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BACKGROUND: Stilbenoid extracts, such as those originating from grapevine by‐products (e.g. canes), are of interest for use as biopesticides in vineyard owing to their antimicrobial activities. However, stilbenoids are unstable in the environment, especially under light. This study aimed to chemically characterize the effect of UV light on stilbenoids present in a grapevine cane extract (CE), and to evaluate the antimicrobial activities against two major grapevine pathogens (Plasmopara viticola and Botrytis cinerea) of grapevine extracts exposed to UV. RESULTS: Treatment with UV (365 nm) on a grapevine CE led to degradation of stilbenoids (up to 71% after 1 h). The stilbenoid stability depended on their chemical structure: only those possessing CC, as trans‐resveratrol and trans‐ε‐viniferin, were affected with first their isomerization and secondly their oxidation/cyclization. As a consequence, UV‐exposed extracts (UV‐CEs) showed reduced antimicrobial activities against the two pathogens (mycelium and spores). For instance, regarding P. viticola, an UV‐CE exposed during 4 h showed an almost total loss of its activity on oomycete development and a 2.4‐fold inhibition of zoospore mobility in comparison to CE. For B. cinerea, the inhibition capacity of the same UV‐CE was reduced by only 1.1‐fold on mycelial development and by 3.2‐fold on conidial germination compared to CE. CONCLUSION: UV light triggered modifications on the structure of bioactive stilbenoids, resulting in losses of their antimicrobial activities. Photoprotection of stilbenoids has to be considered in the perspective of using them in vineyards as biopesticides. © 2024 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

Globally sustainable disease management ensuring high quality in grapes is in demand as it holds significant importance as a versatile fruit for consumption, winemaking, and production of various products such as grape juice, raisin, and grape‐seed oil. The present paper reports a combination of nano‐biotechnology as a promising strategy for enhancing plant health and fruit productivity in grapes combining Irradiated chitosan nanoparticles and bio‐control agents. The Irradiated Chitosan with Bacillus subtilis and Trichoderma viridae and pesticides were evaluated for disease management. Percent disease index, percent disease control, and percent yield enhancement in Cymoxanil 8% + Mamcozeb 64% WP @ 0.2% treatment were as 17. 24%, 67.97% and 33.91% in 150 ppm Irradiated chitosan+B. subtilis were 19.83, 63.16, 30.41 and in Trichoderma 150 ppm Irradiated chitosan were 24.58, 54.33, and 27.40, respectively as compared to untreated crop with disease severity 53.84% PDI. Thus, irradiated chitosan and Bacillus subtilis elucidated a synergistic combination for residue‐free efficient phytosanitary measures, which harnessed the strength of chitosan and bio‐control agents for sustainable grape productivity. These findings will also pave the way for a deeper understanding of the synergistic interaction between Irradiated nanochitosan and bio‐control agents for an eco‐friendly and economically viable disease management strategy. The minimum temperature and morning relative humidity (RH I) had positive significance, with correlation coefficients of 0.484 and 0.485, respectively. The evening relative humidity (RH II) had a positive highly significant positive correlation coefficient of 0.664. Chitosan merits as a multiple stress tolerance enhancing agent that will further help in mitigating climate change adaptations in grapevines reducing reliance on chemical agro‐inputs. [ABSTRACT FROM AUTHOR]

Downy mildew caused by Sclerospora graminicola is a systemic disease that affects the yield and quality of foxtail millet. This obligate biotrophic oomycete manipulates host physiology and immune processes through numerous effectors. A thorough comprehension of effector biology is crucial to unravel disease mechanisms and understand host plant resistance. In this study, bioinformatic analyses revealed 498 potentially secreted proteins in S. graminicola, of which 62 were identified as RXLR effectors; 46 RXLR‐encoding genes exhibited upregulated expression during the early stages of infection. To elucidate the functions of these secreted proteins, a heterogeneous expression system was developed using Nicotiana benthamiana. Twenty‐one RXLR effectors secreted by S. graminicola were transiently expressed in N. benthamiana, of which four could suppress INF1‐triggered cell death. Various defence responses in N. benthamiana were attenuated, including inhibition of defence gene expression, reduction of reactive oxygen species (ROS) accumulation and diminished callose deposition. The expression of SG_RXLR41 also enhanced the growth of Phytophthora capsici on N. benthamiana leaves. These findings indicate that S. graminicola facilitates infection and expansion through the secretion of multiple RXLR effectors, and SG_RXLR41 is an important virulence‐related effector that is involved in manipulating plant immunity by suppressing cell death. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Summary: The plant cell wall is the first line of defence against physical damage and pathogen attack. Wall‐associated kinase (WAK) has the ability to perceive the changes in the cell wall matrix and transform signals into the cytoplasm, being involved in plant development and the defence response. Downy mildew, caused by Hyaloperonospora brassicae, can result in a massive loss in Chinese cabbage (Brassica rapa L. ssp. pekinensis) production. Herein, we identified a candidate resistant WAK gene, BrWAK1, in a major resistant quantitative trait locus, using a double haploid population derived from resistant inbred line T12–19 and the susceptible line 91–112. The expression of BrWAK1 could be induced by salicylic acid and pathogen inoculation. Expression of BrWAK1 in 91–112 could significantly enhance resistance to the pathogen, while truncating BrWAK1 in T12–19 increased disease susceptibility. Variation in the extracellular galacturonan binding (GUB) domain of BrWAK1 was found to mainly confer resistance to downy mildew in T12–19. Moreover, BrWAK1 was proved to interact with BrBAK1 (brassinosteroid insensitive 1 associated kinase), resulting in the activation of the downstream mitogen‐activated protein kinase (MAPK) cascade to trigger the defence response. BrWAK1 is the first identified and thoroughly characterized WAK gene conferring disease resistance in Chinese cabbage, and the plant biomass is not significantly influenced by BrWAK1, which will greatly accelerate Chinese cabbage breeding for downy mildew resistance. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Onion downy mildew caused by Peronospora destructor has been widespread in Japan since 2016. Soil disinfection and use of fungicides have been implemented as control measures against oospores in the soil, which are the primary source of infection. Measurements of oospore density are needed to clarify the risk of disease development and inform disease management. In this study, an experimental system capable of detecting P. destructor DNA from field samples was developed. A TaqMan probe‐type primer was used to target the coxII (cytochrome c oxidase subunit II) region of the mitochondrial genome of P. destructor and no false positives were observed. Using this method, the detection limit was equivalent to 5 oospores of P. destructor/g soil in grey lowland soil and andosol. The correlation coefficient between oospore density and the primary infection rate was investigated by testing soil samples from 115 fields. Although no correlations between oospore density and the primary infection were observed in pesticide‐treated fields, significant correlations were observed in untreated fields. Continuous cropping of onions increased the oospore density. The correlation between primary and secondary infection was relatively weak, and the negative predictive value of primary infection was relatively high (89.0). These results suggest that the disease‐risk potential of onion downy mildew is very high, and thus it is necessary to set a low pathogen detection threshold. The system presented here provides a highly sensitive method for supporting decision‐making aimed at disease control. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Rapeseed (Brassica napus) production in Australia relies heavily on triazine‐or glyphosate‐tolerant cultivars. For 14 triazine‐tolerant cultivars, disease development of Neopseudocercosporella capsellae (white leaf spot), Alternaria brassicae and A. japonica (Alternaria leaf spot), and Hyaloperonospora brassicae (downy mildew) were all dependent upon herbicide application timing (p < 0.001), with significant differences between cultivars (p < 0.001) and a significant interaction (p < 0.001) between herbicide application timing and cultivars. Atrazine applied preinfection by N. capsellae, A. brassicae, or A. japonica enhanced disease incidence, severity, and leaf collapse, while atrazine application postinfection for these same pathogens reduced all three disease parameters. However, for H. brassicae, application of atrazine after, and especially prior to, infection resulted in lower disease incidence, severity, and leaf collapse. Application of glyphosate on five glyphosate‐tolerant cultivars for N. capsellae resulted in significant differences (p < 0.05) between glyphosate application treatments, and between host cultivars in terms of incidence and consequent leaf collapse. For A. brassicae, A. japonica, and H. brassicae, glyphosate resulted in significant differences (p < 0.001) across application timings between cultivars, and a significant interaction (p < 0.001) between herbicide application timings and cultivars. Glyphosate applied on glyphosate‐resistant rapeseed after, and especially prior to, attack by H. brassicae, reduced downy mildew. These are the first studies to highlight how the timing of application of triazine or glyphosate in relation to pathogen infection is critical to the susceptibility of rapeseed to white leaf spot, Alternaria leaf spot, and downy mildew. This new understanding offers fresh possibilities for improved management of these diseases in herbicide‐tolerant rapeseed crops. [ABSTRACT FROM AUTHOR]

