In Vitro Collection for the Safe Storage of Grapevine Hybrids and Identification of the Presence of Plasmopara viticola Resistance Genes

This paper focuses on the creation of an in vitro collection of grapevine hybrids from the breeding program of the Kazakh Scientific Research Institute of Fruit Growing and Viticulture and investigates the presence of Plasmopara viticola resistance mediated by Rpv3 and Rpv12 loci. We looked at the optimization of in vitro establishment using either shoots taken directly from field-grown plants or from budwood cuttings forced indoors. We further screened for the presence of endophyte contamination in the initiated explants and optimized the multiplication stage. Finally, the presence of the resistance loci against P. viticola was studied. The shoots initiated from the field-sourced explants were the more effective method of providing plant sources for in vitro initiation once all plant accessions met the goal of in vitro establishment. The concentration of phytohormones and the acidity of the culture medium have a great effect on the multiplication rate and the quality of in vitro stock cultures. Out of 17 grapevine accessions, 16 showed the presence of single or combined resistance loci against P. viticola. The grapevine accessions identified as carrying Rpv3 and Rpv12 alleles represent important genetic resources for disease resistance breeding programs. These accessions may further contribute to the creation of new elite cultivars of economic interest.

Monoglucoside versus Diglucoside Anthocyanin Evolution of Red Wine Produced Using a Fungus-Resistant Grape Cultivar (Downy Mildew and Powdery Mildew) under Oxidative Conditions

The need to reduce the use of pesticides in viticulture is increasing the interest in wines produced using fungal-resistant grapevine varieties, which are characterized by relevant contents of both monoglucoside and diglucoside anthocyanins. Aging in wooden barrels induces oxygen permeation into wine, but little is known about diglucoside anthocyanin evolution. Cabernet cortis wine was subjected to addition of oxygen and oak chips, and the anthocyanin changes were followed for 1 month. Decreases of 90% total monoglucosides, 80% acylated monoglucosides, 65% diglucosides, and 90% acylated diglucosides were observed. Monoglucosides formed pyranoanthocyanins, and the lower steric hindrance favored their polymerization with flavanols. Instead, the decrease in diglucosides was correlated to the number of hydroxyl groups of ring B, indicating the predominant oxidation of aglycones. However, three flavonol-anthocyanin-diglucoside derivatives named (epi)catechin-ethyl-Mv-dihexoside, (epi)catechin-ethyl-Pn-dihexoside, and (epi)catechin-Mv-dihexoside A-type were identified in wine for the first time. These research findings are useful for tuning suitable oenological practices to stabilize the color of these wines (type of barrel, aging times, oxygenation practices) and lower the malvin content, which currently is recommended by the OIV at a maximum of 15 mg/L and is a critical issue for their commercialization.

CRISPR/Cas9 editing of Downy mildew resistant 6 (DMR6-1) in grapevine leads to reduced susceptibility to Plasmopara viticola

Downy mildew of grapevine (Vitis vinifera), caused by the oomycete Plasmopara viticola, is an important disease that is present in cultivation areas worldwide, and using resistant varieties provides an environmentally friendly alternative to fungicides. DOWNY MILDEW RESISTANT 6 (DMR6) from Arabidopsis is a negative regulator of plant immunity and its loss of function confers resistance to downy mildew. In grapevine, DMR6 is present in two copies, named VvDMR6-1 and VvDMR6-2. Here, we describe the editing of VvDMR6-1 in embryogenic calli using CRISPR/Cas9 and the regeneration of the edited plants. All edited plants were found to be biallelic and chimeric, and whilst they all showed reduced growth compared with non-transformed control plants, they also had reduced susceptibility to P. viticola. Comparison between mock-inoculated genotypes showed that all edited lines presented higher levels of salicylic acid than controls, and lines subjected to transformation presented higher levels of cis-resveratrol than controls. Our results identify VvDMR6-1 as a promising target for breeding grapevine cultivars with improved resistance to downy mildew.

Sensitivity of Plasmopara viticola to selected fungicide groups and the occurrence of the G143A mutant in Australian grapevine isolates

BACKGROUND

Grapevine downy mildew, caused by Plasmopara viticola, is an economically important disease in Australia and worldwide. The application of fungicides is the main tool to control this disease. Frequent fungicide applications can lead to the selection of resistant P. viticola populations, which has negative impacts on the management of the disease. Identification of resistance and its prevalence is necessary to inform resistance management strategies.

RESULTS

A total of 86 P. viticola isolates were collected between 2017 and 2022 from vineyards in 15 growing regions across Australia for four fungicide groups; phenylamide (PA, group 4), carboxylic acid amide (CAA, group 40), quinone outside inhibitor (QoI, group 11) and quinone outside inhibitor stigmatellin binding type (QoSI, group 45). Decreased phenotypic sensitivity was detected for all four groups, and resistance to metalaxyl-M (PA) and pyraclostrobin (QoI), was detected. Genetic analysis to detect the G143A (QoI) and G1105S (CAA) mutations using amplicon-based sequencing was performed for 239 and 65 isolates collected in 2014-2017 and 2017-2022, respectively. G143A was detected in 8% and 52% of isolates, respectively, with strong association to phenotypic resistance. However, G1105S was not detected in any isolates.

CONCLUSION

Plasmopara viticola isolates in Australia with resistance to at least two fungicide groups have been detected, therefore it is necessary to adopt resistance management strategies where resistance has been detected. Vineyards should continue to be monitored to improve management strategies for downy mildew. © 2024 Society of Chemical Industry.

Deciphering the Enhancing Impact of Exogenous Brassinolide on Physiological Indices of Melon Plants under Downy Mildew-Induced Stress

Melon (Cucumis melo L.) is a valuable horticultural crop of the Cucurbitaceae family. Downy mildew (DM), caused by Pseudoperonospora cubensis, is a significant inhibitor of the production and quality of melon. Brassinolide (BR) is a new type of phytohormone widely used in cultivation for its broad spectrum of resistance- and defense-mechanism-improving activity. In this study, we applied various exogenous treatments (0.5, 1.0, and 2.0 mg·L-1) of BR at four distinct time periods (6 h, 12 h, 24 h, and 48 h) and explored the impact of BR on physiological indices and the genetic regulation of melon seedling leaves infected by downy-mildew-induced stress. It was mainly observed that a 2.0 mg·L-1 BR concentration effectively promoted the enhanced photosynthetic activity of seedling leaves, and quantitative real-time polymerase chain reaction (qRT-PCR) analysis similarly exhibited an upregulated expression of the predicted regulatory genes of photosystem II (PSII) CmHCF136 (MELO3C023596.2) and CmPsbY (MELO3C010708.2), thus indicating the stability of the PSII reaction center. Furthermore, 2.0 mg·L-1 BR resulted in more photosynthetic pigments (nearly three times more than the chlorophyll contents (264.52%)) as compared to the control and other treatment groups and similarly upregulated the expression trend of the predicted key enzyme genes CmLHCP (MELO3C004214.2) and CmCHLP (MELO3C017176.2) involved in chlorophyll biosynthesis. Meanwhile, the maximum contents of soluble sugars and starch (186.95% and 164.28%) were also maintained, which were similarly triggered by the upregulated expression of the predicted genes CmGlgC (MELO3C006552.2), CmSPS (MELO3C020357.2), and CmPEPC (MELO3C018724.2), thereby maintaining osmotic adjustment and efficiency in eliminating reactive oxygen species. Overall, the exogenous 2.0 mg·L-1 BR exhibited maintained antioxidant activities, plastid membranal stability, and malondialdehyde (MDA) content. The chlorophyll fluorescence parameter values of F0 (42.23%) and Fv/Fm (36.67%) were also noticed to be higher; however, nearly three times higher levels of NPQ (375.86%) and Y (NPQ) (287.10%) were observed at 48 h of treatment as compared to all other group treatments. Increased Rubisco activity was also observed (62.89%), which suggested a significant role for elevated carbon fixation and assimilation and the upregulated expression of regulatory genes linked with Rubisco activity and the PSII reaction process. In short, we deduced that the 2.0 mg·L-1 BR application has an enhancing effect on the genetic modulation of physiological indices of melon plants against downy mildew disease stress.

Screening of Galician grapevine varieties by SNPs, phenotypic traits, and phytopathology

The genetic erosion of the European grapevine diversity in the last century has promoted the conservation of varieties in germplasm banks to prevent their disappearance. The study of these varieties is necessary as it would allow the diversification of the wine market, as well as provide a source of genes to face new pathogens or climate constraints. In this work, the grapevine varieties preserved in the "Estación de Viticultura e Enoloxía de Galicia" (EVEGA) Germplasm Bank (Ourense, Spain) were widely characterized, combining ampelography, ampelometry, agronomy, and phytopathology. Moreover, genetic characterization was carried out through the analysis of 48 single-nucleotide polymorphisms (SNPs). A Bayesian analysis based on the SNP data was carried out to define the genetic structure of the EVEGA Germplasm Bank, which allowed the differentiation of two main reconstructed panmictic populations (RPPs), confirming previous results obtained based on microsatellite markers (SSRs). A great diversity between varieties was found for almost every parameter evaluated for ampelography, ampelometry, phytopatology, phenology, and berry quality. A principal component analysis (PCA) performed with these phenotypical data allowed discrimination among some groups of varieties included in different genetic populations. This study allowed us to evaluate the grapevine diversity maintained in the EVEGA Germplasm Bank and characterize varieties of potential value for breeding programs of interest for the Galician viticulture.

