Kaolin Particle Film Protects Grapevine cv. Cabernet Sauvignon Against Downy Mildew by Forming Particle Film at the Leaf Surface, Directly Acting on Sporangia and Inducing the Defense of the Plant

Downy mildew is a major threat to viticulture, leading to severe yield loss. The use of traditional copper-based fungicides is effective, but has adverse effects on the environment and human health, making it urgent to develop an environmentally friendly disease management program. Multi-functional kaolin particle film (KPF) is promising as an effective and safer treatment strategy, since this material lacks chemically active ingredients. In this study, ability of Kaolin particle film (KPF) pretreatment to protect grapevine leaves from Plasmopara viticola was tested and the mode of action of KPF was analyzed. KPF application reduced the disease severity and the development of intercellular hyphae. Additionally, there was reduced accumulation of H2O2 and malondialdehyde (MDA) with pretreatment. The observation of ultrastructure on the leaf surface showed KPF deposition and stomatal obstruction, indicating that KPF protected plants against disease by preventing the adhesion of pathogens to the leaf surface and blocking invasion through the stomata. KPF pretreatment also activated host defense responses, as evidenced by increased activities of anti-oxidative enzymes [superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT)] and defense-related enzymes [phenylalanine ammonia-lyase (PAL), chitinases, and β-1,3-glucanases], increased phytohormone signals [abscisic acid (ABA), salicylic acid (SA), and jasmonic acid (JA)] and the up-regulation of defense genes related to plant defense. Overall, these results demonstrate that KPF treatment counters grapevine downy mildew by protecting leaves and enhancing plant defense responses.

More Than Just Wine: The Nutritional Benefits of Grapevine Leaves

The domesticated species Vitis vinifera L. harbours many cultivars throughout the world that present distinctive phenology and grape quality. Not only have the grapes been used for human consumption, but the leaves are also used as a source of bioactive compounds and are present in the diets of several Mediterranean countries. We have selected seven different cultivars and performed elemental, fatty acid (FA) and pigment profiling. Total reflection X-ray fluorescence (TXRF) enabled the identification of 21 elements. Among them, Na, Ca and K were highly represented in all the cultivars and Zn was prevalent in V. vinifera cv. ‘Pinot noir’ and ‘Cabernet sauvignon’. Through gas chromatography, six FAs were identified, including omega-3 and omega-6 FA, the most abundant mainly in V. vinifera cv. ‘Tinta barroca’, ‘Pinot noir’ and ‘Cabernet sauvignon’. FA composition was used to determine nutritional quality parameters, namely atherogenic, thrombogenic, hypocholesterolemic/hypercholesterolemic and peroxidisability indexes as well as oxidability and oxidative susceptibility. Grapevine leaves were highlighted as a suitable source of health-promoting lipids. Given the popularity of “green” diets, we have also performed a leaf pigment analysis. Seventeen pigments including chlorophylls, trans-lutein, b-carotene and zeaxanthins were detected. ‘C19′ presented the highest content of most of the detected pigments.

Vineyard Fertilization Management for Iron Deficiency and Chlorosis Prevention on Carbonate Soil

Nitrogen fertilizer efficiency in grapevine production is an important objective for solving the trade-off between improving yield and quality in agroecosystems and reducing environmental impacts. Influence of soil nitrogen fertilization and Fe foliar application on iron dynamics in soil and grapevine leaves of the ‘Graševina’ cultivar on carbonate soil was conducted in a two-year study in 2018 and 2019. The experiment was settled in three replicates on a total of seven fertilization treatments that differed in used form of nitrogen fertilizer and foliar application of Fe before and after the flowering of the grapevine: control (C); calcium ammonium nitrate (KAN); calcium ammonium nitrate + foliar Fe (KAN+F); ammonium sulfate (AS); ammonium sulfate + foliar Fe (AS+F); ammonium sulfonitrate + foliar Fe (ASN+F); urea + foliar Fe (U+F). Mineral fertilization with acid-forming nitrogen fertilizers (AS and ASN) significantly affected local acidification of alkaline soil, i.e., reducing the actual and exchangeable soil pH reaction, which resulted in increased soil Fe availability. Despite the increase in soil iron availability, no increased iron bioaccumulation in the grapevine leaves was found in the flowering and veraison stages at treatments where foliar fertilization was omitted. Of all the observed treatments, only foliar fertilization had a positive effect on iron concentration in the grapevine leaves, which leads to the conclusion that this is an effective way to solve iron deficiency symptoms and chlorosis occurrence. The use of mineral fertilizers with acid-forming nitrogen fertilizers for many years can result in a reduction of required foliar treatments and thus significantly affect the ecological and economic aspects of grape production. Thus, integrated iron management is needed to meet the needs of the grapevine for this micronutrient and to reduce the occurrence of leaf chlorosis in carbonate soil.

