Downy Mildew Research Articles

Priming grapevines with oregano essential oil vapour results in a metabolomic shift eliciting resistance against downy mildew

BackgroundPriming plants with natural products is extensively studied in the agricultural field to reduce the use of synthetic and copper-based pesticides. Previous studies have shown that Oregano essential oil vapour (OEOV) is an effective priming agent against downy mildew (DM) in grapevine (Vitis vinifera L. cv. Chasselas), activating different transcriptomic regulated defence mechanisms.ResultsIn the present study, we complement transcriptomic data with metabolomic insights, confirming some previous regulating patterns and highlighting new mechanisms underlying OEOV-induced resistance. A significant modulation of the phenylpropanoid pathway was noted. The data also confirmed the induction of an oxidative stress response indicated by an up-regulation of reactive oxygen species (ROS)-related genes and a congruent depletion of putative L-glutathione. Interestingly, OEOV promoted the accumulation of organic metabolites such as terpenes and other potential phytoalexins, which could potentially contribute to grapevine innate immune response to Plasmopara viticola.ConclusionOverall, this study uncovered a diverse influence of OEOV on V. vinifera defence mechanisms against DM, enhancing our comprehension of the mode of action of essential oils. This insight offers various prospects for crafting innovative biocontrol products, fostering a more dynamic and sustainable approach to agriculture.

Screening Sorghum Breeding Lines for Identification of Resistance Sources for Multiple Fungal Diseases

Sorghum is a dual purpose crop; both grain and fodder are highly valued for human and animal consumption respectively. However, the crop is vulnerable for many fungal diseases of which downy mildew, rust and grain moldshave become major concern in Dharwad district of North Karnataka revealing impact on sorghum yield. New and alternate sources of host plant resistance are needed for successful management of these diseases. Host plant resistance is the best practice to enable the crop to tolerate diseases which aid in increasing yield. This study aimed to identify the resistant sources against these foliar diseases. About hundred sorghum entries were evaluated under natural unprotected conditions for three continuous years by providing feasible environmental conditions for respective pathogen growth in order to identify resistant sources for downy mildew, rust and grain mold diseases. The incidence of the downy mildew disease was recorded followed by grade for estimation of reaction to downy mildew. However, rust (top four leaves will be considered) and grain mold disease severity was scored using the disease severity rating scale i.e., 1-9 scale at physiological maturity. Among the different entries evaluated, some of the entries viz., SVD-1621, SVD–1503Kand SVD–1411Kshowed multiple disease resistance with reaction varied from resistant to moderately resistant to sorghum downy mildew, rust and grain mold.

Гибрид подсолнечника Лаврус с устойчивостью к сульфонилмочевиновым гербицидам и заразихе

The hybrid Lavrus is purposed for cultivation in a production system with after-seedling sulphonyl-urea herbicides with an acting ingredient tribenuron-methyl. The hybrid Lavrus belongs to the middle-early maturity group, is characterized with high yields, resistance to a broomrape race G and downy mildew pathogen (races 330, 710, 730, 334, and 734). The growing season is 110 days till harvesting maturity, oil content in seeds is equal to 49% and huskness 25%. It is genetically similar the hybrid Tiazar.

Recombination landscape and karyotypic variations revealed by linkage mapping in the grapevine downy mildew pathogen Plasmopara viticola.

Plasmopara viticola, the causal agent of grapevine downy mildew, is a biotrophic oomycete engaged in a tight coevolutionary relationship with its host. Rapid adaptation of the pathogen is favored by annual sexual reproduction that generates genotypic diversity. With the aim of studying the recombination landscape across the P. viticola genome, we generated 2 half-sibling F1 progenies (N = 189 and 162). Using targeted SNP sequencing, between 1,405 and 1,894 markers were included in parental linkage maps, and a consensus map was obtained by integrating 4,509 markers. The reference genome could be assembled into 17 pseudochromosomes, anchoring 88% of its physical length. We observed a strong collinearity between parental genomes and extensive synteny with the downy mildew Peronospora effusa. In the consensus map, the median recombination rate was 13.8 cM/Mb. The local recombination rate was highly variable along chromosomes, and recombination was suppressed in putative centromeric regions. Recombination rate was found negatively correlated with repeats' coverage and positively correlated with gene coverage. However, genes encoding secreted proteins and putative effectors were underrepresented in highly recombining regions. In both progenies, about 5% of the individuals presented karyotypic anomalies. Aneuploidies and triploidies almost exclusively originated from the male-transmitted chromosomes. Triploids resulted from fertilization by diploid gametes, but also from dispermy. Obligatory sexual reproduction each year may explain the lower level of karyotypic variation in P. viticola compared to other oomycetes. The linkage maps will be useful to guide future de novo chromosome-scale assemblies of P. viticola genomes and to perform forward genetics.

