scholarly journals Comparative Physical Modes of Action of Azoxystrobin, Mancozeb, and Metalaxyl Against Plasmopara viticola (Grapevine Downy Mildew)

Plant Disease ◽  
2001 ◽  
Vol 85 (6) ◽  
pp. 649-656 ◽  
Author(s):  
Francis P. Wong ◽  
Wayne F. Wilcox
Keyword(s):  
Disease Control ◽  
Leaf Surface ◽  
Disease Incidence ◽  
Plasmopara Viticola ◽  
Lower Leaf Surface ◽  
Complete Control ◽  
Grapevine Downy Mildew ◽  
Modes Of Action ◽  
Vapor Activity ◽  
Colony Area

The physical modes of action of azoxystrobin, mancozeb, and metalaxyl were evaluated on grapevine seedlings using Plasmopara viticola as a model pathogen. The protectant, postinfection, postsymptom, translaminar, and vapor activities of azoxystrobin were evaluated at a rate of 250 μg/ml. Azoxystrobin provided 100% disease control when applied 1 to 5 days before inoculation. Postinfection applications of azoxystrobin had little effect on the incidence of disease, but colony area and sporulation from the resultant lesions was reduced by 47 and 96%, respectively, relative to the check treatment when applied up to 5 days after inoculation. Postsymptom applications (6 days after inoculation) of azoxystrobin resulted in an 85% mean reduction of resporulation from diseased tissue relative to the check when seedlings were evaluated 1 to 14 days after treatment. Translaminar activity was greatest when the upper surface of the leaf was treated 7 days before inoculation of the lower leaf surface (94% disease control). In contrast, control was <50% when leaves were similarly inoculated 1 and 3 days after treatment. Vapor activity was not pronounced, providing maximum reductions of 5, 11, and 37%, with regard to incidence, colony area, and sporulation, relative to the check when seedlings were treated 1 to 7 days before inoculating adjacent, untreated leaves. Comparatively, mancozeb (1,790 μg/ml) provided complete control of the disease when applied 1 to 5 days before inoculation, but showed little postinfection activity in reducing disease incidence, although it exhibited moderate to high antisporulant activity when applied in postinfection and postsymptom modes (mean reductions of 38 and 89%, respectively, compared with the check treatments). Metalaxyl (260 μg/ml) also provided complete control of the disease when used in protectant mode, and also when applied 1 day after inoculation. Applications at 3 to 5 days after inoculation provided substantial reductions in disease severity and sporulation (mean reductions of 46 and 94%, respectively, compared with the check treatments), and postsymptom applications resulted in a mean 84% reduction in resporulation. Collectively, the results of this study illustrate the unique physical modes of action for azoxystrobin in comparison to that of two traditional protectant and systemic fungicides, and provide information on how azoxystrobin and other strobilurin fungicides with similar physical modes of action should be best used in disease management programs.

scholarly journals Salvia officinalis Extract Can Protect Grapevine Against Plasmopara viticola

Plant Disease ◽  
2010 ◽  
Vol 94 (5) ◽  
pp. 575-580 ◽  
Author(s):  
Silvia Dagostin ◽  
Tiziano Formolo ◽  
Oscar Giovannini ◽  
Ilaria Pertot ◽  
Annegret Schmitt
Keyword(s):  
Disease Control ◽  
Downy Mildew ◽  
Disease Incidence ◽  
Plasmopara Viticola ◽  
Salvia Officinalis ◽  
Promising Alternative ◽  
Rainy Period ◽  
Grapevine Downy Mildew ◽  
Progress Curve ◽  
High Level

The ability of sage (Salvia officinalis) extract to control grapevine downy mildew under greenhouse and field conditions was tested. The persistence and rainfastness of sage extract were also investigated. Sage extract provided a high level of sustained disease control in artificially inoculated, potted grapevine under greenhouse conditions. However, even small amounts of simulated rainfall (10 mm) significantly reduced efficacy of sage extract. In a field experiment in 2006, sage extract provided 94% reduction in disease incidence and 63% reduction in area under the disease progress curve for disease severity on berries and leaves, respectively, reaching a level of disease control not significantly different from that provided by copper hydroxide. In 2007, the sage extract provided only a partial reduction (less than 30%) of downy mildew on leaves, probably as a result of a long rainy period between two of the consecutive treatments. Overall, sage extract effectively controlled grapevine downy mildew and could be a promising alternative to copper in organic viticulture. However, the low rainfastness of this treatment adversely affected its efficacy.

