Associated with Vineyard Soils of Algeria: Classification, Antifungal Potential Against Grapevine Trunk Pathogens and Plant Growth-Promoting Features

Grapevine trunk diseases(GTDs) are among the most destructive diseases of vineyards worldwide, including Algeria. In the fungal complex involved in GTD symptoms, referred as grapevine trunk-pathogens, Paeomoniella chlamydospora and Phaeoacremonium minimum have a determining infecting role as pioneer fungi. Due to the lack of efficiency of conventional disease management practices, a search for alternative strategies, such as biocontrol, is needed. Taking the approach of looking for biocontrol candidates in the environment surrounding the plant, the present study explored actinobacteria diversity within vineyard soils of six grape-producing regions in Algeria. Based on their 16S rRNA gene sequence, identification and phylogenic analysis were performed on the 40 isolates of actinobacteria obtained. Forty percent of strains were attached to Streptomyces, including two evidenced new species, and 32.5% were affiliated to Saccharothrix. The other less represented genera were Actinoplanes, Nocardia, Nocardiopsis, Lentzea, Nonomuraea, Promicromonospora, Saccharopolyspora and Streptosporangium. Screening based on antagonistic and plant growth promotion (PGP) abilities of the strains showed that 47.5% of the isolates exhibited appreciable antagonistic activities against both Pa. chlamydospora and Pm. minimum, with the two best strains being Streptomyces sp. Ms18 and Streptomyces sp. Sb11. Screening for plant growth promoting properties demonstrated that majority of the strains were able to produce indole acetic acid, siderophores, ammonia, ACC deaminase, cellulase and amylase, and fix N2. Through a PGP-traits-based cluster analysis, the most interesting strains were highlighted. Taking into account both antagonistic and PGP properties, Streptomyces sp Sb11 was selected as the most promising candidate for further evaluations of its efficiency in a GTDs context.

Vineyards in transition: A global assessment of the adaptation needs of grape producing regions under climate change

This paper suggests how climate change may transform vineyards. We consider changes in agro-climatic indicators derived from climatic variables as drivers for adaptation needs. We use two climate scenarios, GCM GFL-ESM2M and HadGEM2-ES, with 0.5° spatial resolution and daily time step forced by two emission scenarios, RCP2.6 and 6.0, to estimate the transition of potential vineyards in the major grape production world areas by the late 21st century. We present and discuss changes in three impact indicators – one drought indicator and two temperature ones – aimed at exploring the benefits of transition-based policies. The drought indicator provides insights to prepare adaptation for extreme events in probabilistic terms. The temperature indicators offer information on the transition towards suitable zones of production. Future projections suggest a lack of water to maintain current levels of production in all regions of the world. Furthermore, thermal suitability of grapevine may be greatly affected in China and the Mediterranean region. Nevertheless, the possibility of quality wines is not altered within the regions with adequate suitability. Lastly, a portfolio of strategies to adapt to the future climate is presented.

Temperature Thresholds and Thermal Requirements for Development and Survival of Dysmicoccus brevipes (Hemiptera: Pseudococcidae) on Table Grapes.

Temperature is an important climate factor that has a direct influence on insect biology and consequently a crucial role in forecasting and integrated pest management. The mealybug Dysmicoccus brevipes (Cockerell) (Hemiptera: Pseudococcidae) is one of the most common species in Brazilian vineyards. Here, development and survival of D. brevipes on leaves of table grapes (Vitis vinifera cv. Itália) were studied at five constant temperatures (15, 20, 25, 28, and 30 ± 1°C) under laboratory conditions. We investigated the developmental time and nymphal survival, temperature thresholds, and the degree-day requirements for each life stage of D. brevipes. The developmental time for the nymphal stage ranged from 32 to 130days with decreasing the temperature, with the temperatures of 28 and 30°C providing the shorter developmental time. Survival of the entire nymphal stage was affected by the temperature, ranging from 81% at 20°C to 1% at 15°C. The predicted upper lethal temperature was 34.5°C, while the optimal temperature was 28.6°C. The minimum threshold for total development of D. brevipes occurred at 8.2°C. Dysmicoccus brevipes required 678.4 degree-days to complete development from first-instar nymph to adult. The temperature of 30°C was the most suitable for the development of D. brevipes. The thermal thresholds estimated for D. brevipes life cycle suggest that this species can develop in different table grape-producing regions of Brazil, in a temperature range between 8 and 35°C.