During the winter, there is a high occurrence of downy mildew on lettuce caused by Bremia lactucae. This oomycete shows variability in virulence, so understanding the genetic structure of the pathogen population becomes essential for obtaining resistant cultivars. Thus, the objective of this study was to determine sexual compatibility in Brazilian populations of B. lactucae and investigate the occurrence of sexual reproduction of the pathogen on lettuce (Lactuca sativa) and prickly lettuce (Lactuca serriola). Leaf samples were collected in 33 municipalities in seven Brazilian states. The virulence structure of the populations was monitored using the EU‐C sextet code. B. lactucae populations from the states of São Paulo, Paraná, Rio de Janeiro, and Rio Grande do Sul shared six of the 15 virulence factors evaluated. Twenty‐five virulence phenotypes (v‐phenotypes) were found, with the sextet codes 31‐00‐02, 31‐16‐02, 31‐24‐02, and 31‐01‐02 being more frequent. The predominance of some v‐ phenotypes indicates that clonal reproduction is still the main form of B. lactucae propagation. The genes and resistance factors of the cultivars Argelès (Dm38), Balesta, and Bartoli are recommended as suitable sources of lettuce resistance in Brazil. Natural occurrence of oospores was detected in most sampled locations, in lettuce and prickly lettuce plants. Virulence variability of Brazilian isolates is the result of the pathogen's ability to reproduce both sexually and asexually, with a prevalence of homothallic isolates; although the majority were of the predominant B2 mating type, there was a high incidence of predominant B1 in addition to B1 = B2. [ABSTRACT FROM AUTHOR]

It is unknown whether the downy mildew severity observed at this site would influence I C. concatenata i foliar longevity or suitability for I Pieris i spp. oviposition. Keywords: downy mildew; spring ephemeral EN downy mildew spring ephemeral 1 3 3 12/29/22 20221001 NES 221001 In May 2022, a heavily diseased patch of the spring ephemeral, I Cardamine concatenata i , was observed in Gambrill State Park (39.46425° N, 77.49221° W) in Frederick County, Maryland, USA. High incidence of Hyaloperonospora cardamines-laciniatae on Cardamine concatenata in Maryland, USA. [Extracted from the article]

BACKGROUND: Cucumber plants suffer from a serious threatening disease, downy mildew, throughout the growing seasons irrespective of the weather temperature. The causal agent, Pseudoperonospora cubensis, tends to evolve rapidly upon sequential applications of chemical fungicides and generate new progeny possessing tolerance to such fungicides. Glycoproteins represent an environmentally safe alternative for chemically synthetized fungicides and do not trigger fungicide resistance. We studied the antifungal activity of four glycoproteins namely soybean β‐conglycinin, chickpea vicilin, duck egg ovomucin and catfish p22 against P. cubensis. Ten commercial fungicides of different chemical groups were used as positive controls of glycoprotein treatments. RESULTS: The results revealed that soybean β‐conglycinin and catfish p22 glycoproteins possess significant antifungal activity against P. cubensis. The amount of disease suppression caused by β‐conglycinin and p22 was comparable to the highly efficient chemical fungicides containing copper oxychloride, cymoxanil and fosetyl Al as active ingredients. Vicilin and ovomucin were less efficient biocides as they gave moderate suppression of disease severity. However, all tested glycoproteins provided full protection for the newly emerged cucumber leaves. Microscopic examination of glycoprotein‐treated leaves inferred the ability of catfish p22 and soybean β‐conglycinin to disrupt the integrity of sporangial cell walls of P. cubensis rendering them non‐viable compared to untreated ones. Expression levels of total phenolic compounds and the antioxidant enzymes catalase, superoxide dismutase and peroxidase were elevated upon glycoproteins application, which infers their involvement in disease suppression. CONCLUSION: This report emphasizes the direct and indirect roles of glycoproteins in safe management of cucumber downy mildew disease. © 2021 Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

Geographical distribution and diversity of current plant species have been strongly shaped by climatic oscillations during the Quaternary. Analysing the resulting divergence among species and differentiation within species is crucial to understand the evolution of taxa like the Vitis genus, which provides very useful genetic resources for grapevine improvement and might reveal original recolonization patterns due to growth habit and dispersal mode. Here, we studied the genetic structure in natural populations of three species from eastern North America: Vitis aestivalis, V. cinerea and V. riparia using different marker types. Vitis aestivalis and V. cinerea showed higher diversity than V. riparia. The two former species are less differentiated, confirming an earlier divergence of V. riparia. V. aestivalis and V. riparia exhibited different genetic groups on both sides of the Appalachian Mountains that could mirror different recolonization routes from southern refugia. Genetic structure was stronger in V. cinerea, for which two varieties (var. berlandieri and var. cinerea) are morphologically recognized. Our results confirm this distinction and suggest the existence of three other lineages within var. cinerea. These discontinuities appear linked to adaptation of var. berlandieri to dry and limy areas of Texas and partially to the Mississippi River Valley. Rapid range expansions from refugia upon climate warming are also suggested by the low linkage disequilibrium values observed. Furthermore, large variation for downy mildew resistance was observed in the three species. Our findings appeared consistent with the vegetation history of eastern North America. [ABSTRACT FROM AUTHOR]