Effect of Cucurbit Host, Production Region, and Season on the Population Structure of Pseudoperonospora cubensis in Florida

Pseudoperonospora cubensis, the causal agent of Cucurbit downy mildew (CDM), is one of the most important diseases affecting cucurbit production in the United States. This disease is especially damaging to Florida production areas, as the state is a top producer of many cucurbit species. In addition, winter production in central and south Florida likely serves as a likely source of P. cubensis inoculum for spring and summer cucurbit production throughout the eastern United States, where CDM is unable to overwinter in the absence of a living host. Over 2 years (2017 and 2018) and four seasons (spring 2017, spring 2018, fall 2017, and fall 2018), 274 P. cubensis isolates were collected from cucurbit hosts at production sites in south, central, and north Florida. The isolates were analyzed with 10 simple sequence repeat (SSR) markers to establish population structure and genetic diversity and further assigned to a clade based on a qPCR assay. Results of population structure and genetic diversity analyses differentiated isolates based on cucurbit host and clade (1 or 2). Of the isolates assigned to clade by qPCR, butternut squash, watermelon, and zucchini were dominated by clade 1 isolates, whereas cucumber isolates were split 34 and 59% between clades 1 and 2, respectively. Clade assignments agreed with isolate clustering observed within discriminant analysis of principal components (DAPC) based on SSR markers, although watermelon isolates formed a group distinct from the other clade 1 isolates. For seasonal collections from cucumber at each location, isolates were typically skewed to one clade or the other and varied across locations and seasons within each year of the study. This variable population structure of cucumber isolates could have consequences for regional disease management. This is the first study to characterize P. cubensis populations in Florida and evaluate the effect of cucurbit host and clade-type on isolate diversity and population structure, with implications for CDM management in Florida and other United States cucurbit production areas.

Underlying Mechanisms of the Hedgehog-Like Panicle and Filamentous Leaf Tissue Symptoms Caused by Sclerospora graminicola in Foxtail Millet

Downy mildew caused by Sclerospora graminicola is a systemic infectious disease affecting foxtail millet production in Africa and Asia. S. graminicola-infected leaves could be decomposed to a state where only the veins remain, resulting in a filamentous leaf tissue symptom. The aim of the present study was to investigate how S. graminicola influences the formation of the filamentous leaf tissue symptoms in hosts at the morphological and molecular levels. We discovered that vegetative hyphae expanded rapidly, with high biomass accumulated at the early stages of S. graminicola infection. In addition, S. graminicola could affect spikelet morphological development at the panicle branch differentiation stage to the pistil and stamen differentiation stage by interfering with hormones and nutrient metabolism in the host, resulting in hedgehog-like panicle symptoms. S. graminicola could acquire high amounts of nutrients from host tissues through secretion of β-glucosidase, endoglucanase, and pectic enzyme, and destroyed host mesophyll cells by mechanical pressure caused by rapid expansion of hyphae. At the later stages, S. graminicola could rapidly complete sexual reproduction through tryptophan, fatty acid, starch, and sucrose metabolism and subsequently produce numerous oospores. Oospore proliferation and development further damage host leaves via mechanical pressure, resulting in a large number of degraded and extinct mesophyll cells and, subsequently, malformed leaves with only veins left, that is, "filamentous leaf tissue." Our study revealed the S. graminicola expansion characteristics from its asexual to sexual development stages, and the potential mechanisms via which the destructive effects of S. graminicola on hosts occur at different growth stages.

Comparative Analysis of Transcriptomics and Metabolomics Reveals Defense Mechanisms in Melon Cultivars against Pseudoperonospora cubensis Infection

Melon (Cucumis melo L.) represents an agriculturally significant horticultural crop that is widely grown for its flavorful fruits. Downy mildew (DM), a pervasive foliar disease, poses a significant threat to global melon production. Although several quantitative trait loci related to DM resistance have been identified, the comprehensive genetic underpinnings of this resistance remain largely uncharted. In this study, we utilized integrative transcriptomics and metabolomics approaches to identify potential resistance-associated genes and delineate the strategies involved in the defense against DM in two melon cultivars: the resistant 'PI442177' ('K10-1') and the susceptible 'Huangdanzi' ('K10-9'), post-P. cubensis infection. Even in the absence of the pathogen, there were distinctive differentially expressed genes (DEGs) between 'K10-1' and 'K10-9'. When P. cubensis was infected, certain genes, including flavin-containing monooxygenase (FMO), receptor-like protein kinase FERONIA (FER), and the HD-ZIP transcription factor member, AtHB7, displayed pronounced expression differences between the cultivars. Notably, our data suggest that following P. cubensis infection, both cultivars suppressed flavonoid biosynthesis via the down-regulation of associated genes whilst concurrently promoting lignin production. The complex interplay of transcriptomic and metabolic responses elucidated by this study provides foundational insights into melon's defense mechanisms against DM. The robust resilience of 'K10-1' to DM is attributed to the synergistic interaction of its inherent transcriptomic and metabolic reactions.

Hydroponic versus soil-based cultivation of sweet basil: impact on plants' susceptibility to downy mildew and heat stress, storability and total antioxidant capacity

BACKGROUND

In recent years, hydroponically cultivated basil has gained extensive popularity over soil-based cultivation. Evidence for potential differences between both cultivation methods, in terms of resistance to biotic and abiotic stress factors, storage properties and shelf-life, is still lacking and the potential effect of cultivation method on the antioxidant capacity has not yet been fully explored. This study aimed to determine which of the two basil cultivation methods produces plants that are more resilient to downy mildew and external heat treatment and that exhibit better storage and shelf-life performance.

RESULTS

Hydroponically grown basil was significantly more affected by browning than the soil-grown basil at the end of the storage and end of the shelf-life period. Under both cultivation methods, the extent of browning increased significantly between the end of the storage and end of the shelf-life period, by a factor of 1.4. Moreover, hydroponically grown plants were significantly more sensitive to heat treatment than soil-grown basil. However, the soil-grown basil exhibited significantly greater susceptibility to downy mildew than the hydroponically grown basil. At harvest, and at the end of the storage period, the antioxidant capacity of hydroponically cultivated basil was significantly greater than that of soil-grown basil.

CONCLUSIONS

Hydroponically cultivated basil exhibited greater resistance to downy mildew, but less resilience to heat and browning during storage and a shelf-life period, resulting in poorer storage and shelf-life performance as compared to soil-cultivated basil. The greater total antioxidant capacity of the hydroponically cultivated basil seems to be the major cause for the observed phenomena. © 2023 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Comparative Transcriptome Analysis between Resistant and Susceptible Pakchoi Cultivars in Response to Downy Mildew

Downy mildew caused by the obligate parasite Hyaloperonospora brassicae is a devastating disease for Brassica species. Infection of Hyaloperonospora brassicae often leads to yellow spots on leaves, which significantly impacts quality and yield of pakchoi. In the present study, we conducted a comparative transcriptome between the resistant and susceptible pakchoi cultivars in response to Hyaloperonospora brassicae infection. A total of 1073 disease-resistance-related differentially expressed genes were identified using a Venn diagram. The Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway analyses revealed that these genes were mainly involved in plant-pathogen interaction, plant hormone signal transduction, and other photosynthesis-related metabolic processes. Analysis of the phytohormone content revealed that salicylic acid increased significantly in the resistant material after inoculation with Hyaloperonospora brassicae, whereas the contents of jasmonic acid, abscisic acid, and 1-aminocyclopropane-1-carboxylic acid decreased. Exogenous salicylic acid treatment also significantly upregulated Hyaloperonospora brassicae-induced genes, which further confirmed a crucial role of salicylic acid during pakchoi defense against Hyaloperonospora brassicae. Based on these findings, we suggest that the salicylic-acid-mediated signal transduction contributes to the resistance of pakchoi to downy mildew, and PAL1, ICS1, NPR1, PR1, PR5, WRKY70, WRKY33, CML43, CNGC9, and CDPK15 were involved in this responsive process. Our findings evidently contribute to revealing the molecular mechanism of pakchoi defense against Hyaloperonospora brassicae.

Additive and synergistic antifungal effects of copper and phenolic extracts from grape cane and apples

BACKGROUND

Organic viticulture seeks sustainable alternatives for eco-toxic copper fungicides to control downy mildew caused by Plasmopara viticola. (Poly)phenol-rich extracts of agricultural byproducts are known to possess antifungal activity, but high production costs often limit their actual implementation.