scholarly journals Distribution of Baseline Sensitivities to Azoxystrobin Among Isolates of Plasmopara viticola

Plant Disease ◽  
2000 ◽  
Vol 84 (3) ◽  
pp. 275-281 ◽  
Author(s):  
Francis P. Wong ◽  
Wayne F. Wilcox
Keyword(s):  
New York ◽  
Disease Severity ◽  
Disease Incidence ◽  
Leaf Disc ◽  
Plasmopara Viticola ◽  
Grapevine Downy Mildew ◽  
Coefficients Of Variation ◽  
Control Versus ◽  
Strobilurin Fungicide ◽  
Effective Doses

An excised leaf disc assay was developed for determining the sensitivity of isolates of Plasmopara viticola (causal agent of grapevine downy mildew) to the strobilurin fungicide azoxystrobin. Five repeated assays with the same five single-sporangiophore isolates showed that the technique yielded reproducible results; that is, coefficients of variation ranged from 4.0 to 20% (mean 12%) for effective doses for 50% control (ED50 values) based on disease incidence and from 4.4 to 14% (mean 8.1%) for ED50 values based on disease severity. Then, the assay was applied to 81 single-sporangiophore isolates of P. viticola collected from 10 geographically distinct vineyards in western New York, providing a baseline distribution of sensitivities within this population. For disease incidence, individual ED50 values ranged from 0.05 to 0.94 μg/ml (mean 0.40 μg/ml), whereas for disease severity they ranged from 0.04 to 0.78 μg/ml (mean 0.24 μg/ml). When 61 of these isolates were similarly tested at a single discriminatory dose of 0.50 μg/ml, azoxystrobin provided 61% control of disease incidence versus 41 and 1.1% control for trifloxystrobin and kresoximmethyl, respectively; for disease severity (colony diameter), azoxystrobin provided 80% control versus 57 and 1.1% control for trifloxystrobin and kresoximmethyl, respectively. These results provide information that can be utilized in future monitoring of P. viticola resistance to azoxystrobin and indicate differences in the intrinsic activities of the three strobilurin fungicides against this pathogen.

scholarly journals Vapor Activity and Systemic Movement of Mefenoxam Control Grapevine Downy Mildew

Plant Disease ◽  
2007 ◽  
Vol 91 (10) ◽  
pp. 1260-1264 ◽  
Author(s):  
Megan M. Kennelly ◽  
David M. Gadoury ◽  
Wayne F. Wilcox ◽  
Robert C. Seem
Keyword(s):  
Downy Mildew ◽  
Leaf Tissue ◽  
Plasmopara Viticola ◽  
Post Inoculation ◽  
Complete Suppression ◽  
Stem Tissue ◽  
Grapevine Downy Mildew ◽  
Systemic Movement ◽  
Closed Systems ◽  
Vapor Activity

Metalaxyl is translocated from roots to leaves to control a number of oomycete pathogens, but systemic movement from vegetative organs into fruit and vapor activity against Plasmopara viticola, the causal agent of grapevine downy mildew, has not been examined experimentally. We inoculated fruit clusters of grapevines with P. viticola at prebloom, bloom, or 1 week postbloom. We then selectively applied mefenoxam (288 mg/liter), the active enantiomer of metalaxyl, to the leaves or stem tissue 12 to 48 h after inoculation. Little to no downy mildew developed on fruit when mefenoxam was applied to leaf tissue, stem tissue, or both. In contrast, downy mildew symptoms were severe on inoculated clusters on untreated shoots. When potential vapor activity was blocked, we observed fungicidal activity on seedling foliage in response to apparent systemic movement from treated stems and soil, but not from leaves. However, when vapor activity was permitted, mefenoxam residues on treated leaves controlled disease on other, untreated leaves. In subsequent vineyard experiments, vapor and systemic activity provided equivalent and near-complete suppression of downy mildew on clusters 48 h post inoculation. Furthermore, inoculated grape seedlings that were placed near mefenoxam-treated seedlings in open and closed systems developed nil to trace levels of downy mildew compared with controls, further indicating that the material has strong vapor activity.