Use of Innovative Compounds to Manage Grapevine Downy and Powdery Mildews: Results of a Three-Year Field Trial

Induced resistance (IR) based on elicitors application aims to strengthen plant defenses, rather than directly targeting pathogens. These compounds are less toxic than conventional pesticides and are useful in reducing their use. Strategies based on COS–OGA, Swinglea glutinosa, and low copper doses were tested in this three-year (2021–2023) field investigation against grapevine downy (DM) and powdery (PM) mildew. Their effectiveness was compared to copper, sulfur, untreated, and water-sprayed plants in a naturally infected vineyard. Combined treatments provided higher levels of protection. COS–OGA at 2 L ha−1 combined with low copper doses and an adjuvant protected canopy and production from both DM and PM at the same level as copper and farm application (based on copper and sulfur). In favorable seasons, 2023 for DM and 2022 for PM, this strategy reduced the DM McKinney Index compared to untreated plants by 74% and 39% on leaves and bunches, respectively. Reductions observed for PM were 85% on leaves and 46% on bunches. S. glutinosa showed reductions only in one assessment against PM on bunches. This work validates IR-based DM and PM management strategies under field conditions and paves the way toward concrete reduction in copper and sulfur use in vineyards.

Do plant resistance inducers reduce Plasmopara viticola infection on grapevine berry clusters at different growth stages?

Plant resistance inducers (PRIs) are promising alternatives to chemical fungicides. Their effectiveness against grapevine downy mildew (DM) has been demonstrated for leaves, yet research on berry clusters is limited. We investigated the efficacy of six PRIs on clusters of cv. Barbera and Merlot from the end of flowering (growth stage GS 69) to fruit setting (GS 71) and inoculated with a sporangial suspension of Plasmopara viticola (Pv) at 1, 3, 6, 12, and 19 days after treatment (DAT). Cerevisane (CER) and Pythium oligandrum (PYT) did not reduce DM severity compared to the nontreated control (NT). Fosetyl-Al (FOS) reduced DM severity at 1-6 DAT, with >50% reduction compared to NT. Laminarin (LAM) was effective at 6, 12, and 19 DAT, with 42.7%-to 50.0% efficacy compared to NT, while cos-oga (COS) and K-phosphonate (PHO) were effective at 12 and 19 DAT (60% efficacy). PRIs were also applied to clusters at initial flowering (GS 60), GS 69-71, and pea-sized berries (GS 75), which were then inoculated with Pv at 7 DAT. At GS 60, treatments with LAM and PHO reduced disease severity compared to NT by 77.5% and 83.6%, respectively. At GS 69-71, LAM, PHO, and FOS caused 54.7%-75.7% disease reduction. At GS 75, all PRIs exhibited a disease reduction > 75%. The efficacy of PRIs increased as the cluster developmental stage advanced, indicating an interaction with the ontogenic resistance of berries. Our results are relevant for the practical use of PRIs in protecting grapevine clusters from DM.

Cryo-EM Structures Reveal the Unique Binding Modes of Metyltetraprole in Yeast and Porcine Cytochrome bc1 Complex Enabling Rational Design of Inhibitors.