RESULTS

We developed and produced novel ligninsulfonate-based grape cane extract (GCE) formulations and an apple extract on a pilot plant scale, including a detailed (poly)phenol characterization by high-performance liquid chromatography photodiode array mass spectrometry (HPLC-PDA-MS). Our GCE formulations alone reduced downy mildew disease severity in greenhouse trials by 29%-69% in a dose-dependent manner, whereas a standard application of the copper-based agent alone reached ~56%. When applied together, disease severity was diminished by 78%-92%, revealing a synergistic effect that depended on the mixture ratio. Combining GCE formulations with the apple extract, additive effects were found (80% disease severity reduction).

CONCLUSION

The studied plant extracts are proposed to both substitute for and synergistically reinforce copper fungicides in grapevine downy mildew control. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Fungicide-Saving Potential and Economic Advantages of Fungus-Resistant Grapevine Cultivars

The high susceptibility of European grapevine cultivars to downy mildew (DM) and powdery mildew (PM) causes the intensive use of fungicides. Fungus-resistant cultivars (FRCs) with different resistance (R) loci have been bred and could play an important role in reducing plant protection treatments (PPTs). However, little information is available about the extent to which PPTs can be reduced in the field through the use of FRCs and the associated economic advantages. In this study, different strategies with reduced PPTs on FRCs were tested in field experiments. The results demonstrated that the number of PPTs can be reduced by 60 to 90%, resulting in reductions in applied copper and sulfur by 52 to 79% through the use of FRCs compared with susceptible cultivars, without affecting grape or plant health. The saving potential varied among years, depending on the type of R loci and climatic conditions. Furthermore, this study highlights that completely omitting PPTs in the cultivation of FRCs can result in PM or DM infections and possible loss of yield and fruit quality. In addition to the field experiments, a two-year observation of the performance of FRCs in commercial vineyards was undertaken, which highlighted not only the significant reduction in PPTs but also the financial savings that can be achieved through the use of FRCs.

Simultaneous editing of two DMR6 genes in grapevine results in reduced susceptibility to downy mildew

The reduction of pesticide treatments is of paramount importance for the sustainability of viticulture, and it can be achieved through a combination of strategies, including the cultivation of vines (Vitis vinifera) that are resistant or tolerant to diseases such as downy mildew (DM). In many crops, the knock-out of Downy Mildew Resistant 6 (DMR6) proved successful in controlling DM-resistance, but the effect of mutations in DMR6 genes is not yet known in grapevine. Today, gene editing serves crop improvement with small and specific mutations while maintaining the genetic background of commercially important clones. Moreover, recent technological advances allowed to produce non-transgenic grapevine clones by regeneration of protoplasts edited with the CRISPR/Cas9 ribonucleoprotein. This approach may revolutionize the production of new grapevine varieties and clones, but it requires knowledge about the targets and the impact of editing on plant phenotype and fitness in different cultivars. In this work we generated single and double knock-out mutants by editing DMR6 susceptibility (S) genes using CRISPR/Cas9, and showed that only the combined mutations in VviDMR6-1 and VviDMR6-2 are effective in reducing susceptibility to DM in two table-grape cultivars by increasing the levels of endogenous salicylic acid. Therefore, editing both genes may be necessary for effective DM control in real-world agricultural settings, which could potentially lead to unwanted phenotypes. Additional research, including trials conducted in experimental vineyards, is required to gain a deeper understanding of DMR6-based resistance.

capitata L.)

Hyaloperonospora parasitica is a global pathogen that can cause leaf necrosis and seedling death, severely threatening the quality and yield of cabbage. However, the genome sequence and infection mechanisms of H. parasitica are still unclear. Here, we present the first whole-genome sequence of H. parasitica isolate BJ2020, which causes downy mildew in cabbage. The genome contains 4631 contigs and 9991 protein-coding genes, with a size of 37.10 Mb. The function of 6128 genes has been annotated. We annotated the genome of H. parasitica strain BJ2020 using databases, identifying 2249 PHI-associated genes, 1538 membrane transport proteins, and 126 CAZy-related genes. Comparative analyses between H. parasitica, H.arabidopsidis, and H. brassicae revealed dramatic differences among these three Brassicaceae downy mildew pathogenic fungi. Comprehensive genome-wide clustering analysis of 20 downy mildew-causing pathogens, which infect diverse crops, elucidates the closest phylogenetic affinity between H. parasitica and H. brassicae, the causative agent of downy mildew in Brassica napus. These findings provide important insights into the pathogenic mechanisms and a robust foundation for further investigations into the pathogenesis of H. parasitica BJ2020.

A Bayesian model for control strategy selection against Plasmopara viticola infections

Plant pathogens pose a persistent threat to grape production, causing significant economic losses if disease management strategies are not carefully planned and implemented. Simulation models are one approach to address this challenge because they provide short-term and field-scale disease prediction by incorporating the biological mechanisms of the disease process and the different phenological stages of the vines. In this study, we developed a Bayesian model to predict the probability of Plasmopara viticola infection in grapevines, considering various disease management approaches. To aid decision-making, we introduced a multi-attribute utility function that incorporated a sustainability index for each strategy. The data used in this study were derived from trials conducted during the production years 2018-2020, involving the application of five disease management strategies: conventional Integrated Pest Management (IPM), conventional organic, IPM with substantial fungicide reduction combined with host-defense inducing biostimulants, organic management with biostimulants, and the use of biostimulants only. Two scenarios were considered, one with medium pathogen pressure (Average) and another with high pathogen pressure (Severe). The results indicated that when sustainability indexes were not considered, the conventional IPM strategy provided the most effective disease management in the Average scenario. However, when sustainability indexes were included, the utility values of conventional strategies approached those of reduced fungicide strategies due to their lower environmental impact. In the Severe scenario, the application of biostimulants alone emerged as the most effective strategy. These results suggest that in situations of high disease pressure, the use of conventional strategies effectively combats the disease but at the expense of a greater environmental impact. In contrast to mechanistic-deterministic approaches recently published in the literature, the proposed Bayesian model takes into account the main sources of heterogeneity through the two group-level effects, providing accurate predictions, although precise estimates of random effects may require larger samples than usual. Moreover, the proposed Bayesian model assists the agronomist in selecting the most effective crop protection strategy while accounting for induced environmental side effects through customizable utility functions.

The current status, challenges, and future perspectives for managing diseases of brassicas

The Brassica genus comprises the greatest diversity of agriculturally important crops. Several species from this genus are grown as vegetable and oil crops for food, animal feed and industrial purposes. In particular, B. oleracea has been extensively bred to give rise to several familiar vegetables (cabbage, broccoli, cauliflower, kale and Brussels Sprouts, etc.) that are grouped under seven major cultivars. In 2020, 96.4 million tonnes of vegetable brassicas were produced globally with a 10.6% increase over the past decade. Yet, like other crops, the production of brassicas is challenged by diseases among which, black rot, clubroot, downy mildew and turnip yellows virus have been identified by growers as the most damaging to UK production. In some cases, yield losses can reach 90% depending upon the geographic location of cultivation. This review aims to provide an overview of the key diseases of brassicas and their management practices, with respect to the biology and lifecycle of the causal pathogens. In addition, the existing controls on the market as well as those that are currently in the research and development phases were critically reviewed. There is not one specific control method that is effective against all the diseases. Generally, cultural practices prevent disease rather than reduce or eliminate disease. Chemical controls are limited, have broad-spectrum activity, are damaging to the environment and are rapidly becoming ineffective due to the evolution of resistance mechanisms by the pathogens. It is therefore important to develop integrated pest management (IPM) strategies that are tailored to geographic locations. Several knowledge gaps have been identified and listed in this review along with the future recommendations to control these four major diseases of brassicas. As such, this review paper will act as a guide to sustainably tackle pre-harvest diseases in Brassica crops to reduce food loss.

Variation in Susceptibility to Downy Mildew Infection in Spanish Minority Vine Varieties

Downy mildew is one of the most destructive diseases affecting grapevines (Vitis vinifera L.). Caused by the oomycete Plasmopara viticola (Berk. and Curt.) Berl. and de Toni, it can appear anywhere where vines are cultivated. It is habitually controlled by the application of phytosanitary agents (copper-based or systemic) at different stages of the vine growth cycle. This, however, is costly, can lead to reduced yields, has a considerable environmental impact, and its overuse close to harvest can cause fermentation problems. All grapevines are susceptible to this disease, although the degree of susceptibility differs between varieties. Market demands and European legislation on viticulture and the use of phytosanitary agents (art. 14 of Directive 128/2009/EC) now make it important to know the sensitivity of all available varieties, including minority varieties. Such knowledge allows for a more appropriate use of phytosanitary agents, fosters the commercial use of these varieties and thus increases the offer of wines associated with different terroirs, and helps identify material for use in crop improvement programmes via crossing or genetic transformation, etc. Over 2020-2021, the susceptibility to P. viticola of 63 minority vine varieties from different regions of Spain was examined in the laboratory using the leaf disc technique. Some 87% of these varieties were highly susceptible and 11% moderately susceptible; just 2% showed low susceptibility. The least susceptible of all was the variety Morate (Madrid, IMIDRA). Those showing intermediate susceptibility included the varieties Sanguina (Castilla la Mancha, IVICAM), Planta Mula (Comunidad Valenciana, ITVE), Rayada Melonera (Madrid, IMIDRA), Zamarrica (Galicia, EVEGA), Cariñena Roja (Cataluña, INCAVI), Mandrègue (Aragón, DGA) and Bastardo Blanco (Extremadura, CICYTEX). The highly susceptible varieties could be differentiated into three subgroups depending on sporulation severity and density.