The North Georgia Mountains are the southernmost region along the United States East Coast where European wine grapes (Vitis vinifera) are grown commercially. Epidemics of downy mildew, caused by Plasmopara viticola, are frequent and severe, but little is known about the epidemiology and population biology of the pathogen in this region. Disease monitoring in an experimental vineyard from 2015 to 2017 indicated that times of disease onset and progress rates were highly variable across years and cultivars. Oospores were observed microscopically, and simulation with a process‐based model indicated presence of conditions favourable for oospore germination in the spring and early summer each year. A total of 409 P. viticola isolates collected over three years were genotyped with seven microsatellite markers, revealing very high genotypic diversity, which when combined with the observation of oospores is indicative of a sexually reproducing population. Among the 409 isolates, 225 multilocus genotypes (MLGs) were identified, of which 164 were detected only once and 61 were repeated (clonal). Eight MLGs (represented by 28 isolates) were detected across years, suggesting the possibility of asexual overwintering of P. viticola in this region. Across sampling dates, the percentage of isolates belonging to nonrepeated (unique) MLGs ranged from 27.3% to 63.2%. Even towards the end of the annual epidemic, the percentage of isolates in nonrepeated MLGs was still relatively high, around 30%. These MLGs may have originated from oospores germinating late during the growing season, although incomplete sampling at earlier dates and contribution by immigration cannot be fully excluded. [ABSTRACT FROM AUTHOR]

Disease development in plants requires a susceptible host, a virulent pathogen, and a favourable environment. Oomycete pathogens cause many important diseases and have evolved sophisticated molecular mechanisms to manipulate their hosts. Day length has been shown to impact plant–oomycete interactions but a need exists for a tractable reference system to understand the mechanistic interplay between light regulation, oomycete pathogen virulence, and plant host immunity. Here we present data demonstrating that light is a critical factor in the interaction between Arabidopsis thaliana and its naturally occurring downy mildew pathogen Hyaloperonospora arabidopsidis (Hpa). We investigated the role of light on spore germination, mycelium development, sporulation, and oospore formation of Hpa, along with defence responses in the host. We observed abundant Hpa sporulation on compatible Arabidopsis under day lengths ranging from 10 to 14 hr. In contrast, exposure to constant light or constant dark suppressed sporulation. Exposure to constant dark suppressed spore germination, mycelial development, and oospore formation, whereas exposure to constant light stimulated these three stages of development. A biomarker of plant immune system activation was induced under both constant light and constant dark. Altogether, these findings demonstrate that Hpa has the molecular mechanisms to perceive and respond to light and that both the host and pathogen responses are influenced by the light regime. Therefore, this pathosystem can be used for investigations to understand the molecular mechanisms through which oomycete pathogens like Hpa perceive and integrate light signals, and how light influences pathogen virulence and host immunity during their interactions. [ABSTRACT FROM AUTHOR]

A spectrophotometric method for determining the viability of sporangia and zoospores of the oomycete Plasmopara viticola (causal agent of grapevine downy mildew) is described and evaluated to overcome the limitations of currently available methods for assessing propagule viability. Sporangia produced on leaf discs in the laboratory were harvested at different days after the initiation of sporulation (DAS) to yield differences in sporangium viability. Sporangia were suspended in sterile water, the suspensions were placed in a cuvette, and sporangium germination was monitored in a spectrophotometer (λ = 600 nm) at 2‐ to 3‐min intervals for 5 hr. Absorbance started to increase after sporangia were suspended in water for ~30–60 min followed by major peak(s) for younger sporangia (1–3 DAS), whereas low to no increase in absorbance was observed for senescent sporangia (>7 DAS). Microscopic observation confirmed that the increase in absorbance corresponded to the release and active swimming of zoospores, whereas absorbance decreased when zoospores encysted and settled. A positive correlation (r =.839, p =.0365) was observed when the time to the initial increase in absorbance was plotted against the age of sporangia. The time to the absorbance peak (marking the time of maximum zoospore movement) was shortest for immature sporangia (0 DAS), longest for young sporangia (2 DAS) and decreased for mature and senescent sporangia. A similar pattern was observed for the standardized area under the absorbance curve (indicating the overall quantity of zoospores released), for which values were lowest for immature and senescent sporangia, highest for young sporangia and intermediate for mature sporangia. Consistent patterns obtained across two independent experiments suggest that the method is reproducible and may be further developed for other zoospore‐releasing pathogens. [ABSTRACT FROM AUTHOR]

Grapes downy mildew caused by obligate oomycete plant pathogen Plasmopara viticola is a devastating disease worldwide, resulting in significant yield and quality losses. A field survey was conducted in two major grapes cultivated areas of Tamil Nadu for the incidence of grapevine downy mildew. The disease incidence was 43.42%–76.69%, and the highest disease incidence of 76.69% was observed in the Theni district. Totally eight P. viticola isolates were collected from different places in Coimbatore and Theni districts. These isolates were confirmed through microscopic observation and sequencing of COX 2 gene, and the phylogenetic tree was developed to study their phylogenetic relationship among the isolates which shows 97–100% sequence similarity with other P. viticola isolates and less sequence similarity with Plasmopara species. The loop‐mediated isothermal amplification (LAMP) assay was developed based on the CesA4 gene sequence of P. viticola. The assay developed was more sensitive as it detected P. viticola genomic DNA up to 20 fmg. LAMP assay specificity was proved by carrying out the assay with genomic DNA extracted from other Oomycetes and fungal plant pathogens. Finally, LAMP assay was validated by testing seventy‐eight grapevine leaf samples collected from seven different locations. LAMP assay showed a positive reaction in sixty‐two samples tested out of seventy‐eight samples tested. Therefore, the LAMP assay described should helpful for early and specific detection of downy mildew pathogen and help in mitigating disease incidence. [ABSTRACT FROM AUTHOR]

Summary: Gene silencing exists in eukaryotic organisms as a conserved regulation of the gene expression mechanism. In general, small RNAs (sRNAs) are produced within the eukaryotic cells and incorporated into an RNA‐induced silencing complex (RISC) within cells. However, exogenous sRNAs, once delivered into cells, can also silence target genes via the same RISC. Here, we explored this concept by targeting the Cellulose synthase A3 (CesA3) gene of Hyaloperonospora arabidopsidis (Hpa), the downy mildew pathogen of Arabidopsis thaliana. Hpa spore suspensions were mixed with sense or antisense sRNAs and inoculated onto susceptible Arabidopsis seedlings. While sense sRNAs had no obvious effect on Hpa pathogenicity, antisense sRNAs inhibited spore germination and hence infection. Such inhibition of infection was not race‐specific, but dependent on the length and capping of sRNAs. Inhibition of infection by double stranded sRNA was more efficient than that observed with antisense sRNA. Thus, exogenous sRNA targeting conserved CesA3 could suppress Hpa infection in Arabidopsis, indicating the potential of this simple and efficient sRNA‐based approach for deciphering gene functions in obligate biotrophic pathogens as well as for R‐gene independent control of diseases in plants. [ABSTRACT FROM AUTHOR]