Cytochrome bc1 (complex III) represents a significant target for the discovery of both drugs and fungicides. Metyltetraprole (MET) is commonly classified as a quinone site inhibitor (QoI) that combats the G143A mutated isolate, which confers high resistance to strobilurin fungicides such as pyraclostrobin (PYR). The binding mode and antiresistance mechanism of MET remain unclear. Here, we determined the high-resolution structures of inhibitor-bound S. cerevisiae complex III (MET, 2.52 Å; PYR, 2.42 Å) and inhibitor-bound porcine complex III (MET, 2.53 Å; PYR, 2,37 Å) by cryo-electron microscopy. The distinct binding modes of MET and PYR were observed for the first time. Notably, the MET exhibited different binding modes in the two species. In S. cerevisiae, the binding site of MET was the same as PYR, serving as a Pm-type inhibitor of the Qo site. However, in porcine, MET acted as a dual-target inhibitor of both Qo and Qi. Based on the structural insights, a novel inhibitor (YF23694) was discovered and demonstrated excellent fungicidal activity against downy mildew and powdery mildew fungi. This work provides a new starting point for the design of the next generation of inhibitors to overcome the resistance.

FIRST IDENTIFICATION OF DOWNY MILDEW ON QUINOA (PERONOSPORA FARINOSA F. SP. CHENOPODII) IN ROMANIA: PRELIMINARY RESEARCH

With the expansion of quinoa cultivation (Chenopodium quinoa Willd.) into new areas, including Romania, it is expected that specific diseases will emerge. Currently, downy mildew is the most significant and studied disease affecting quinoa worldwide. This research was conducted in the experimental fields of the UASVM of Bucharest, under the climatic conditions of the 2024 growing season. Two quinoa varieties, supplied by Quinoa Quality ApS, Denmark, were evaluated for their response to the pathogen Peronospora farinosa f. sp. chenopodii. The first detection of downy mildew in quinoa in our country provides an important update to phytopathological research on this crop, which offers numerous economic advantages in the current climate context. The characteristic symptoms of the disease caused by the pathogen Peronospora farinosa f. sp. chenopodii are described. Vikinga was susceptible to downy mildew (AD 6.6%), while Puno showed an insignificant degree of leaf infection (AD 0.65%).

Triazole Sulfonamide Derivates: Inhibitors of the bc1 Complex to Control Cucumber Downy Mildew.

Cucumber downy mildew (CDM), caused by Pseudoperonospora cubensis, is a destructive disease that affects greenhouse cucumbers and causes significant losses for growers. Amisulbrom, a triazole sulfonamide fungicide targeting the Qi site in the bc1 complex, has shown potential in effectively combating CDM. However, its detailed binding mode with the target is unclear. In this study, a three-dimensional (3D) structure of the bc1 complex from P. cubensis was built, and its interaction with amisulbrom was investigated by integrating molecular docking, molecular dynamics, and molecular mechanics/Poisson-Boltzmann surface area (MM/PBSA) methods. Based on the binding mode of amisulbrom with the Pc-bc1 complex, a scaffold hopping strategy was performed, and compounds 11a-o and 12a-v were designed. Among them, compound 12g showed excellent fungicidal properties against CDM in field trials. The present work indicated that the oxime ether moiety could be further optimized for better results. Furthermore, compound 12g has the potential to serve as a lead compound in the search for new Qi-site inhibitors of the bc1 complex.

Downy mildew effector HaRxL106 interacts with the transcription factor BIM1 altering plant growth, BR signaling and susceptibility to pathogens.

Hyaloperonospora arabidopsidis (Hpa) is an oomycete pathogen that causes downy mildew disease on Arabidopsis. This obligate biotroph manipulates the homeostasis of its host plant by secreting numerous effector proteins, among which are the RxLR effectors. Identifying the host targets of effectors and understanding how their manipulation facilitates colonization of plants are key to improve plant resistance to pathogens. Here we characterize the interaction between the RxLR effector HaRxL106 and BIM1, an Arabidopsis transcription factor (TF) involved in Brassinosteroid (BR) signaling. We report that HaRxL106 interacts with BIM1 in vitro and in planta. BIM1 is required by the effector to increase the host plant susceptibility to (hemi)biotrophic pathogens, and thus can be regarded as a susceptibility factor. Mechanistically, HaRxL106 requires BIM1 to induce the transcriptional activation of BR-responsive genes and cause alterations in plant growth patterns that phenocopy the shade avoidance syndrome. Our results support previous observations of antagonistic interactions between activation of BR signaling and suppression of plant immune responses and reveal that BIM1, a new player in this crosstalk, is manipulated by the pathogenic effector HaRxL106.