Impact of UV Irradiation on the Chitosan Bioactivity for Biopesticide Applications

Chitosan is known for its antimicrobial and antifungal properties that make it a promising candidate for plant protection. However, when sprayed in open fields, the bioactivity of chitosan significantly diminishes, suggesting a possible influence of sunlight on chitosan structure. This study aimed to investigate the effects of UV radiation, by using artificial UV sources simulating sunlight, on the stability of chitosan. A powdered chitosan with a low polymerization degree was selected and analyzed using various physicochemical methods, both before and after irradiation. Some minor differences appeared. UV spectra analysis revealed the disappearance of initially present chromophores and the emergence of a new band around 340 nm, potentially indicating the formation of carbonyl compounds. However, elemental analysis, MALDI-TOF spectra, polymerization degree, and infrared spectra did not exhibit any clear structural modifications of chitosan. Interestingly, irradiated powdered chitosan samples maintained their bioactivity, including their eliciting and antifungal properties. In the case of grapevine, irradiated chitosan demonstrated effectiveness in controlling grapevine diseases such as downy mildew, contradicting the assumption that sunlight is responsible for the decreased effectiveness of chitosan in open field conditions.

Fine mapping of a novel QTL DM9.1 conferring downy mildew resistance in melon

Downy mildew (DM) is a major foliar disease globally causing great economic loss in melon production. Utilizing disease-resistant cultivars is the most efficient approach for disease control, while discovery of disease-resistant genes is crucial for the success of DM-resistant breeding. To address this problem, two F₂ populations were constructed using the DM-resistant accession PI 442177 in this study, and QTLs conferring DM resistance were mapped using linkage map and QTL-seq analysis, respectively. A high-density genetic map with the length of 1096.7 cM and density of 0.7 cM was generated by using the genotyping-by-sequencing data of a F₂ population. A major QTL DM9.1 with the phenotypic variance explained proportion of 24.3-37.7% was consistently detected at the early, middle, and late growth stages using the genetic map. QTL-seq analyses on the two F₂ populations also validated the presence of DM9.1. Kompetitive Allele-Specific PCR (KASP) assay was further carried out to fine map DM9.1 into 1.0 Mb interval. A KASP marker co-segregating with DM9.1 was successfully developed. These results not only provided valuable information for DM-resistant gene cloning, but also offered useful markers for melon DM-resistant breeding programs.

Identification of Fungicide Combinations Targeting Plasmopara viticola and Botrytis cinerea Fungicide Resistance Using Machine Learning

Downy mildew (caused by Plasmopara viticola) and gray mold (caused by Botrytis cinerea) are fungal diseases that significantly impact grape production globally. Cytochrome b plays a significant role in the mitochondrial respiratory chain of the two fungi that cause these diseases and is a key target for quinone outside inhibitor (QoI)-based fungicide development. Since the mode of action (MOA) of QoI fungicides is restricted to a single active site, the risk of developing resistance to these fungicides is deemed high. Consequently, using a combination of fungicides is considered an effective way to reduce the development of QoI resistance. Currently, there is little information available to help in the selection of appropriate fungicides. This study used a combination of in silico simulations and quantitative structure-activity relationship (QSAR) machine learning algorithms to screen the most potent QoI-based fungicide combinations for wild-type (WT) and the G143A mutation of fungal cytochrome b. Based on in silico studies, mandestrobin emerged as the top binder for both WT Plasmopara viticola and WT Botrytis cinerea cytochrome b. Famoxadone appeared to be a versatile binder for G143A-mutated cytochrome b of both Plasmopara viticola and Botrytis cinerea. Thiram emerged as a reasonable, low-risk non-QoI fungicide that works on WT and G143A-mutated versions of both fungi. QSAR analysis revealed fenpropidin, fenoxanil, and ethaboxam non-QoIs to have a high affinity for G143A-mutated cytochrome b of Plasmopara viticola and Botrytis cinerea. Above-QoI and non-QoI fungicides can be considered for field studies in a fungicide management program against Plasmopara viticola- and Botrytis cinerea-based fungal infections.

Within-Season Shift in Fungicide Sensitivity Profiles of Pseudoperonospora cubensis Populations in Response to Chemical Control

Cucurbit downy mildew, caused by Pseudoperonospora cubensis, is an important disease affecting cucurbits worldwide. Chemical control is an effective method for disease control but P. cubensis has a high risk for developing resistance to fungicides. Alternating fungicides with different modes of action is recommended to avoid an increase of resistant subpopulations. Thus, this study was conducted to establish shifts in the sensitivity profiles of P. cubensis isolates during the growing season, wherein chlorothalonil was applied in alternation with either cymoxanil, fluopicolide, or propamocarb in field experiments conducted from 2018 to 2020 at Rocky Mount, NC and in 2018 and 2020 at Charleston, SC. The sensitivity of baseline isolates sampled early in the season or exposed isolates sampled late in the season to these single-site fungicides was determined using a detached-leaf assay, where tested isolates were classified as sensitive or resistant based on the relative disease severity. Based on the Kruskal-Wallis test, the distribution profile of relative disease severity among baseline and exposed isolates was significantly different where chlorothalonil was alternated with fluopicolide (χ² = 10.82; P = 0.001) but not with cymoxanil (χ² = 1.39; P = 0.238) or propamocarb (χ² = 2.37; P = 0.412). Although there was a directional selection toward resistance for isolates sampled from plots that were treated with fluopicolide or propamocarb alternated with chlorothalonil during a growing season, a significant shift in fungicide sensitivity distribution based on combined data were observed for fluopicolide (χ² = 8.25; P = 0.004) but not propamocarb (χ² = 1.05; P = 0.461). Baseline and exposed isolates sampled from the cymoxanil-treated plots were all resistant to this fungicide and there was no significant shift in their fungicide sensitivity profile during a growing season (χ² = 0.06; P = 1.000). These results indicate that a shift toward reduced sensitivity in P. cubensis can occur during a growing season and the efficacy of fluopicolide is likely to decrease as the frequency of the less sensitive subpopulations increases during a production season. The resultant effect on disease severity and selection of an insensitive subpopulation may accelerate the development of resistance to propamocarb in the southeastern United States.

Past, present, and future of genetic strategies to control tolerance to the main fungal and oomycete pathogens of grapevine

The production of high-quality wines is strictly related to the correct management of the vineyard, which guarantees good yields and grapes with the right characteristics required for subsequent vinification. Winegrowers face a variety of challenges during the grapevine cultivation cycle: the most notorious are fungal and oomycete diseases such as downy mildew, powdery mildew, and gray mold. If not properly addressed, these diseases can irremediably compromise the harvest, with disastrous consequences for the production and wine economy. Conventional defense methods used in the past involved chemical pesticides. However, such approaches are in conflict with the growing attention to environmental sustainability and shifts from the uncontrolled use of chemicals to the use of integrated approaches for crop protection. Improvements in genetic knowledge and the availability of novel biotechnologies have created new scenarios for possibly producing grapes with a reduced, if not almost zero, impact. Here, the main approaches used to protect grapevines from fungal and oomycete diseases are reviewed, starting from conventional breeding, which allowed the establishment of new resistant varieties, followed by biotechnological methods, such as transgenesis, cisgenesis, intragenesis, and genome editing, and ending with more recent perspectives concerning the application of new products based on RNAi technology. Evidence of their effectiveness, as well as potential risks and limitations based on the current legislative situation, are critically discussed.

Characterization of Italian Plasmopara viticola populations for resistance to oxathiapiprolin

BACKGROUND

Oxathiapiprolin is a novel fungicide and the first of the piperidinyl-thiazole-isoxazoline class to be discovered. This fungicide has been reported to have high activity against Plasmopara viticola, the grapevine downy mildew agent, and other plant-pathogenic oomycetes. In this study, the baseline sensitivity of Italian P. viticola populations towards oxathiapiprolin was established on 29 samples collected in 10 different viticultural areas. Two insensitive strains were characterized for their mechanism of resistance.

RESULTS

Oxathiapiprolin exhibited substantial inhibitory activity against 27 of the 29 populations tested, with EC₅₀ values ranging from a minimum of under 4 × 10^-5  mg L^-1 to over 4 × 10^-1  mg L^-1 , with an average value of 3.2 × 10^-2  mg L^-1 . Two stable suspected oxathiapiprolin-resistant mutants were isolated from population exhibiting reduced sensitivity, and sequenced for the oxathiapiprolin target gene PvORP1. The comparison with wild-type isolates revealed that the resistant isolates possessed a heterozygous mutation causing the amino acid substitution N837I, recently reported in the literature.

CONCLUSION

The results obtained indicate a risk for Italian P. viticola populations to develop resistance to oxathiapiprolin in association with the N837I mutation at PvORP1. Anti-resistance strategies should be carefully implemented and the sensitivity levels to this molecule should be monitored accurately in future to preserve its effectiveness. © 2022 Society of Chemical Industry.