Vineyard Floor Management and Cluster Thinning Inconsistently Affect ‘Pinot noir’ Crop Load, Berry Composition, and Wine Quality

Growers of high-end ‘Pinot noir’ wine grapes (Vitis vinifera L.) commonly reduce yield by cluster thinning with the goal of increasing fruit quality; however, there are no objectively defined yield targets to achieve optimum fruit composition. Canopy leaf area relative to fruit yield can affect total soluble solids (TSS), and recommendations have been established for warm wine grape production regions. However, the relationship between leaf area and photoassimilation differs among climates and training systems. Leaf area to yield (LA:Y) ratios developed in warm, arid regions may not be suitable for cool, wet regions such as western Oregon. A 3-year field study was conducted to elucidate relationships between canopy to yield ratios and berry composition for ‘Pinot noir’. Vegetative growth and fruit yield were manipulated through competitive cover cropping and cluster thinning. Growth was manipulated in three ways: perennial red fescue (Festuca rubra L.) was grown in 1) both (Grass), 2) one (Alternate), or 3) neither (Tilled) of the alleyways flanking the vine row. Within each vineyard floor treatment, fruit clusters were thinned to one per shoot (Half Crop) or vines were left unthinned (Full Crop). Floor management influenced both canopy size and yield because of altered vine nitrogen (N) status. Effects of crop load on berry components were not always consistent between the crop load metrics used [yield to pruning weight (Y:PW) ratio or LA:Y]. In 2 years, TSS reached a maximum at similar LA:Y; however, this did not necessarily produce optimum TSS. Yield had the greatest influence on pH and total anthocyanins (ACY) in the highest yielding, coolest year. Crop load metrics were not reliable predictors of TSS because of the dominant effect of seasonal variation. Relationships between canopy to yield metrics and other berry components were partially explained by tissue N, photosynthetic photon flux (PPF) through the cluster zone, and/or yield. Cluster thinning to adjust yields may not alter source to sink relationships or canopy to yield ratios enough to overcome ripening limitations in cool climates. Only one wine vintage had sensory differences with Alternate-Half Crop and Alternate-Full Crop wines ranked high quality and Tilled-Half Crop and Tilled-Full Crop wines ranked low quality by both consumer and winemaker panels. Therefore, cluster thinning may have limited impact on wine sensory properties.

Phylogeny of Geminivirus Coat Protein Sequences and Digital PCR Aid in Identifying Spissistilus festinus as a Vector of Grapevine red blotch-associated virus.

Grapevine red blotch-associated virus (GRBaV) is a single-stranded DNA virus, proposed to be a member of the family Geminiviridae, and is associated with grapevines showing red blotch symptoms in North America. The existence of the virus was reported in 2012, and subsequently detected in grapevines in major grape production regions. We investigated if a vector exists that can transmit GRBaV in vineyards. Phylogenetic analysis of the predicted amino acid sequence of coat protein (CP) of GRBaV with the CP of 23 geminiviruses representing all seven genera of the family Geminiviridae revealed that GRBaV-CP was most similar to that of Tomato pseudo-curly top virus, a geminivirus known to be transmitted by a treehopper (Membracidae), a family that is closely related to leafhoppers (Cicadellidae). To identify vectors of GRBaV, hemipteran species within and nearby wine grape vineyards where virus spread was suspected were collected and transmission assays were conducted. Among the species tested, the three-cornered alfalfa hopper Spissistilus festinus (Hemiptera: Membracidae) was able to both acquire the virus from a grapevine infected with GRBaV and transmit the virus to healthy grapevines in the laboratory. In commercial vineyards, lateral shoots of grapevines girdled due to feeding injury by the adult three-cornered alfalfa hopper also tested positive for the virus using digital PCR. These findings represent an important step in understanding the biology of GRBaV and develop management guidelines.