Previous phylogenetic studies of the grape downy mildew pathogen, Plasmopara viticola, revealed five cryptic species in eastern North America that differed in their host range and geographic distribution. Preliminary comparative studies also documented differences in temperature responses during infection between certain cryptic species, indicating the biological relevance of knowing which cryptic species of the pathogen are present in a given region. However, limited information is available regarding the presence, prevalence and dynamics of cryptic species of P. viticola in the southeastern United States. Here, 301 P. viticola isolates obtained from cultivated grape species in five distinct grape‐growing regions of Georgia and Florida were subjected to cleaved amplified polymorphic sequence analysis and multilocus sequencing (internal transcribed spacer region of the rDNA, actin and β‐tubulin) to identify cryptic species and infer phylogenetic relationships. Three cryptic species, P. viticola clade aestivalis (Pva), clade vinifera (Pvv) and clade vulpina (Pvu), were identified in Georgia, whereas two, Pva and Pvv, were found in Florida; all three cryptic species are reported here for the first time in Georgia, whereas Pva is reported for the first time in Florida. Pva was the most prevalent cryptic species (72.1% of isolates) and was distributed widely from the North Georgia Mountains to Mid‐Florida, whereas Pvv (27.2%) and Pvu (0.7%) were found only in the Coastal Plain region of the two states. Interestingly, Pvu was obtained from French American hybrid Blanc du Bois and could be subcultured on Vitis vinifera Chardonnay, suggesting a broader host range than only the wild species Vitis vulpina reported previously. [ABSTRACT FROM AUTHOR]

Summary: Bacillus subtilis GLB191 (hereafter GLB191) is an efficient biological control agent against the biotrophic oomycete Plasmopara viticola, the causal agent of grapevine downy mildew. In this study, we show that GLB191 supernatant is also highly active against downy mildew and that the activity results from both direct effect against the pathogen and stimulation of the plant defences (induction of defence gene expression and callose production). High‐performance thin‐layer chromatography analysis revealed the presence of the cyclic lipopeptides fengycin and surfactin in the supernatant. Mutants affected in the production of fengycin and/or surfactin were thus obtained and allowed us to show that both surfactin and fengycin contribute to the double activity of GLB191 supernatant against downy mildew. Altogether, this study suggests that GLB191 supernatant could be used as a new biocontrol product against grapevine downy mildew. [ABSTRACT FROM AUTHOR]

BACKGROUND: Complex III inhibitors are key compounds in the control of Plasmopara viticola. They are prone to the development of resistance, as demonstrated by the emergence of resistance to quinone‐outside inhibitors. By using a combination of bioassays and molecular methods, we monitored sensitivity to amisulbrom and ametoctradin in P. viticola populations in French vineyards from 2012 to 2017. RESULTS: We found that the alternative oxidase (AOX)‐related resistance mechanism was common in French P. viticola populations. Target‐site resistance to ametoctradin was first detected in 2015 and is likely caused by a single point mutation in the cytochrome b gene, leading to the S34L substitution. The role of this substitution in resistance to ametoctradin was corroborated by another study using an experimental model. A molecular biology method has been developed to detect the mutant allele. To date, the frequency of this mutation is low in French P. viticola populations and it is often co‐detected with the wild‐type allele. CONCLUSION: Populations of P. viticola displaying evidence of AOX‐related resistance were detected for every surveyed year, and their occurrence in French vineyards seems to be increasing over time. This resistance mechanism is currently threatening the efficacy of complex III inhibitors in the field. The low frequency of the S34L allele conferring resistance to ametoctradin, and the instability of resistant phenotypes in some populations, suggest that a fitness cost may be associated with the mutation. © 2019 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

BACKGROUND: Cerevisane, made up of cell wall derivatives from the Saccharomyces cerevisiae strain LAS117, is proposed as a resistance inducer in plants. The mode of action of cerevisane was investigated through transcriptome analysis (RNA‐Seq) carried out on leaves of potted vines cv. Italia grown in the greenhouse and sprayed at 1‐week intervals with cerevisane. Analyses were performed at three time points after one and three sprays as well as on vines challenged with artificial inoculation with Plasmopara viticola, Erysiphe necator and Botrytis cinerea. RESULTS: Cerevisane proved effective against downy mildew and caused an increase in expression levels of several genes related to defense responses to fungal pathogens and other stresses and down‐regulation of genes involved in several processes related to plant growth and development. Up‐regulated genes included genes encoding (i) enzymes involved in hormone metabolism (i.e. salicylic acid, jasmonate, ethylene) and related plant responses, (ii) defense compounds (i.e. pathogenesis‐related proteins, phenylalanine ammonia‐lyase, stilbene synthases, lipoxygenase, leucine‐rich repeat receptor‐like protein kinases, non‐specific plant lipid transfer proteins, serine–threonine protein kinases involved in signal transduction, superoxide dismutase and glutathione S‐transferase involved in response to oxidative stress), (iii) secondary metabolites (i.e. phenylpropanoids, terpenoids, lignin), and (iv) photosynthetic processes (light harvesting chlorophyll A/B‐binding proteins and components of the photosystems). CONCLUSION: Cerevisane can be a useful tool in protection schedules against downy mildew on grapevine aimed at reducing the usage of synthetic fungicides and preventing fungicide resistance. The results provide the first basic knowledge on the mode of action of yeast‐derived elicitors effective against P. viticola on grapevine. © 2019 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Summary: The grapevine downy mildew pathogen Plasmopara viticola secretes a set of RXLR effectors (PvRXLRs) to overcome host immunity and facilitate infection, but how these effectors function is unclear. Here, the biological function of PvRXLR131 was investigated via heterologous expression. Constitutive expression of PvRXLR131 in Colletotrichum gloeosporioides significantly enhanced its pathogenicity on grapevine leaves. Constitutive expression of PvRXLR131 in Arabidopsis promoted Pseudomonassyringae DC3000 and P.syringae DC3000 (hrcC‐) growth as well as suppressed defence‐related callose deposition. Transient expression of PvRXLR131 in Nicotiana benthamiana leaves could also suppress different elicitor‐triggered cell death and inhibit plant resistance to Phytophthora capsici. Further analysis revealed that PvRXLR131 interacted with host Vitis vinifera BRI1 kinase inhibitor 1 (VvBKI1), and its homologues in N. benthamiana (NbBKI1) and Arabidopsis (AtBKI1). Moreover, bimolecular fluorescence complementation analysis revealed that PvRXLR131 interacted with VvBKI1 in the plasma membrane. Deletion assays showed that the C‐terminus of PvRXLR131 was responsible for the interaction and mutation assays showed that phosphorylation of a conserved tyrosine residue in BKI1s disrupted the interaction. BKI1 was a receptor inhibitor of growth‐ and defence‐related brassinosteroid (BR) and ERECTA (ER) signalling. When silencing of NbBKI1 in N. benthamiana, the virulence function of PvRXLR131 was eliminated, demonstrating that the effector activity is mediated by BKI1. Moreover, PvRXLR131‐transgenic plants displayed BKI1‐overexpression dwarf phenotypes and suppressed BR and ER signalling. These physiological and genetic data clearly demonstrate that BKI1 is a virulence target of PvRXLR131. We propose that P. viticola secretes PvRXLR131 to target BKI1 as a strategy for promoting infection. [ABSTRACT FROM AUTHOR]