Diketopiperazine cyclo(-l-Leu-l-Phe) with plant elicitation activity and anti-oomycete activity against Plasmopara viticola

The aim of this study was to contribute to the reduction of synthetic chemical fungicide application in viticulture by using cyclo(-l-Leu-l-Phe) (cLF) produced by Bacillus subtilis KS1, a candidate for biological control agent. cLF is a diketopiperazine and belongs to the family of 2,5-diketopiperazines. KS1 secreted micromolar levels of cLF into culture medium. Micromolar concentrations of cLF structure-dependently decreased by ∼90% both disease severity and lesion density of downy mildew in grapevine cultivated in a growth chamber. Microscopic observation demonstrated that cLF inhibited Plasmopara viticola haustorium formation by 80% but not zoospore germination on leas disks. Interestingly, millimolar concentrations of cLF induced plant defense response, such as expression of genes encoding chitinase and β-1,3-glucanase, in grapevine leaves through the salicylic acid and jasmonate signaling pathways. We demonstrated that cLF was a weapon against P. viticola infection. Further evaluation of cLF in field trials is required to uncover its inherent characteristics.

viticola Pathovar

Vitis vinifera L. is highly susceptible to the biotrophic pathogen Plasmopara viticola. To control the downy mildew disease, several phytochemicals are applied every season. Recent European Union requirements to reduce the use of chemicals in viticulture have made it crucial to use alternative and more sustainable approaches to control this disease. Our previous studies pinpoint the role of fatty acids and lipid signalling in the establishment of an incompatible interaction between grapevine and P. viticola. To further understand the mechanisms behind lipid involvement in an effective defence response we have analysed the expression of several genes related to lipid metabolism in three grapevine genotypes: Chardonnay (susceptible); Regent (tolerant), harbouring an Rpv3-1 resistance loci; and Sauvignac (resistant) that harbours a pyramid of Rpv12 and Rpv3-1 resistance loci. A highly aggressive P. viticola isolate was used (NW-10/16). Moreover, we have characterised the grapevine phospholipases C and D gene families and monitored fatty acid modulation during infection. Our results indicate that both susceptible and resistant grapevine hosts did not present wide fatty acid or gene expression modulation. The modulation of genes associated with lipid signalling and fatty acids seems to be specific to Regent, which raises the hypothesis of being specifically linked to the Rpv3 loci. In Sauvignac, the Rpv12 may be dominant concerning the defence response, and, thus, this genotype may present the activation of other pathways rather than lipid signalling.

Croatian Native Grapevine Varieties' VOCs Responses upon Plasmopara viticola Inoculation

The Plasmopara viticola pathogen causes one of the most severe grapevine diseases, namely downy mildew. The response to P. viticola involves both visible symptoms and intricate metabolomic alterations, particularly in relation to volatile organic compounds, and depends on the degree of resistance of a particular variety. There are numerous native grapevine varieties in Croatia, and they vary in susceptibility to this oomycete. As previously reported, in vitro leaf disc bioassay and polyphenolic compound analysis are complementary methods that can be used to separate native varieties into various resistance classes. This research used the Solid Phase Microextraction-Arrow Gas Chromatography-Mass Spectrometry method to identify the early alterations in the VOCs in the leaves after P. viticola inoculation. Based on the absolute peak area of sesquiterpenes, some discrepancies between the sampling terms were noticed. The presence of certain chemical compounds such as humulene, ylangene, and α-farnesene helped distinguish the non-inoculated and inoculated samples. Although specific VOC responses to P. viticola infection of native varieties from various resistance classes could not be identified, the response of less susceptible native varieties and resistant controls was associated with an increase in the absolute peak area of several compounds, including geranylacetone, ß-ocimene, and (E)-2-hexen-1-ol.

Disease Forecasting for the Rational Management of Grapevine Mildews in the Chianti Bio-District (Tuscany)

Downy and powdery mildews are major grapevine diseases. In organic viticulture, a few fungicides with protectant activities (copper and sulphur in particular) can be used, and their preventative application frequently leads to unneeded spraying. The adoption of an epidemiological disease forecasting model could optimise the timing of treatments and achieve a good level of disease protection. In this study, the effectiveness of the EPI (Etat Potentiel d'Infection) model in predicting infection risk for downy and powdery mildews was evaluated in nine organic vineyards located in Panzano in Chianti (FI), over a 2-year period (2020-2021). The reliability of the EPI model was investigated by comparing the disease intensities, the number of fungicide sprayings, the quantities of the fungicides (kg/ha), and the costs of the treatment achieved, with or without the use of the model, in a vineyard. The results obtained over two seasons indicated that, in most cases, the use of the EPI model accurately signalled the infection risk and allowed for a reduction in the frequency and cost of spraying, particularly for powdery mildew control (-40% sprayings, -20% costs compared to the farmer's schedule), without compromising crop protection. The use of the EPI model can, therefore, contribute to more-sustainable disease management in organic viticulture.

Current Trends and Perspectives on Predictive Models for Mildew Diseases in Vineyards

Environmental and economic costs demand a rapid transition to more sustainable farming systems, which are still heavily dependent on chemicals for crop protection. Despite their widespread application, powdery mildew (PM) and downy mildew (DM) continue to generate serious economic penalties for grape and wine production. To reduce these losses and minimize environmental impacts, it is important to predict infections with high confidence and accuracy, allowing timely and efficient intervention. This review provides an appraisal of the predictive tools for PM and DM in a vineyard, a specialized farming system characterized by high crop protection cost and increasing adoption of precision agriculture techniques. Different methodological approaches, from traditional mechanistic or statistic models to machine and deep learning, are outlined with their main features, potential, and constraints. Our analysis indicated that strategies are being continuously developed to achieve the required goals of ease of monitoring and timely prediction of diseases. We also discuss that scientific and technological advances (e.g., in weather data, omics, digital solutions, sensing devices, data science) still need to be fully harnessed, not only for modelling plant-pathogen interaction but also to develop novel, integrated, and robust predictive systems and related applied technologies. We conclude by identifying key challenges and perspectives for predictive modelling of phytopathogenic disease in vineyards.

Fine Mapping and Identification of a Candidate Gene of Downy Mildew Resistance, RPF2, in Spinach (Spinacia oleracea L.)

Downy mildew is a major threat to the economic value of spinach. The most effective approach to managing spinach downy mildew is breeding cultivars with resistance genes. The resistance allele RPF2 is effective against races 1-10 and 15 of Peronospora farinosa f. sp. Spinaciae (P. effusa) and is widely used as a resistance gene. However, the gene and the linked marker of RPF2 remain unclear, which limit its utilization. Herein, we located the RPF2 gene in a 0.61 Mb region using a BC₁ population derived from Sp39 (rr) and Sp62 (RR) cultivars via kompetitive allele specific PCR (KASP) markers. Within this region, only one R gene, Spo12821, was identified based on annotation information. The amino acid sequence analysis showed that there were large differences in the length of the LRR domain between the parents. Additionally, a molecular marker, RPF2-IN12821, was developed based on the sequence variation in the Spo12821, and the evaluation in the BC₁ population produced a 100% match with resistance/susceptibility. The finding of the study could be valuable for improving our understanding of the genetic basis of resistance against the downy mildew pathogen and breeding resistance lines in the future.

Spatial Genetic Structure and Pathogenic Race Composition at the Field Scale in the Sunflower Downy Mildew Pathogen, Plasmopara halstedii

Yield losses in sunflower crops caused by Plasmopara halstedii can be up to 100%, depending on the cultivar susceptibility, environmental conditions, and virulence of the pathogen population. The aim of this study was to investigate the genetic and phenotypic structure of a sunflower downy mildew agent at the field scale. The genetic diversity of 250 P. halstedii isolates collected from one field in southern France was assessed using single-nucleotide polymorphisms (SNPs) and single sequence repeats (SSR). A total of 109 multilocus genotypes (MLG) were identified among the 250 isolates collected in the field. Four genotypes were repeated more than 20 times and spatially spread over the field. Estimates of genetic relationships among P. halstedii isolates using principal component analysis and a Bayesian clustering approach demonstrated that the isolates are grouped into two main genetic clusters. A high level of genetic differentiation among clusters was detected (F_ST = 0.35), indicating overall limited exchange between them, but our results also suggest that recombination between individuals of these groups is not rare. Genetic clusters were highly related to pathotypes, as previously described for this pathogen species. Eight different races were identified (100, 300, 304, 307, 703, 704, 707, and 714), with race 304 being predominant and present at most of the sites. The co-existence of multiple races at the field level is a new finding that could have important implications for the management of sunflower downy mildew. These data provide the first population-wide picture of the genetic structure of P. halstedii at a fine spatial scale.