Droplet Digital PCR: A New Molecular Method to Detect G1105S/V Mutations in Plasmopara viticola CesA3 Gene.

Plasmopara viticola is the causal agent of Grapevine Downy Mildew (GDM), which is a devastating disease of grapevines in humid temperate regions. The most employed method for protecting grapevines against GDM is the application of chemical fungicides. In Spain, Carboxylic Acid Amides (CAAs) are a fungicide group currently utilized in GDM control. In P. viticola, resistance to CAAs is conferred by G1105S and G1105V mutations in the CesA3 gene. Droplet digital polymerase chain reaction (ddPCR) is an innovative technique that combines PCR and droplet microfluidics to disperse the sample into thousands of water-in-oil droplets in which an amplification reaction is individually performed. In this study, we set up a ddPCR protocol to quantify S1105 and V1105 mutations conferring resistance to CAAs in P. viticola. The optimal PCR conditions were established, and the sensitivity and precision of the protocol were assessed. Four P. viticola populations coming from commercial vineyards in northern Spain were analyzed, and different allele frequencies were found in the analyzed samples corresponding to the different fungicide management strategies, ranging from 7.72% to 100%. Knowing the level of mutated alleles allows for designing resistance management strategies suited for each location. This suggests that similar ddPCR assays could be developed for studying mutations implicated in fungicide resistance in other fungicide groups and plant pathogens.

Correlation and Regression Analyses of Disease and Agronomic Traits of Ethiopian Mustard (Brassica Carinata A. Braun.) Genotypes

Ethiopian mustard (<i>Brassica carinata A. Braun</i>) is an important oilseed crop with significant potential for food and energy production. The study evaluated 36 genotypes using a 6 x 6 lattice design to analyze correlations and regression among traits, aiming to understand their relationships and identify key traits for developing high-performing varieties. The analysis of variance revealed significant variation (p < 0.001) for traits including seed yield, flowering time, maturity date, disease resistance, thousand seed weight, oil content and oil yield; indicating the potential for genetic improvement. However, traits such as downy mildew resistance, leaf spot and branching showed non-significant variation, suggesting these traits may be more influenced by environmental factors than by genetic differences among the genotypes. Pearson correlation coefficients highlighted significant relationships among traits. Days to flowering (r = 0.687) and maturity (r = 0.029) positively correlated with yield, while disease traits negatively impacted seed yield. Notably, Thousand Seed Weight (r = 0.985) strongly correlated with yield, underscoring the importance of seed size. A multiple regression model explained 99.7% of the variation in seed yield, with a highly significant intercept (1863.35, p < 0.001). Key associations were found with secondary branches (12.32), oil content (-46.79) and oil yield (2.19). This study confirms the potential for improving Ethiopian mustard yield through genetic selection of key traits. It is recommended that breeding programs focus on enhancing seed size and disease resistance while considering environmental factors to maximize yield potential.

Downy mildew of millets - An overview

Amidst global food insecurity, malnutrition, agricultural challenges, and climate change, millet farming is emerging as a viable alternativedue to its high nutritional value, resilience to extreme weather conditions, and adaptability to marginal soils. Often referred to as “super-crops”, millets gained international recognition in March 2021 during the 75th session of the United Nations General Assembly. Millets rank among the most important crops globally, following rice, wheat, maize, and sorghum. However, they are susceptible to more than fifty diseases, with the most destructive being ‘Downy Mildew’. This disease is caused by oomycete pathogens such as Sclerospora graminicola, Peronosclerospora sorghi and Sclerophthora macrospora, posing a significant threat to millet production, with yield losses ranging from 50% to 100%. This review emphasizes the importance of millet and the devastating effects of downy mildew on its yields. It explores the physiological and histological changes induced by the disease, the characterization of effector protein, and the genetic variability in millet populations. Additionally, various management techniques for combating downy mildew are examined, including chemical treatments, induced resistance, organic-based approaches, cultural practices, resistant genotypes, and advancements in nanotechnology. By compiling current knowledge on millet disease and effective management strategies, this review aims to serve as a comprehensive resource for researchers and farmers, supporting sustainable millet farming and improving global food security.