Downy mildew (Plasmopara viticola) is one of the most important diseases in grape‐growing areas worldwide, including Brazil. To examine pathogen population biology and structure, P. viticola was sampled during the 2015/16 growing season from 516 lesions on nine grape cultivars in 11 locations in subtropical areas of São Paulo State, Brazil. For identification of cryptic species, a subsample of 130 isolates was subjected to cleaved amplified polymorphic sequence (CAPS) analysis, and for 91 of these isolates the ITS1 region was sequenced. These analyses suggest that the population of P. viticola in São Paulo State consists of a single cryptic species, P. viticola clade aestivalis. Seven microsatellite markers were used to determine the genetic structure of all 516 P. viticola isolates, identifying 23 alleles and 55 multilocus genotypes (MLGs). Among these MLGs, 34.5% were clonal and represented 93% of the isolates sampled. Four dominant genotypes were present in at least five different locations, corresponding to 65.7% of the isolates sampled. Genotypic diversity (Ĝ = 0.21–0.89) and clonal fraction (0.58–0.96) varied among locations (populations). Most populations showed significant deviation from Hardy–Weinberg expectations; in addition, excess of heterozygosity was verified for many loci. However, principal coordinate analysis revealed no clusters among locations and no significant isolation by distance was found, suggesting high levels of migration. The results indicate that downy mildew epidemics result from multiple clonal infections caused by a few genotypes of P. viticola, and reproduction of P. viticola in São Paulo State is predominantly asexual. [ABSTRACT FROM AUTHOR]

BACKGROUND: The development of fungicide resistance by pathogens is a major limiting factor for the control of plant diseases. To combat resistance development, the use of broad‐spectrum but nonfungitoxic resistance inducers such as acibenzolar‐S‐methyl (ASM) is a promising approach because the orchestrated mechanisms underlying systemic acquired resistance induced by ASM are less likely to be overcome easily by pathogens. However, phytotoxicity is the main limiting factor of ASM. RESULTS: ASM was highly active at inducing systemic resistance against powdery and downy mildews, the two major cucumber diseases. Based on the duration of the control, ASM effectiveness against these diseases was maintained well in plastic greenhouses and the number of sprays could be reduced. Control efficacy after seed treatment with ASM and the applications of microencapsulated ASM was also high against mildews in pots as well as in greenhouse experiments, with no problematic phytotoxicity. CONCLUSION: The use of ASM is a potential integrated pest management‐based tactic to control cucumber powdery and downy mildews because its long‐lasting efficacy allows the application of typical fungicides to be reduced. The risk for resistance development in mildew pathogens will also be reduced. ASM seed treatment as well as soil amendment with microencapsulated ASM is effective in lowering the risk for the phytotoxicity of this compound. © 2018 Society of Chemical Industry The use of resistance inducer acibenzolar‐S‐methyl (ASM) and its microencapsulated formulations is a potential integrated pest management‐based tactic to control cucumber diseases because their long‐lasting efficacy allows the application of typical fungicides to be reduced. The risk for resistance development in pathogens will also be reduced when ASM is included as a tool to control cucumber diseases. [ABSTRACT FROM AUTHOR]

Summary: Plant‐pathogenic oomycetes secrete effector proteins to suppress host immune responses. Resistance proteins may recognize effectors and activate immunity, which is often associated with a hypersensitive response (HR). Transient expression of effectors in plant germplasm and screening for HR has proven to be a powerful tool in the identification of new resistance genes. In this study, 14 effectors from the lettuce downy mildew Bremia lactucae race Bl:24 were screened for HR induction in over 150 lettuce accessions. Three effectors—BLN06, BLR38 and BLR40—were recognized in specific lettuce lines. The recognition of effector BLR38 in Lactuca serriola LS102 did not co‐segregate with resistance against race Bl:24, but was linked to resistance against multiple other B. lactucae races. Two unlinked loci are both required for effector recognition and are located near known major resistance clusters. Gene dosage affects the intensity of the BLR38‐triggered HR, but is of minor importance for disease resistance. [ABSTRACT FROM AUTHOR]

BACKGROUND: Despite anti‐resistance strategies being recommended to reduce selection pressure on insensitive strains, no information is available on fungal population dynamics following their application in real field conditions. In this study, the effects on Plasmopara viticola populations of two identical spray programs, differing only in including or not the carboxylic acid amide (CAA) mandipropamid in mixture and in alternation with an anti‐resistance partner, were compared in terms of downy mildew control efficacy and mandipropamid sensitivity in two commercial vineyards for four seasons. RESULTS: Both programs effectively and similarly protected grapevine from downy mildew, despite different starting sensitivity levels of the P. viticola populations. In the vineyard where resistant strains were initially present, the frequency of mutations associated with resistance (G1105S/V) fluctuated within seasons in both programs and a shift towards sensitivity occurred after 3 years of the mandipropamid‐free program. Where sensitivity was initially present, no changes occurred in the mandipropamid‐free program and resistant strains were selected in the mandipropamid program in high disease pressure conditions. CONCLUSION: The anti‐resistance strategy including mandipropamid in mixture showed a good field performance, but did not completely prevent an increase in the frequency of insensitive strains. This supports the need for appropriate planning to determine which mixtures should be used in the field. © 2018 Society of Chemical Industry Fungicide resistance management is crucial in plant disease protection. The effectiveness of anti‐resistance strategies under real field conditions is evaluated considering the complex interaction among fungicide, pathogen, host and environment. [ABSTRACT FROM AUTHOR]

Pseudoperonospora cubensis, the causal agent of cucurbit downy mildew ( CDM), is known to exhibit host specialization. The virulence of different isolates of the pathogen can be classified into pathotypes based on their compatibility with a differential set composed of specific cucurbit host types. However, the genetic basis of host specialization within P. cubensis is not yet known. Total genomic DNA extracted from nine isolates of P. cubensis collected from 2008 to 2013 from diverse cucurbit host types ( Cucumis sativus, C. melo var. reticulatus, Cucurbita maxima, C. moschata, C. pepo, and Citrullus lanatus) in the United States were subjected to whole-genome sequencing. Comparative analysis of these nine genomes confirmed the presence of two distinct evolutionary lineages (lineages I and II) of P. cubensis. Many fixed polymorphisms separated lineage I comprising isolates from Cucurbita pepo, C. moschata, and Citrullus lanatus from lineage II comprising isolates from Cucumis spp. and Cucurbita maxima. Phenotypic characterization showed that lineage II isolates were of the A1 mating type and belonged to pathotypes 1 and 3 that were not known to be present in the United States prior to the resurgence of CDM in 2004. The association of lineage II isolates with the new pathotypes and a lack of genetic diversity among these isolates suggest that lineage II of P. cubensis is associated with the resurgence of CDM on cucumber in the United States. [ABSTRACT FROM AUTHOR]