whale by low coverage whole genome sequencing

Spinach (Spinacia oleracea) is a popular leafy vegetable crop and commercial production is centered in California and Arizona in the US. The oomycete Peronospora effusa causes the most important disease in spinach, downy mildew. A total of nineteen races of P. effusa are known, with more than 15 documented in the last three decades, and the regular emergence of new races is continually overcoming the genetic resistance to the pathogen. This study aimed to finely map the downy mildew resistance locus RPF3 in spinach, identify single nucleotide polymorphism (SNP) markers associated with the resistance, refine the candidate genes responsible for the resistance, and evaluate the prediction performance using multiple machine learning genomic prediction (GP) methods. Segregating progeny population developed from a cross of resistant cultivar Whale and susceptible cultivar Viroflay to race 5 of P. effusa was inoculated under greenhouse conditions to determine downy mildew disease response across the panel. The progeny panel and the parents were resequenced at low coverage (1x) to identify genome wide SNP markers. Association analysis was performed using disease response phenotype data and SNP markers in TASSEL, GAPIT, and GENESIS programs and mapped the race 5 resistance loci (RPF3) to 1.25 and 2.73 Mb of Monoe-Viroflay chromosome 3 with the associated SNP in the 1.25 Mb region was 0.9 Kb from the NBS-LRR gene SOV3g001250. The RPF3 locus in the 1.22-1.23 Mb region of Sp75 chromosome 3 is 2.41-3.65 Kb from the gene Spo12821 annotated as NBS-LRR disease resistance protein. This study extended our understanding of the genetic basis of downy mildew resistance in spinach cultivar Whale and mapped the RPF3 resistance loci close to the NBS-LRR gene providing a target to pursue functional validation. Three SNP markers efficiently selected resistance based on multiple genomic selection (GS) models. The results from this study have added new genomic resources, generated an informed basis of the RPF3 locus resistant to spinach downy mildew pathogen, and developed markers and prediction methods to select resistant lines.

Deep semantic segmentation for the quantification of grape foliar diseases in the vineyard

Plant disease evaluation is crucial to pathogen management and plant breeding. Human field scouting has been widely used to monitor disease progress and provide qualitative and quantitative evaluation, which is costly, laborious, subjective, and often imprecise. To improve disease evaluation accuracy, throughput, and objectiveness, an image-based approach with a deep learning-based analysis pipeline was developed to calculate infection severity of grape foliar diseases. The image-based approach used a ground imaging system for field data acquisition, consisting of a custom stereo camera with strobe light for consistent illumination and real time kinematic (RTK) GPS for accurate localization. The deep learning-based pipeline used the hierarchical multiscale attention semantic segmentation (HMASS) model for disease infection segmentation, color filtering for grapevine canopy segmentation, and depth and location information for effective region masking. The resultant infection, canopy, and effective region masks were used to calculate the severity rate of disease infections in an image sequence collected in a given unit (e.g., grapevine panel). Fungicide trials for grape downy mildew (DM) and powdery mildew (PM) were used as case studies to evaluate the developed approach and pipeline. Experimental results showed that the HMASS model achieved acceptable to good segmentation accuracy of DM (mIoU > 0.84) and PM (mIoU > 0.74) infections in testing images, demonstrating the model capability for symptomatic disease segmentation. With the consistent image quality and multimodal metadata provided by the imaging system, the color filter and overlapping region removal could accurately and reliably segment grapevine canopies and identify repeatedly imaged regions between consecutive image frames, leading to critical information for infection severity calculation. Image-derived severity rates were highly correlated (r > 0.95) with human-assessed values, and had comparable statistical power in differentiating fungicide treatment efficacy in both case studies. Therefore, the developed approach and pipeline can be used as an effective and efficient tool to quantify the severity of foliar disease infections, enabling objective, high-throughput disease evaluation for fungicide trial evaluation, genetic mapping, and breeding programs.

Influence on grape aromatic compounds of natural fungicides used for the control of downy mildew

BACKGROUND

The grape volatile fraction determines to a great extent its aroma, which is one of the most important characteristics influencing wine quality and consumer preferences. Grapevine downy mildew (GDM) is one of the most important and devastating diseases of grapevines worldwide. In this study, the impact on the volatile composition of cv. Verdicchio grapes of classical copper formulations, was compared to that of alternative products. Thus, 11 treatments were foliar applied throughout one grapevine cycle.

RESULTS

Most of the volatile compounds present in the grapes were not affected by the treatments used in order to prevent GDM. In the case of the total C₁₃ norisoprenoids, some differences were found between grapes untreated control and those applied with the grapefruit seed extract. Moreover, the content of alcohols was smaller in grapes from Bordeaux mixture treatment and higher in the samples from chitosan application.

CONCLUSION

Therefore, from the qualitative point of view of the berry, treatment with tested products alternative to copper is recommended, which minimize the environmental and health problems that this heavy metal brings to the soil and in the winery, since it means that their applications did not affect the grape aroma. © 2022 Society of Chemical Industry.

A pH- and redox-stimulated responsive hollow mesoporous silica for triggered delivery of fungicides to control downy mildew of Luffa cylindrica

BACKGROUND

Downy mildew, a devastating disease of cucurbitaceous crops caused by Pseudoperonospora cubensis. Although a variety of fungicides are used to control downy mildew, choosing an effective product can be challenging. Environmental stimulus-responsive pesticide delivery systems have great potential to improve the effectiveness of disease and pest control and reduce the impact on environmentally beneficial organisms.

RESULTS

In this work, a disulfide bond (SS)-modified and chitosan oligosaccharide (COS)-capped hollow mesoporous silica (HMS) pesticide delivery system was synthesized using a hard template method for the control of downy mildew in cucurbit crops. The synthesized nanoparticles were loaded with dimethomorph (DMM), denoted as DMM@HMS-SS-COS, and the developmental toxicity of these nanoparticles to zebrafish embryos were evaluated. The results showed that the prepared DMM@HMS-SS-COS exhibited excellent dual response properties to pH and glutathione (GSH), with an encapsulation rate of up to 24.36%. DMM@HMS-SS-COS has good ultraviolet (UV) radiation stability and adhesion properties. Compared with dimethomorph suspension concentrate (SC), DMM@HMS-SS-COS was more effective against downy mildew for up to 21 days. Toxicity tests showed that DMM@HMS-SS-COS significantly reduced the effect of DMM on the hatching rate and survival rate of zebrafish embryos.

CONCLUSIONS

This work not only demonstrates that DMM@HMS-SS-COS could be used as a nanodelivery system for intelligent control of downy mildew but also emphasizes the necessity of increasing the acute toxicity of nanoformulations to non-target organisms in environmental risk assessment. © 2022 Society of Chemical Industry.

Trichoderma species isolated from grapevine with tolerance towards common copper fungicides used in viticulture for plant protection

BACKGROUND

Copper-containing fungicides are applied broadly in organic viticulture against downy mildew caused by Plasmopara viticola. Although long-term application of copper-based fungicides is associated with ecotoxic effects on the environment, their use in viticulture is required until sustainable alternatives are available. Trichoderma spp. might be a promising approach to fungicide reduction while promoting plant growth and development and displaying biocontrol activity. This study aims to examine the tolerance and compatibility of Trichoderma spp. to copper fungicides. This work contributes to the development of a spray application consisting of a copper-tolerant Trichoderma sp. combined with a downscaled copper fungicide rate against P. viticola.

RESULTS

Trichoderma spp. isolated from grapevine wood in vineyards were identified and used for tolerance screening in various concentrations of copper fungicides. Copper hydroxide was identified as being highly compatible with Trichoderma. Two Trichoderma candidates, T. koningiopsis and T. harzianum, showed high copper tolerance in mycelial growth and germination tests, and were adapted to 2.85 g Cu L^-1 of the selected fungicide. Microscopic investigations showed the attachment of copper compounds to fungal cell walls and copper uptake within the cytoplasm. In the case of high tolerance, large-scale copper uptake was prevented.

CONCLUSION

Our findings identified two highly copper-tolerant Trichoderma isolates with natural adaptation to the vineyard ecosystem, which could be further tested as biostimulants and biocontrol agents, combined with a reduced fungicide rate for sustainable plant protection. © 2022 Society of Chemical Industry.

Pathogenesis of Plasmopara viticola Depending on Resistance Mediated by Rpv3_1, and Rpv10 and Rpv3_3, and by the Vitality of Leaf Tissue

Grapevine cultivars vary in their resistance to Plasmopara viticola, causal agent of downy mildew. Genes from various Vitis species confer pathogen resistance (Rpv), resulting in reduced compatibility of the host-pathogen interaction and partial disease resistance that may become apparent at different stages of pathogenesis. This study describes the pathogenesis of P. viticola on the partially resistant cultivars Regent (Rpv3-1) and Solaris (Rpv3-3, Rpv10) as compared with the susceptible cultivar Mueller-Thurgau using various microscopic techniques, visual disease rating as well as qPCR. Host plant resistance had no effect on the initial steps of pathogenesis outside the host plant cells (zoospore attachment, formation of substomatal vesicle) and became detectable only after the formation of primary haustoria. The restricted compatibility resulted in reductions in haustorium size and in the number of secondary haustoria and was associated with callose depositions around haustoria and stomatal guard cells, collapsed mesophyll cells (hypersensitive reaction), and additional production of an amorphous substance in the intercellular space of cultivar Solaris. Resistance mechanisms reduced the efficiency of P. viticola haustoria and largely restricted tissue colonization to the spongy parenchyma; resistance of cultivar Solaris having thicker leaves was more effective than that of cultivar Regent. Despite of the effects of resistance genes, P. viticola was able to complete its life cycle by forming sporangiophores with sporangia through the stomata on both resistant cultivars indicating partial resistance. Differences in the pathogenesis on detached and attached grapevine leaves highlighted the impact of host tissue vitality on both resistance and susceptibility to the biotrophic pathogen.