Temporal Dynamics of Two Genetically Diverse Downy Mildew Mitochondrial Clades on Cucumber Cultivars in South Carolina and Florida

Downy mildew (DM, Pseudoperonospora cubensis) is an important disease that can significantly reduce yield of field-grown cucumbers in the US. Cucumber cultivars with resistance to DM were widely grown for >30 years. However, resistance broke down in 2004 resulting in severe DM epidemics. Large plot trials were conducted to characterize pathogen virulence and population dynamics on DM tolerant cultivars Peacemaker and Expedition and susceptible SMR-58 in Charleston, SC and Fort Pierce, FL in 2016 and 2017. Rapid DM development on SMR-58 was observed at both locations in 2016 and 2017. Disease progress on Expedition and Peacemaker were slow as compared to SMR-58 in Fort Pierce, FL in 2016. Very low to no DM was observed on Peacemaker or Expedition in Charleston in 2016. In 2017, all cultivars were affected in Charleston, but only SMR-58 had severe DM (95-100%) in Fort Pierce. Pathogen population analysis using DM specific mitochondrial clade (MC1 and MC2) markers showed differences between the P. cubensis populations across location and years on the cucumber cultivars. Both MC1 and MC2 were detected in cucumber plots in SC and FL. The most prevalent DM mitochondrial clade in SC during June 2016 was MC1 primarily on SMR-58 (95-100%). However, in July 2016 that population shifted towards MC2 (45-77%). This suggested that the DM populations can change relatively quickly when suitable environment favors. Mixed populations of MC1 and MC2 continued to be observed in following year in Charleston, SC in 2017. In Fort Pierce, FL a complete shift was observed from MC2 in 2016 to MC1 in 2017. Since both MCs are present in the southeastern United States either at the same time or possibly different times during the production year, cultivars with combined resistance to P. cubensis populations will be needed to reduce reliance on fungicides to manage DM.

Cover crops lower the dispersal of grapevine foliar pathogens from the ground and contribute to early-season disease management.

Currently, fungicides are widely used to control grapevine foliar diseases. This study explored the possibility of decreasing the use of fungicides to control these diseases using cover crops in the inter-row of vineyards. In small-scale experiments, we found that cover crops (namely horseradish Armoracia rusticana) were able to (i) reduce the numbers of airborne conidia of Botrytis cinerea (originating from an inoculum source above the soil) escaping the cover canopy by >85% with respect to the base soil and (ii) reduce the number of raindrops impacting the soil by 46%-74%, depending on the cover crop height and rain-originated splash droplets that escaped from the ground by 75%-95%, which reduced splash-borne inoculum. In two organic vineyards, for 2 years, fall- (mixture of Lolium perenne, Onobrychis viciifolia, and Trifolium repens) or spring-sown (a mixture of Vicia sativa and Sinapis sp.) cover crops could significantly delay (by 14-30 days) and reduce (till >90%) the development of downy and powdery mildew epidemics. This effect was more evident in plots untreated with fungicides than in treated plots. Cover crops also delayed the onset of epidemics depending on the type of cover crop and disease. Cover crops did not negatively affect grape yield and quality. Overall, the results showed that the introduction of cover crops in vineyard management can significantly contribute to disease control by lowering the load from ground to grapevine canopies of pathogen inocula, delaying disease onset, and reducing diseases severity during the season.