Basil is an economically important herb in the United States and in the world. Recent epidemics of basil downy mildew, caused by Peronospora belbahrii, have significantly affected basil production in the United States. ProPhyt (potassium phosphite), Actigard (acibenzolar-S-methyl) and Organocide (sesame oil) were evaluated in the greenhouse in the presence or absence of red light for their effects on the severity of downy mildew and sporangial production by P. belbahrii. Red light at intensity of 12 μmol photons/m2/s significantly ( P < 0.05) reduced severity of downy mildew in basil. ProPhyt-treated basil plants had the lowest disease severity irrespective of red light exposure. Basil plants treated with Actigard and Organocide under red light had significantly lower disease severity compared to plants under dark conditions with the same fungicide treatments 14 and 13 days after inoculation ( DAI) in experiments 1 and 2, respectively. Red light significantly reduced AUDPC in the treatments of Actigard and Organocide in both experiments. Basil plants treated with Actigard and Organocide under red light had significantly reduced number of P. belbahrii sporangia than those under dark conditions receiving the same fungicide treatments. This is the first report demonstrating red light in combination with Actigard and Organocide for improved management of downy mildew in greenhouse-grown basil. [ABSTRACT FROM AUTHOR]

BACKGROUND There is growing demand to replace chemical pesticides with alternatives owing to concerns related to impacts on human health and the environment. Plant-derived plant protection products could provide sustainable and environmentally friendly alternatives to chemical products. The aim of this study was to identify plant and fungal extracts with so far unknown activity against important plant pathogens by in vitro screening of a library of more than 3000 extracts. RESULTS Several plant extracts with promising in vitro fungicidal activity ( MIC100 ≤ 50 µg mL−1) towards one or several of the investigated pathogens ( Venturia ineaqualis, Phytophthora infestans, Plasmopara viticola) were identified by the screening. One of the hits, an ethyl acetate extract of Juncus effusus L. medulla, was further investigated, and dehydroeffusol ( DHEF) was identified as its main active constituent. On susceptible grapevine and apple seedlings, efficacies of up to 100% were reached with the extract ( EC50 123 or 156 µg mL−1) and with DHEF ( EC50 18 or 21 µg mL−1) against P. viticola and V. inaequalis respectively. CONCLUSIONS Our results demonstrate that plants can provide promising alternatives for integrated and organic farming. J. effusus shows high efficacy at low concentrations and, as an abundant perennial species, is an interesting candidate for the development of a novel plant protection product. © 2015 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Plasmopara halstedii and Plasmopara viticola are the causative agents of downy mildew of two economically important crops, sunflower and grapevine, respectively. These phylogenetically related oomycetes are obligate biotrophs belonging to Peronosporales but have different pathological profiles. Despite the economic importance of diseases caused by both Plasmopara, genomic resources are very limited and their effector repertoire is unknown. In this study parallel transcriptome sequencing of P. halstedii and P. viticola was performed, and a Plasmopara species cDNA database (PlasmoparaSp) released containing 46 000 clusters. In oomycetes, two classes of effectors are translocated into the host cytoplasm, the RXLRs and the CRNs. The PlasmoparaSp database was screened in order to identify the repertoire of expressed effectors used by both Plasmopara species; about 50 putative RXLR and 60 CRN were identified for each. These effectors were compared within both species and with seven publicly available oomycete species representative of Peronosporales and Albuginales. Sequence analyses revealed the presence of 55 RXLR families, 12 of them shared by both Plasmopara, and 19 showing amino acid conservation with predicted peptides from at least one oomycete species. Analyses of Plasmopara spp. CRN C-terminal variable regions revealed sequence conservation inside Plasmopara spp. and across oomycetes, with the exception of Hyaloperonospora arabidopsidis. Finally, the analyses confirmed the presence of eight CRN C-terminal domains described in Phytophthora infestans and identified CRN effectors showing similarity to serine proteases. Species-specific effectors were identified that may be involved in host specificity, as well as effectors conserved among oomycetes that might play important roles in the pathogen biology. [ABSTRACT FROM AUTHOR]

Sweet basil ( Ocimum basilicum) is an annual herb crop grown in polyethylene-covered structures in Israel. It is Israel's leading herb crop, grown in warm regions of the country. Downy mildew (caused by Peronospora belbahrii) is a severe disease in Israel and in many other crop-growing regions worldwide. Experiments were carried out to identify potential climate-management techniques for suppression of this disease on basil in non-heated greenhouses. Disease severity was evaluated under commercial-like conditions in three experiments, with 8-10 walk-in tunnels at each location. Pathogen inoculum was introduced into all walk-in tunnels. Regression analysis was performed between the disease values and air temperature, relative humidity ( RH) and soil temperature. Downy mildew severity was negatively related to high (>25°C) air temperature, RH in the range of 65-85% and high (>21°C) soil temperature. The increase in air temperature did not result in a significant increase in leaf temperature; canopy surface median temperatures only reached 30°C. Symptomless plants from relatively warmer tunnels (peak temperatures of 45-48°C) that were transferred to conditions that promote downy mildew (22 ± 2°C, RH > 95%) became severely diseased, showing sporulation of P. belbahrii, suggesting that infection occurred but at the high temperatures symptom expression/tissue colonisation was suppressed. Pot experiments in which aerial and subterranean plant organs were differentially heated revealed that treating the roots with a high temperature (26-31°C), similar to the soil temperatures in the warmer greenhouses, while maintaining the upper plant parts at ambient temperature (20°C), suppresses canopy downy mildew. The effect lasted for 1-2 weeks after the plants were removed from the heated soil treatments and maintained under optimal conditions for pathogen development. Furthermore, oospores were found in the symptomatic leaves. Oospores are minimally affected by high temperature, and therefore the high temperature presumably did not affect pathogen survival. In conclusion, the effect of high greenhouse temperature on basil downy mildew may not result from a direct negative effect of high temperature on the pathogen but from an indirect high-temperature effect on the host, rendering it less susceptible to pathogen development. [ABSTRACT FROM AUTHOR]