Genome-Wide Association Analysis of Resistance to Pseudoperonospora cubensis in Citron Watermelon

Cultivated sweet watermelon (Citrullus lanatus) is an important vegetable crop for millions of people around the world. There are limited sources of resistance to economically important diseases within C. lanatus, whereas C. amarus has a reservoir of traits that can be exploited to improve C. lanatus for resistance to biotic and abiotic stresses. Cucurbit downy mildew (CDM), caused by Pseudoperonospora cubensis, is an emerging threat to watermelon production. We screened 122 C. amarus accessions for resistance to CDM over two tests (environments). The accessions were genotyped by whole-genome resequencing to generate 2,126,759 single nucleotide polymorphic (SNP) markers. A genome-wide association study was deployed to uncover marker-trait associations and identify candidate genes underlying resistance to CDM. Our results indicate the presence of wide phenotypic variability (1.1 to 57.8%) for leaf area infection, representing a 50.7-fold variation for CDM resistance across the C. amarus germplasm collection. Broad-sense heritability estimate was 0.55, implying the presence of moderate genetic effects for resistance to CDM. The peak SNP markers associated with resistance to P. cubensis were located on chromosomes Ca03, Ca05, Ca07, and Ca11. The significant SNP markers accounted for up to 30% of the phenotypic variation and were associated with promising candidate genes encoding leucine-rich repeat receptor-like protein kinase and the WRKY transcription factor. This information will be useful in understanding the genetic architecture of the P. cubensis-Citrullus spp. patho-system as well as development of resources for genomics-assisted breeding for resistance to CDM in watermelon.

A jacalin-like lectin domain-containing protein of Sclerospora graminicola acts as an apoplastic virulence effector in plant-oomycete interactions

The plant extracellular space, including the apoplast and plasma membrane, is the initial site of plant-pathogen interactions. Pathogens deliver numerous secreted proteins, called effectors, into this region to suppress plant immunity and establish infection. Downy mildew caused by the oomycete pathogen Sclerospora graminicola (Sg) is an economically important disease of Poaceae crops including foxtail millet (Setaria italica). We previously reported the genome sequence of Sg and showed that the jacalin-related lectin (JRL) gene family has significantly expanded in this lineage. However, the biological functions of JRL proteins remained unknown. Here, we show that JRL from Sg (SgJRL) functions as an apoplastic virulence effector. We identified eight SgJRLs by protein mass spectrometry analysis of extracellular fluid from Sg-inoculated foxtail millet leaves. SgJRLs consist of a jacalin-like lectin domain and an N-terminal putative secretion signal; SgJRL expression is induced by Sg infection. Heterologous expression of three SgJRLs with N-terminal secretion signal peptides in Nicotiana benthamiana enhanced the virulence of the pathogen Phytophthora palmivora inoculated onto the same leaves. Of the three SgJRLs, SG06536 fused with green fluorescent protein (GFP) localized to the apoplastic space in N. benthamiana leaves. INF1-mediated induction of defence-related genes was suppressed by co-expression of SG06536-GFP. These findings suggest that JRLs are novel apoplastic effectors that contribute to pathogenicity by suppressing plant defence responses.

Plasmopara viticola the Causal Agent of Downy Mildew of Grapevine: From Its Taxonomy to Disease Management

Plasmopara viticola (P. viticola, Berk. & M. A. Curtis; Berl. & De Toni) causing grapevine downy mildew is one of the most damaging pathogens to viticulture worldwide. Since its recognition in the middle of nineteenth century, this disease has spread from America to Europe and then to all grapevine-growing countries, leading to significant economic losses due to the lack of efficient disease control. In 1885 copper was found to suppress many pathogens, and is still the most effective way to control downy mildews. During the twentieth century, contact and penetrating single-site fungicides have been developed for use against plant pathogens including downy mildews, but wide application has led to the appearance of pathogenic strains resistant to these treatments. Additionally, due to the negative environmental impact of chemical pesticides, the European Union restricted their use, triggering a rush to develop alternative tools such as resistant cultivars breeding, creation of new active ingredients, search for natural products and biocontrol agents that can be applied alone or in combination to kill the pathogen or mitigate its effect. This review summarizes data about the history, distribution, epidemiology, taxonomy, morphology, reproduction and infection mechanisms, symptoms, host-pathogen interactions, host resistance and control of the P. viticola, with a focus on sustainable methods, especially the use of biocontrol agents.

[Cucumber downy mildew and the mechanisms of host resistance: a review]

The cultivation and production of cucumber are seriously affected by downy mildew caused by Pseudoperonospora cubensis. Downy mildew damages leaves, stems and inflorescences, and then reduces the yield and quality of cucumber. This review summarized the research advances in cucumber downy mildew, including pathogen detection and defense pathways, regulatory factors, mining of pathogens-resistant candidate genes, proteomic and genomic analysis, and development of QTL remarks. This review may facilitate clarifying the resistance mechanisms of cucumber to downy mildew.

Research Advances in Genetic Mechanisms of Major Cucumber Diseases Resistance

Cucumber (Cucumis sativus L.) is an important economic vegetable crop worldwide that is susceptible to various common pathogens, including powdery mildew (PM), downy mildew (DM), and Fusarium wilt (FM). In cucumber breeding programs, identifying disease resistance and related molecular markers is generally a top priority. PM, DM, and FW are the major diseases of cucumber in China that cause severe yield losses and the genetic-based cucumber resistance against these diseases has been developed over the last decade. Still, the molecular mechanisms of cucumber disease resistance remain unclear. In this review, we summarize recent findings on the inheritance, molecular markers, and quantitative trait locus mapping of cucumber PM, DM, and FM resistance. In addition, several candidate genes, such as PM, DM, and FM resistance genes, with or without functional verification are reviewed. The data help to reveal the molecular mechanisms of cucumber disease resistance and provide exciting new opportunities for further resistance breeding.

Transcriptional Profiling of Resistant and Susceptible Cultivars of Grapevine (Vitis L.) Reveals Hypersensitive Responses to Plasmopara viticola

Grapevine downy mildew is the most serious disease of grapevine cultivars that affects the rate of resistance/susceptibility to Plasmopara viticola. In this study, we used the susceptible cultivar "Zitian Seedless" and the resistant cultivar "Kober 5BB" as materials to determine the transcriptome differences and phenotypes of the leaves after inoculation with downy mildew. The differences in microstructures and molecular levels were compared and analyzed. Fluorescence staining and microscopic observations confirmed that hypersensitive cell death occurred around the stomata in "Kober 5BB" infected by downy mildew zoospores. Meanwhile, transcriptomic profiling indicated that there were 11,713 and 6,997 gene expression differences between the resistant and susceptible cultivars at 72 h after inoculation when compared to control (0 h), respectively. The differentially expressed genes of the two cultivars are significantly enriched in different pathways, including response to plant-pathogen interaction, mitogen-activated protein kinase (MAPK) signaling pathway, plant hormone signal transduction, phenylpropanoid, and flavonoid biosynthesis. Furthermore, the results of functional enrichment analysis showed that H₂O₂ metabolism, cell death, reactive oxygen response, and carbohydrate metabolism are also involved in the defense response of "Kober 5BB," wherein a total of 322 key genes have been identified. The protein interaction network showed that metacaspases (MCAs), vacuolar processing enzymes (VPEs), and Papain-like cysteine proteases (PLCPs) play an important role in the execution of hypersensitive responses (HR). In conclusion, we demonstrated that HR cell death is the key strategy in the process of grape defense against downy mildew, which may be mediated or activated by Caspase-like proteases.

Design, synthesis, and fungicidal activity of novel N-substituted piperazine-containing phenylpyridines against cucumber downy mildew

BACKGROUND

Cucumber downy mildew (CDM) is a severe plant disease and affects the yield of cucumber production worldwide. As the resistance toward conventional fungicides is emerging as a ubiquitous issue, it is urgent to discover efficient fungicides with unique structures.

RESULTS

In this study, a series of novel phenylpyridine derivatives were designed and synthesized. Bioassays revealed that most of these compounds possessed excellent fungicidal activities against CDM. Among the phenylpyridine compounds, 2-(4-(4-(tert-butyl)benzyl)piperazin-1-yl)-6-phenylnicotinonitrile (C8) [half-maximal effective concentration (EC₅₀ ) = 4.40 mg L^-1 ] displayed the highest activity, which was better than those of the commercial fungicides, such as azoxystrobin (EC₅₀  = 42.77 mg L^-1 ) and flumorph (EC₅₀  = 41.94 mg L^-1 ). Furthermore, the molecular electrostatic potential of high-activity compound C8 indicated that nitrogen atom of the cyano group on the pyridine ring was in the negative region and may easily form hydrogen bonds and allow for electrostatic interactions with potential receptors.