Biocontrol of plant pathogens by Lysobacter enzymogenes isolate LEC: efficacy of shake flask broth, fermentation broth and dried preparations

ABSTRACT The aim of our study was to upscale the production of Lysobacter enzymogenes strain LEC from shake flasks to a laboratory bioreactor. The obtained fermentation broth was to be downstream-processed by lyophilisation and fluidised bed-drying, followed by testing of the dried preparations against plant pathogens. Different batches of broth from shake flasks and from individual fermenter runs were characterised and compared. Number of viable cells, in vitro efficacy (ED90 value) against the apple scab pathogen Ventura inaequalis, as well as efficacy against Phytophthora infestans on potato plants were all reproducible and not impaired by upscaling the production volume from shake flask to the bioreactor. Fermentation broth was processed by lyophilisation and fluidised bed-drying. In bioassays, the activity against downy mildew (Pseudoperonospora cubensis) on cucumber were comparable for the unformulated fermentation broth and the fluidised bed-dried product, while the lyophilised product was significantly more effective. Strain LEC showed reproducible pathogen suppressive activity, independent from production scale and batch. Production upscaling and formulation by drying are possible without loss of efficacy.

Transcription-Aided Selection (TAS) for Crop Disease Resistance: Strategy and Evidence.

A transcription-aided selection (TAS) strategy is proposed in this paper, which utilizes the positive regulatory roles of genes involved in the plant immunity pathways to screen crops with high disease resistance. Increased evidence has demonstrated that upon pathogen attack, the expression of diverse genes involved in salicylic acid (SA)-mediated SAR are differentially expressed and transcriptionally regulated. The paper discusses the molecular mechanisms of the SA signaling pathway, which plays a central role in plant immunity, and identifies differentially expressed genes (DEGs) that could be targeted for transcriptional detection. We have conducted a series of experiments to test the TAS strategy and found that the level of GmSAGT1 expression is highly correlated with soybean downy mildew (SDM) resistance with a correlation coefficient R2 = 0.7981. Using RT-PCR, we screened 2501 soybean germplasms and selected 26 collections with higher levels of both GmSAGT1 and GmPR1 (Pathogenesis-related proteins1) gene expression. Twenty-three out of the twenty-six lines were inoculated with Peronospora manshurica (Pm) in a greenhouse. Eight showed HR (highly resistant), four were R (resistant), five were MR (moderately resistant), three were S (susceptible), and three were HS (highly susceptible). The correlation coefficient R2 between the TAS result and Pm inoculation results was 0.7035, indicating a satisfactory consistency. The authors anticipate that TAS provides an effective strategy for screening crops with broad-spectrum and long-lasting resistance.

CRISPR/Cas9‐Mediated Genome Editing for Trait Improvement and Stress Tolerance in Leguminosae (Legume Family)

ABSTRACTLegumes represent a significant source of protein, roughage, minerals and carbohydrates in global diets. They are cultivated primarily for human consumption, forage and as a green manure. However, the growth and productivity of legumes are often hindered by a range of biological and environmental factors. The most prevalent diseases afflicting legumes include downy mildew, fusarium root rot, southern blight and common leaf spot. Additionally, environmental stresses such as salinity and drought represents significant challenges. Over time, the development of cultivars with enhanced tolerance has emerged as a sustainable approach to combat the impact of these stresses. Although environmentally friendly, traditional breeding methods entail lengthy screening and cross‐breeding protocols, which constrain their efficacy in addressing climate challenges and ensuring global food security. Furthermore, these approaches rely on the natural availability of genetic variation, which may not always be exist for specific traits, particularly in the context of rapidly changing environmental conditions. Additionally, the traditional breeding method is not sufficiently precise, which can result in the unintended introduction of undesirable traits. Furthermore, the genetic intricacy of legumes presents an additional challenge making it difficult to isolate and enhance desired traits. These constrain impede the capacity to expeditiously develop cultivars that can withstand emerging stresses, such as climate change. Genome editing has emerged as a powerful tool to overcome the limitations of traditional breeding methods. By enabling precise and targeted genetic manipulation, genome editing can enhance desired traits or introduce new ones, thereby facilitating the development of climate‐resilient agronomic varieties. In particular, clustered regularly interspaced short palindromic repeat/CRISPR associated protein (CRISPR/Cas9)‐mediated editing has demonstrated considerable potential in enhancing legume adaptability to diverse stress conditions and increasing crop yield. This study highlights the advancements in genome editing, with a specific focus on CRISPR/Cas9 technology, as a means to improve legume crops' resilience and productivity in response to environmental pressures.