Ferrisia gilli(Hemiptera: Pseudococcidae) Transmits Grapevine Leafroll-Associated Viruses

Several mealybug species are vectors of grapevine leafroll-associated viruses (GLRaV), which cause the economically important grapevine leafroll disease in grape-producing regions worldwide. The mealybug Ferrisia gilli Gullan is a new pest of grapevines in El Dorado County, located in the Sierra Foothill wine-growing region of California. GLRaV species 1, 2, 3, and 4LV have been detected in vineyards with symptomatic vines in the Sierra Foothills. We conducted controlled virus acquisition and transmission experiments using source vine accessions infected with different combinations of GLRaV. We determined that F. gilli acquired GLRaV 1, 2, 3, and 4LV, and transmitted GLRaV-3 and GLRaV-4LV to uninfected recipient vines. Like numerous other mealybug species, in addition to causing direct damage to vines, F. gilli poses a threat to the grape industry as a vector of economically damaging viruses.

Early events of grapevine resistance towards downy mildew by a systems biology approach

Grapevine downy mildew, caused by the fungus Plasmopara viticola (Berk. & Curt.) Berl. & de Toni was introduced in European vineyards in the 1870s and quickly spread to all major grape-producing regions worldwide. The early events of grapevine resistance to P. viticola were accessed using transcriptomic, metabolomic and proteomics approaches in the cultivars, ‘Regent' and ‘Trincadeira', resistant and susceptible to downy mildew, respectively. At the transcript level the resistant genotype ‘Regent' presents signalling and defence-related transcripts up-regulated as soon as 6hpi. At the metabolome level, our results show that ‘Trincadeira' and ‘Regent' are intrinsically different as ‘Regent', the resistant cultivar, is able to activate the phenylpropanoid pathway and to accumulate linolenic acid, the precursor of jasmonate in the octadecanoid cascade. At the proteome level ‘Regent' presents upregulated proteins mainly belonging to the functional categories of photosynthesis, carbohydrate metabolism and defence, indicating that this cultivar makes a more efficient use of light, in CO2 assimilation and obtaining intermediate metabolites from photoassimilates for the biosynthesis of secondary metabolites and subsequent defence responses. Our data brings new insights on the molecular processes underlying resistance to Plasmopara viticola, which may eventually enable the design of novel strategies for pathogen control.

Foliar Reflective Film and Water Deficit Increase Anthocyanin to Soluble Solids Ratio during Berry Ripening in Merlot

Elevated temperatures can decrease the ratio of anthocyanins to soluble solids in red-skinned berries, and warming trends in grape production regions have raised concern about color to alcohol balance in wines produced from fruit with altered ratios. This study investigated the effect of a foliar reflective film on the ratio of anthocyanins to soluble solids in deficit-irrigated Merlot grapevines over a 5-year period. Vines were irrigated to provide 90 or 35% of estimated water demand (DI90 and DI35, respectively) and were either sprayed with a kaolin-based reflective film or left unsprayed using a replicated, split-plot design. During the 2008–2010 seasons, crop load was adjusted in half of the vines within each subplot by removing 50% of clusters prior to bloom. Regardless of crop load, the reflective film increased the ratio of anthocyanins to soluble solids in DI90 and DI35 when the concentration of soluble solids was 18 to 24%. The reflective film did not alleviate the decrease in yield or titratable acidity associated with water deficit, and it had no influence on yield per vine. However, it reduced the number of berries per cluster, especially in DI35-irrigated grapes. In DI90-irrigated vines, decreased berry number per cluster was associated with increased berry fresh weight and anthocyanin content per berry. Cluster removal influenced berry composition at harvest only under DI35 irrigation. The ratio of anthocyanins to soluble solids during ripening was higher in DI35-irrigated plants than in those under DI90 irrigation. Taken together, foliar reflective film combined with deficit irrigation increased the ratio of anthocyanins to soluble solids under arid conditions with high solar radiation.