CONCLUSIONS

This study demonstrated that the novel N-substituted piperazine-containing phenylpyridine derivatives could be further developed as a candidate compound to control CDM.

Unraveling the Genetic Basis of Key Agronomic Traits of Wrinkled Vining Pea (Pisum sativum L.) for Sustainable Production

Estimating the allelic variation and exploring the genetic basis of quantitatively inherited complex traits are the two foremost breeding scenarios for sustainable crop production. The current study utilized 188 wrinkled vining pea genotypes comprising historical varieties and breeding lines to evaluate the existing genetic diversity and to detect molecular markers associated with traits relevant to vining pea production, such as wrinkled vining pea yield (YTM100), plant height (PH), earliness (ERL), adult plant resistance to downy mildew (DM), pod length (PDL), numbers of pods per plant (PDP), number of peas per pod (PPD), and percent of small wrinkled vining peas (PSP). Marker-trait associations (MTAs) were conducted using 6902 quality single nucleotide polymorphism (SNP) markers generated from the diversity arrays technology sequencing (DArTseq) and Genotyping-by-sequencing (GBS) sequencing methods. The best linear unbiased prediction (BLUP) values were estimated from the two-decades-long (1999-2020) unbalanced phenotypic data sets recorded from two private breeding programs, the Findus and the Birds eye, now owned by Nomad Foods. Analysis of variance revealed a highly significant variation between genotypes and genotype-by-environment interactions for the ten traits. The genetic diversity and population structure analyses estimated an intermediate level of genetic variation with two optimal sub-groups within the current panel. A total of 48 significant (P < 0.0001) MTAs were identified for eight different traits, including five for wrinkled vining pea yield on chr2LG1, chr4LG4, chr7LG7, and scaffolds (two), and six for adult plant resistance to downy mildew on chr1LG6, chr3LG5 (two), chr6LG2, and chr7LG7 (two). We reported several novel MTAs for different crucial traits with agronomic importance in wrinkled vining pea production for the first time, and these candidate markers could be easily validated and integrated into the active breeding programs for marker-assisted selection.

Leaf Polyphenolic Profile as a Determinant of Croatian Native Grapevine Varieties' Susceptibility to Plasmopara viticola

Since grapevine is highly susceptible to various pathogens, enormous amounts of pesticides are applied each season to achieve profitable production. One of the most destructive grapevine diseases is downy mildew, and their interaction has been in the spotlight for more than a decade. When it comes to a metabolome level, phenolic compounds are relevant to investigate due to their involvement in the plant immune system and known antifungal properties. Croatian grapevine germplasm is highly heterogeneous due to its long history of cultivation in diversified geographical regions. Since it has been found that native varieties react differently to the infection of Plasmopara viticola, the intention of this study is to define if the chemical background of the leaves, i.e., polyphenolic composition, is responsible for these dissimilarities. Therefore, the leaves of 17 genotypes, among which 14 were native and 3 were controls, were analyzed using high-performance liquid chromatography (HPLC) in four terms: before inoculation and 24, 48, and 96 h post inoculation (hpi). During this early phase, significant differences were found neither between the terms nor between the non-inoculated and inoculated samples, except for resveratrol-3-O-glucoside. By applying principal component analysis (PCA) using initial leaf polyphenolic composition, varieties of V. vinifera were clearly separated into three different groups corresponding to their International Organization of Vine and Wine (OIV) classes of susceptibility to P. viticola. Results obtained in this research suggest that the initial constitutive polyphenolic composition of the cultivar leaves has a crucial influence on their susceptibility to P. viticola, and this finding can be used to improve the success of grapevine breeding programs toward downy mildew resistance.

Evaluation of Disease Severity and Molecular Relationships Between Peronospora variabilis Isolates on Chenopodium Species in New Hampshire

Quinoa is a potential new crop for New England; however, its susceptibility to downy mildew, caused by Peronospora variabilis, is a key obstacle for cultivation. The objectives of this study were to evaluate differential resistance within the Chenopodium genus, identify novel sources of resistance for use in future genetic studies or breeding programs, and investigate phylogenetic relationships of P. variabilis isolates from different Chenopodium hosts. The long-term goal of this research is to develop a resistant variety of quinoa to be grown in New England. Field trials conducted at the University of New Hampshire evaluated downy mildew disease severity on 10 Chenopodium accessions representing four species. Disease severity for each treatment was compared and significant differences in disease severity were observed between accessions. C. berlandieri var. macrocalycium ecotypes collected from Rye Beach, New Hampshire and Appledore Island, Maine exhibited the lowest disease severity over the growing season. P. variabilis was isolated from each accession, and COX2 sequences were compared. Phylogenetic analyses suggest no effect of host species on P. variabilis sequence similarity; however, isolates are shown to cluster by geographic location. This research provides the first step in identifying potential New England native sources of resistance to downy mildew within the genus Chenopodium and provides preliminary information needed to further investigate resistance at the genomic level in Chenopodium spp.

Mitochondrial Loci Enable Specific Quantitative Real-Time PCR Detection of the Pathogen Causing Contemporary Impatiens Downy Mildew Epidemics

Impatiens downy mildew (IDM) disease is a primary constraint on the production of Impatiens walleriana, a popular and economically important floriculture plant. IDM is caused by the biotrophic. oomycete Plasmopara destructor that emerged as a pathogen of I. walleriana in the 2000s. To enable P. destructor detection and quantification, a hydrolysis-probe-based quantitative PCR diagnostic assay was developed based on unique orientation and order of the mitochondrial cytochrome c oxidase subunit1 (cox1) and ATP synthase subunit alpha (atp1) genes in the genus Plasmopara. Nucleotide sequences and analysis of the cox1/atp1 region distinguished P. destructor and its sister-species P. obducens, consistent with prior phylogenetic analyses using cox2 and rDNA markers. Specificity for P. destructor was incorporated into a hydrolysis probe targeting the cox1 gene and flanking primers that amplified across the cox1/atp1 intergenic region. The limit of detection was 0.5 fg/μl of P. destructor DNA (∼100 plasmid copies/μl), with amplification efficiency = 0.95. The assay was validated against a panel of target and nontarget oomycetes, which showed that the primers were specific for Plasmopara spp., while the probe was specific for P. destructor infecting both I. walleriana and I. balsamina. Testing of Impatiens tissue collected from 23 locations across 13 states indicated all samples with IDM symptoms tested positive for P. destructor. Asymptomatic plants from two locations also tested positive for P. destructor.

Garlic Volatile Diallyl Disulfide Induced Cucumber Resistance to Downy Mildew

Allicin compositions in garlic are used widely as fungicides in modern agriculture, in which diallyl disulfide (DADS) is a major compound. Downy mildew, caused by Pseudoperonospora cubensis (P. cubensis), is one of the most destructive diseases and causes severe yield losses in cucumbers. To explore the potential mechanism of DADS-induced cucumber resistance to downy mildew, cucumber seedlings were treated with DADS and then inoculated with P. cubensis at a 10-day interval. Symptom observation showed that DADS significantly induced cucumber resistance to downy mildew. Furthermore, both lignin and H₂O₂ were significantly increased by DADS treatment to responding P. cubensis infection. Simultaneously, the enzyme activities of peroxidase (POD) in DADS-treated seedlings were significantly promoted. Meanwhile, both the auxin (IAA) and salicylic acid (SA) contents were increased, and their related differentially expressed genes (DEGs) were up-regulated when treated with DADS. Transcriptome profiling showed that many DEGs were involved in the biological processes of defense responses, in which DEGs on the pathways of 'phenylpropanoid biosynthesis', 'phenylalanine metabolism', 'MAPK signaling', and 'plant hormone signal transduction' were significantly up-regulated in DADS-treated cucumbers uninoculated with the pathogen. Based on the results of several physiological indices and transcriptomes, a potential molecular mechanism of DADS-induced cucumber resistance to downy mildew was proposed and discussed. The results of this study might give new insight into the exploration of the induced resistance mechanism of cucumber to downy mildew and provide useful information for the subsequent mining of resistance genes in cucumber.

CRISPR-Editing of Sweet Basil (Ocimum basilicum L.) Homoserine Kinase Gene for Improved Downy Mildew Disease Resistance

Sweet basil (Ocimum basilicum L.) downy mildew disease (DM) caused by Peronospora belbahrii is a worldwide threat to the basil industry due to the lack of natural genetic resistance in sweet basil germplasm collections. In this study, we used CRISPR-gene editing to modify the sweet basil DM susceptibility gene homoserine kinase (ObHSK). Gene-edited plants challenged with P. belbahrii displayed a significantly reduced susceptibility to DM, based on phenotypic disease indices and on in planta pathogen load. These results suggest that ObHSK plays a role in conditioning DM susceptibility, similar to that observed for the AtHSK gene in Arabidopsis. These results demonstrate the utility of CRISPR-gene editing in enhancing DM resistance and contributing to sweet basil breeding programs.