Discovery of Acaricidal, Insecticidal, and Fungicidal Candidates Inspired by Natural Ethyl Cinnamate Compounds Isolated from Polygonum orientale L.

As a continuation of our research on the pesticide development of Polygonum orientale L., the chemical constituents of the seeds of P. orientale were systematically investigated. Eleven natural compounds (PO-1 to PO-11) were isolated from the EtOAc extract of P. orientale. Notably, compound PO-9 and its dimeric compound PO-10 were first isolated from P. orientale and possessed excellent acaricidal activity against Tetranychus cinnabarinus. With PO-9 and PO-10 as the lead compounds, two series of cinnamate derivatives were further synthesized, and their acaricidal, insecticidal, and fungicidal activities were evaluated systematically. The insecticidal activity results showed that dimeric derivative NKY-70 displayed the highest acaricidal activity against T. cinnabarinus and insecticidal activities against Brevicoryne brassicae and Myzus persicae. Furthermore, most of these compounds showed excellent in vitro antifungal activity against plant fungi. Compound NKY-66 displayed the highest and broad spectrum of antifungal activity against 23 fungi, and the respective EC50 values were 0.09, 0.08, 0.12, 0.18, 0.12, and 0.09 mg/mL against Valsa mali, Fusarium oxysporum f. sp. cucumerinum, Fusarium graminearum, Magnaporthe oryzae, Colletotrichum capsici, and Phytophthora infestans, which were more potent than those of chlorothalonil and procymidone. Moreover, the in vivo fungicidal evaluation also demonstrated that compound NKY-66 could effectively control plant fungal diseases in the greenhouse and in the field, such as damping off, powdery mildew, and cucumber downy mildew. Therefore, these findings implied that the cinnamate derivative NKY-66 displayed superior in vitro and in vivo fungicidal activities and could be a potential candidate against plant fungal diseases.

Efficacy of using grape cane extracts against <i>Plasmopara viticola</i> under field conditions and their impact on the composition of berries and musts of <i>Vitis vinifera</i> L. cv. Riesling

Grapevine downy mildew caused by Plasmopara viticola is a deleterious vine disease currently controlled using synthetic and copper-based fungicides. Environmental concerns surrounding such fungicides necessitate sustainable alternatives like grape cane extracts. However, studies into their efficacy and effects on the product remain limited. This study aimed to assess the open-field efficacy of a novel grape cane extract formulation, alone and combined with a copper agent, against downy mildew, and to examine its impact on berry and must composition. The results were compared to standard fungicides frequently used in integrated and organic viticulture. In 2022, the grape cane extract formulation reduced downy mildew severity by 78 % on berry clusters, comparable to the maximum acceptable dose of copper for organic farming in Germany (3 kg/ha/a). Combining the grape cane extract with the copper agent was more effective than the copper agent alone, but not more effective than the grape cane extract alone. In 2023, disease development was marginal, despite artificial inoculation. Compositional differences detectable by FTIR were insignificant between musts derived from all treatments, increased copper levels were observed whenever copper had been applied. The phenolic content in freeze-dried, de-seeded berries of 2022 was significantly lower after copper (14.6 mg/g dry weight DW) and grape cane extract treatments (6.6 mg/g DW) when compared to the control (36.1 mg/g DW), with discrepancies in stilbenoid and flavan-3-ol levels in particular, as analysed by HPLC-DAD. However, these differences were not confirmed in 2023, with results showing no correlations between different treatments and phenolic contents. These findings suggest that applications of the phenolic grape cane extract do not lead to artificially altered levels or relevant residues of the active constituents; i.e., the phenolic compounds in the product. In brief, grape cane extracts might represent a promising natural alternative to controlling grapevine downy mildew, particularly in organic viticulture, which, to date, heavily relies on (eco-)toxic copper-pesticides. Further multi-year studies including wine analyses are warranted to follow the entire flow towards the final product.