There is a widespread recognition that above- and below-ground organisms are linked through their interactions with host plants that span terrestrial subsystems. In addition to direct effects on plants, soil organisms such as root herbivores can indirectly alter interactions between plants and other community members, with potentially important effects on plant growth and fitness., We manipulated root herbivory by Acalymma vittatum in Cucumis sativus to determine indirect effects on arbuscular mycorrhizal fungi, leaf herbivory, the leaf pathogen downy mildew and pollinators. We also manipulated pollen receipt by plants to determine whether root herbivory reduced plant reproduction through changes in pollinator visitation., Overall, root herbivory had strong net negative effects on plant growth and fitness, with 34% reductions in both leaf and fruit production by high root damage levels relative to control, despite reduced infection by downy mildew. High root herbivory also reduced floral visitation by 39%, apparently due to lower flower production, as flower size and scent were unaffected. Above-ground herbivory was not affected by root herbivores., Although root herbivory reduced pollinator visits, pollen receipt manipulations had no effect on fruit set, indicating that reduced pollinator service did not affect plant reproduction., Synthesis. Root herbivory had indirect effects on a range of community members, including mutualists and antagonists both above- and below-ground. Although reduced pathogen infection associated with root herbivory would be expected to benefit plants, root herbivory had an overall strong negative effect on plant growth and reproduction, indicating that direct negative effects over-rode any potential indirect benefits. [ABSTRACT FROM AUTHOR]

BACKGROUND: The level of sensibility towards cymoxanil was quantified by oospore germination assays in 28 populations of Plasmopara viticola (Berk. et Curt.) Berlese and De Toni sampled from different Italian regions from 2009 to 2012. RESULTS: The populations showed good sensitivity levels, with EC50 values often lower than 10mg AI L-1 and percentages of resistant individuals lower than 16%. Only three populations, sampled at the end of the 2012 grapevine growing season, were characterised by high resistance levels. Field trials carried out in two of these vineyards showed that, at the beginning of the 2013 grapevine growing season, the EC50 values of P. viticola populations as measured in the sporangial assaywere higher than those observedwith oospores. At the end of the season, inplots where cymoxanilwas not applied, the populations fully reverted to sensitivity, while the EC50 values remained high where 3-6 applications were performed. CONCLUSION: Oospore germination assays provide valuable information on the sensitivity of populations in vineyards also at the quantitative level. The results obtained during the grapevine growing season confirm those obtained on the oospores, and that cymoxanil resistance is unstable, indirectly suggesting that the application of the fungicide according to antiresistance strategies can lead to good disease control. [ABSTRACT FROM AUTHOR]

BACKGROUND: The level of sensibility towards cymoxanil was quantified by oospore germination assays in 28 populations of Plasmopara viticola (Berk. et Curt.) Berlese and De Toni sampled from different Italian regions from 2009 to 2012. RESULTS: The populations showed good sensitivity levels, with EC50 values often lower than 10 mg AI L-1 and percentages of resistant individuals lower than 16%. Only three populations, sampled at the end of the 2012 grapevine growing season, were characterised by high resistance levels. Field trials carried out in two of these vineyards showed that, at the beginning of the 2013 grapevine growing season, the EC50 values of P. viticola populations as measured in the sporangial assay were higher than those observed with oospores. At the end of the season, in plots where cymoxanil was not applied, the populations fully reverted to sensitivity, while the EC50 values remained high where 3-6 applications were performed. CONCLUSION: Oospore germination assays provide valuable information on the sensitivity of populations in vineyards also at the quantitative level. The results obtained during the grapevine growing season confirm those obtained on the oospores, and that cymoxanil resistance is unstable, indirectly suggesting that the application of the fungicide according to antiresistance strategies can lead to good disease control. [ABSTRACT FROM AUTHOR]

Downy mildew, inflicted by Peronospora sparsa, causes yield losses in arctic bramble ( Rubus arcticus ssp. arcticus), boysenberry ( Rubus spp. hybrid) and blackberry ( Rubus fruticosus), and is a serious threat to the cultivation. Arctic bramble is a high-value crop but its commercial potential is not realisable partly due to downy mildew. Although P. sparsa has been associated with yield losses in arctic bramble, this has not been experimentally proven, nor have the downy mildew symptoms in arctic bramble fruits been described in a controlled experiment. In this study, downy mildew was found to affect the fruits and reduce the yield of arctic bramble. There was a direct correlation between the number of infected leaves and hard fruits resulting from the infection. Owing to the new pesticide legislation in the European Union, it is important to find alternatives to fungicides in the control of downy mildew. The products ALIETTE (fungicide), PHOSFIK (leaf fertiliser) and BION (pathogen defence elicitor) were effective in downy mildew control, Aliette and Phosfik being more effective than Bion especially in preventing yield losses. No arctic bramble cultivars known to be resistant to downy mildew are available. Evaluation of cultivars Alli, Mesma and Pima in the field showed that Mesma is more resistant to downy mildew than are Alli and Pima. Currently the main cultivar grown in Finland, Pima, was the most susceptible variety. The results of this study suggest that the yields and profitability of arctic bramble production could be improved by selecting more resistant varieties, combined with the application of agrochemicals that can suppress the development of downy mildew. [ABSTRACT FROM AUTHOR]

The most economically important diseases of grapevine cultivation worldwide are caused by the fungal pathogen powdery mildew ( Erysiphe necator syn. Uncinula necator) and the oomycete pathogen downy mildew ( Plasmopara viticola). Currently, grapegrowers rely heavily on the use of agrochemicals to minimize the potentially devastating impact of these pathogens on grape yield and quality. The wild North American grapevine species Muscadinia rotundifolia was recognized as early as 1889 to be resistant to both powdery and downy mildew. We have now mapped resistance to these two mildew pathogens in M. rotundifolia to a single locus on chromosome 12 that contains a family of seven TIR- NB- LRR genes. We further demonstrate that two highly homologous (86% amino acid identity) members of this gene family confer strong resistance to these unrelated pathogens following genetic transformation into susceptible Vitis vinifera winegrape cultivars. These two genes, designated resistance to U ncinula necator ( Mr RUN1) and resistance to P lasmopara viticola ( Mr RPV1) are the first resistance genes to be cloned from a grapevine species. Both Mr RUN1 and Mr RPV1 were found to confer resistance to multiple powdery and downy mildew isolates from France, North America and Australia; however, a single powdery mildew isolate collected from the south-eastern region of North America, to which M. rotundifolia is native, was capable of breaking Mr RUN1-mediated resistance. Comparisons of gene organization and coding sequences between M. rotundifolia and the cultivated grapevine V. vinifera at the Mr RUN1/ Mr RPV1 locus revealed a high level of synteny, suggesting that the TIR- NB- LRR genes at this locus share a common ancestor. [ABSTRACT FROM AUTHOR]