Identifying Individual Nutrient Deficiencies of Grapevine Leaves Using Hyperspectral Imaging

The efficiency of a vineyard management system is directly related to the effective management of nutritional disorders, which significantly downgrades vine growth, crop yield and wine quality. To detect nutritional disorders, we successfully extracted a wide range of features using hyperspectral (HS) images to identify healthy and individual nutrient deficiencies of grapevine leaves. Features such as mean reflectance, mean first derivative reflectance, variation index, mean spectral ratio, normalised difference vegetation index (NDVI) and standard deviation (SD) were employed at various stages in the ultraviolet (UV), visible (VIS) and near-infrared (N.I.R.) regions for our experiment. Leaves were examined visually in the laboratory and grouped as either healthy (i.e. control) or unhealthy. Then, the features of the leaves were extracted from these two groups. In a second experiment, features of individual nutrient-deficient leaves (e.g., N, K and Mg) were also analysed and compared with those of control leaves. Furthermore, a customised support vector machine (SVM) was used to demonstrate that these features can be utilised with a high degree of effectiveness to identify unhealthy samples and not only to distinguish from control and nutrient deficient but also to identify individual nutrient defects. Therefore, the proposed work corroborated that HS imaging has excellent potential to analyse features based on healthiness and individual nutrient deficiencies of grapevine leaves.

VOCs Are Relevant Biomarkers of Elicitor-Induced Defences in Grapevine

Grapevine is susceptible to fungal diseases generally controlled by numerous chemical fungicides. Elicitors of plant defence are a way of reducing the use of these chemicals, but still provide inconsistent efficiency. Easy-to-analyse markers of grapevine responses to elicitors are needed to determine the best conditions for their efficiency and position them in protection strategies. We previously reported that the elicitor sulphated laminarin induced the emission of volatile organic compounds (VOCs) by grapevine leaves. The present study was conducted to characterise and compare VOC emissions in response to other elicitors. Bastid® was first used to test the conditions of VOC collection and analysis. Using SBSE-GC-MS, we detected several VOCs, including the sesquiterpene α-farnesene, in a time-dependent manner. This was correlated with the induction of farnesene synthase gene expression, in parallel with stilbene synthesis (another defence response), and associated to resistance against downy mildew. The other elicitors (Redeli®, Romeo®, Bion®, chitosan, and an oligogalacturonide) induced VOC emission, but with qualitative and quantitative differences. VOC emission thus constitutes a response of grapevine to elicitors of various chemical structures. Therefore, VOC analysis is relevant for studying the impact of environmental factors on grapevine defence responses and optimising the performance of elicitors in vineyards.

Zinc Concentration and Distribution in Vineyard Soils and Grapevine Leaves from Valdepeñas Designation of Origin (Central Spain)

(1) Background: The purpose of this study was to investigate zinc contents in leaves and soils of the Valdepeñas Protected Designation of Origin (PDO), situated in central Spain. Zn distribution maps of leaves and soils were obtained. (2) Methods: Ninety soil profiles were described, sampled and analyzed. Furthermore, vineyard leaves were collected randomly in each of the analyzed soil vineyard profiles. Soil and leaf samples were analyzed by X-ray fluorescence. (3) Results: The mean total Zn concentrations in vineyard soils were in the range of 16.2–153.7 mg·kg−1, with a mean of 47.5 mg·kg−1. The obtained values above the 95th percentile (between 81.3 and 153.7 mg·kg−1) could be affected by different parent materials or Zn agricultural treatments in vineyards. Contents in different soils follow the order Entisol > Alfisol > Inceptisol. The average Zn content value in leaves was 23.8 mg·kg−1 and oscillated between 11.5 and 93.3 mg·kg−1; minor differences were detected between soil types, with the highest value in plants grown on soils without carbonates. (4) Conclusions: The obtained values are optimal for vine cultivation. The bioaccumulation factors in leaves were lower than unity (0.24–0.53 range). This means that the Zn bioaccumulation process is relatively low in the soil–grapevine system. This study serves as a reference to identify areas that present Zn deficiencies or risk of contamination.

Retention and Transmission of Grapevine Leafroll-Associated Virus 3 by Pseudococcus calceolariae

Grapevine leafroll-associated virus 3 (GLRaV-3), an economically significant pathogen of grapevines, is transmitted by Pseudococcus calceolariae, a mealybug commonly found in New Zealand vineyards. To help inform alternative GLRaV-3 control strategies, this study evaluated the three-way interaction between the mealybug, its plant host and the virus. The retention and transmission of GLRaV-3 by P. calceolariae after access to non-Vitis host plants (and a non-GLRaV-3 host) White clover (Trifolium repens L. cv. “Grasslands Huia white clover”), Crimson clover (T. incarnatum), and Nicotiana benthamiana (an alternative GLRaV-3 host) was investigated. For all experiments, P. calceolariae first instars with a 4 or 6 days acquisition access period on GLRaV-3-positive grapevine leaves were used. GLRaV-3 was detected in mealybugs up to 16 days on non-Vitis plant hosts but not after 20 days. GLRaV-3 was retained by second instars (n = 8/45) and exuviae (molted skin, n = 6/6) following a 4 days acquisition period on infected grapevines leaves and an 11 days feeding on non-Vitis plant hosts. Furthermore, GLRaV-3 was transmitted to grapevine (40−60%) by P. calceolariae second instars after access to white clover for up to 11 days; 90% transmission to grapevine was achieved when no alternative host feeding was provided. The 16 days retention period is the longest observed in mealybug vectoring of GLRaV-3. The results suggest that an alternative strategy of using ground-cover plants as a disrupter of virus transmission may be effective if mealybugs settle and continue to feed on them for 20 or more days.