Downy mildew ( DM), caused by Pseudoperonospora cubensis (Berk. & M.A. Curtis) Rostovzev, is a worldwide major disease of cucumbers ( Cucumis sativus L.). By screening 10 introgression lines ( ILs) derived from interspecific hybridization between cucumber and the wild Cucumis, C. hystrix, through a whole plant assay, one introgression line ( IL52) was identified with high DM-resistance. IL52 was further used as a resistant parent to make an F2 population with 'changchunmici' (susceptible parent). The F2 population (300 plants) was investigated for DM-yellowing, DM-necrosis and DM-resistance in the adult stage. A genetic map spanning 642.5 cM with 104 markers was constructed and used for QTL analysis from the population. Three QTL regions were identified on chromosome 5 and chromosome 6. By interval mapping analysis, two QTLs for DM-resistance were determined on chromosome 5 (DM_5.1 and DM_5.2), which explained 17.9% and 14.2% of the variation, respectively. QTLs for DM-yellowing were in the same regions as DM-resistance. For DM-necrosis, by interval mapping analysis, one QTL was determined on chromosome 5 (Necr_5.1) that explained 18.3% of the variation and one on chromosome 6 (Necr_6.1) that explained 13.9% of the variation. Our results indicated that the identification of molecular markers linked to the QTLs could be further applied for marker-assisted selection ( MAS) of downy mildew resistance in cucumber. [ABSTRACT FROM AUTHOR]

Most natural Arabidopsis thaliana accessions are susceptible to one or more isolates of the downy mildew pathogen Hyaloperonospora arabidopsidis ( Hpa). However, Arabidopsis C24 has proved resistant to all Hpa isolates tested so far. Here we describe the complex genetic basis of broad-spectrum resistance in C24., The genetics of C24 resistance to three Hpa isolates was analyzed by segregation analysis and quantitative trait locus ( QTL) mapping on recombinant inbred and introgression lines., Resistance of C24 to downy mildew was found to be a multigenic trait with complex inheritance. Many identified resistance loci were isolate-specific and located on different chromosomes. Among the C24 resistance QTLs, we found dominant, codominant and recessive loci. Interestingly, none of the identified loci significantly contributed to resistance against all three tested Hpa isolates., Our study demonstrates that broad-spectrum resistance of Arabidopsis C24 to Hpa is based on different combinations of multiple isolate-specific loci. The identified quantitative resistance loci are particularly promising as they provide an important basis for the cloning of susceptibility- and immunity-related genes. [ABSTRACT FROM AUTHOR]

A cDNA library was constructed from field pea leaves infected by the downy mildew pathogen, Peronospora viciae f. sp. pisi, using a suppression subtractive hybridisation approach. The library consists of 399 expressed sequence tags, from which 207 unisequences were obtained after sequence assembly. Of the unisequences, six were shown to be of Peronospora viciae f. sp. pisi origin. The remaining unisequences were subjected to gene ontology analysis and their functions were predicted in silico. Eleven of these unisequences (representing 24 clones) shared significant sequence similarities with Arabidopsis genes known to be involved in downy mildew resistance, including the well-characterised genes RPP5, RPP6 and RPP27. Expression analysis of five selected unisequences by real-time PCR indicated that all five were up-regulated during downy mildew pathogenesis, suggesting a significant role for these genes in the host response to downy mildew infection. [ABSTRACT FROM AUTHOR]

With 2 figures and 1 table Abstract We have previously constructed a genetic map of Brassica oleracea L. containing the Pp523 locus that confers downy mildew resistance to adult plants. In this work, 44 SSR markers of reference for the Brassica C genome chromosomes were added to the map, allowing the nine major linkage groups to be assigned to the nine chromosomes of B. oleracea. Locus Pp523 was located on chromosome C8, and a locus determining flower colour was mapped to chromosome C3. In comparison with the first version of the map, the new map is denser and more compact. The available genomic information on B. oleracea was enriched with the chromosome location of two phenotypic traits and 421 DNA markers (RAPD, ISSR, AFLP, SCAR, BAC-end derived STS, SSR and other PCR markers). Conversely, the genomic information on B. oleracea chromosome C8 is being used as an additional tool for the map-based cloning of Pp523, the first gene for adult plant resistance to downy mildew precisely located to a specific chromosome of this crop species. [ABSTRACT FROM AUTHOR]

To determine the effects of solar radiation on the survival of sporangia of Pseudoperonospora cubensis, the cause of cucurbit downy mildew, detached sporangia of P. cubensis were either exposed to the sun or placed in the shade from 08·00 to 17·00 h on sunny and cloudy days at Raleigh, North Carolina, in experiments conducted weekly from 9 July to 8 October 2008. Sporangia were assessed for germination every hour following exposure and germination was normalized based on the germination percentage of unexposed sporangia from the same collection. Exposure for a 9-h period, either in the sun or in the shade, significantly ( P < 0·0001) reduced normalized germination of sporangia. Decrease in normalized germination was significantly ( P < 0·0001) higher for sporangia exposed to the sun than sporangia in the shade, with the decrease being more rapid on sunny days than on cloudy days. On sunny days, solar radiation strongly reduced germination of sporangia ( β = −3·51), whilst on cloudy days, reduction in germination of sporangia was minimal ( β = −0·77). On sunny days, an exponential decay model, y = 95·2exp(−0·10 x), provided a significant ( R2 = 75·4%, n = 81, P < 0·0001) quantitative description of the effect of solar radiation dose on the percentage of normalized germination of sporangia. The effective cumulative solar radiation dose to inactivate 95% of the sporangia on sunny days was 29·5 MJ m−2. Disease severity data from inoculation experiments using sporangia exposed to varying amounts of cumulative solar radiation doses corroborated the results of the solar radiation experiments. [ABSTRACT FROM AUTHOR]

The aim of this study was to observe the lipid peroxidation (LP) of cell membranes and antioxidant systems in response to inoculation of Peronospora arborescens causing downy mildew (DM) in opium poppy. Contents of the LP product, malondialdehyde (MDA) and antioxidant glutathione (GSH) were determined in leaves of two opium poppy genotypes, Pps-1 (highly resistant to DM) and Jawahar-16 (highly susceptible to DM) at different time intervals after inoculation (12 h, 24 h, 48 h and 72 h). The provided GSH content corresponded to that of total non-protein sulfhydryl groups. In leaves of Jawahar-16, a significant decrease in concentration of GSH and a persistent increase in concentration of MDA were recorded after inoculation in comparison to leaves of control plants. The continuous decrease in GSH content contributed to damage of cell membranes leading to disease development in Jawahar-16. On the other hand in a resistant genotype (Pps-1), initially at 12 h after inoculation (hai) the level of GSH was found to be high, but a transient and highly significant decrease in content of GSH and increase in content of MDA was observed at 24 hai in comparison to control plants of same genotype and also in comparison to inoculated plants of susceptible genotype (Jawahar-16). These results indicate that generation of GSH and MDA is negatively correlated during the infection process as found in the case of DM-resistant genotype Pps-1 at 24hai, which also suggests an increased need by the host plant for oxidative stress, required for hypersensitive response mediated defense mechanism. [ABSTRACT FROM AUTHOR]

The article presents a study which examines the relationship between Danish and Andean Peronospora farinosa isolates from quinoa, a seed crop which originated from Bolivia and Peru. The study extracted DNA samples from 24 Danish isolates and 16 Andean isolates collected during the 2001 and 2002 seasons and used universally primed-polymerase chain reaction (UC-PCR) amplification to compare their genotypic variation. Results show that the Danish and Andean isolates are distinct from each other.