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

2022 ◽  
Vol 12 ◽  
Author(s):  
Ying Wang ◽  
Xiao Cao ◽  
Yulei Han ◽  
Xing Han ◽  
Zhilei Wang ◽  
...  
Keyword(s):  
Plant Defense ◽  
Downy Mildew ◽  
Leaf Surface ◽  
Plasmopara Viticola ◽  
Defense Responses ◽  
Management Program ◽  
Oxidative Enzymes ◽  
Grapevine Downy Mildew ◽  
Protected Plants ◽  
Grapevine Leaves

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

scholarly journals Plasmopara obducens: A new threat to the production of Impatiens Walleriana in Serbia

2011 ◽  
Vol 26 (1) ◽  
pp. 43-53 ◽  
Author(s):  
Danijela Ristic ◽  
Ana Vucurovic ◽  
Ivana Stankovic ◽  
Jelena Jovic ◽  
Katarina Milojevic ◽  
...  
Keyword(s):  
Downy Mildew ◽  
Nuclear Dna ◽  
Leaf Surface ◽  
Disease Incidence ◽  
Ribosomal Subunit ◽  
Lsu Rdna ◽  
Lower Leaf Surface ◽  
Pathogenicity Tests ◽  
Impatiens Walleriana ◽  
Phytosanitary Measures

During 2010, Impatiens walleriana plants with symptoms of downy mildew were collected in a greenhouse in the vicinity of Mionica, Kolubara District. Disease incidence was extremely high, approaching 100%, and wilting and collapse of affected plants was very rapid, resulting in losses of more than 90%. White downy growth produced on the lower leaf surface consisted of hyaline, thin-walled sporangiophores with monopodial branching and numerous, ovoid and hyaline sporangia. Apical branchlets of sporangiophores were at right angles to the main axis, with no apical thickening. Pathogenicity tests included inoculation of young I. walleriana plants by spraying with a sporangial suspension, and downy mildew symptoms were observed after 13 to 15 days. The absence of well-defined spots on the infected impatiens leaves and straight sporangiophores indicated that the pathogen was P. obducens, which was further supported by molecular identification, the 5?-end of the nuclear DNA coding for the large ribosomal subunit (LSU rDNA) was amplified by PCR, using primers NL1 and NL4. A representative isolate, 28-10, was sequenced and phylogenetic analysis showed its grouping with other P. obducens isolates of different origin. Considering that impatiens downy mildew in Serbia is proved to be caused by P. obducens it is necessary to employ adequate phytosanitary measures to prevent further spread of the pathogen.

scholarly journals Evaluation of a Warning System for Controlling Primary Infections of Grapevine Downy Mildew

Plant Disease ◽  
2010 ◽  
Vol 94 (6) ◽  
pp. 709-716 ◽  
Author(s):  
T. Caffi ◽  
V. Rossi ◽  
R. Bugiani
Keyword(s):  
Disease Incidence ◽  
Warning System ◽  
Plasmopara Viticola ◽  
Short Message ◽  
Short Term ◽  
Infection Period ◽  
Grapevine Downy Mildew ◽  
Weather Forecasts ◽  
Short Message System ◽  
Message System

A warning system based on (i) a model that simulates the development of all cohorts of Plasmopara viticola oospores, from oospore germination to infection; (ii) short-term weather forecasts; and (iii) a mobile phone short message system was tested in Northern Italy, from 2006 to 2008. An unsprayed control was compared with a “Warning A” treatment (WA, fungicides were applied whenever the warning system predicted an infection period), a “Warning B” treatment (WB, fungicides were applied as in the WA treatment but only when the relative dimension of any oospore cohort predicted by the model exceeded a threshold), and a “grower” treatment (fungicides were applied according to a conventional schedule). Average disease incidence on leaves was reduced by up to 90% in sprayed plots compared with unsprayed plots. On bunches, efficacy was always >90% at fruit set; when most berries were touching, efficacy was higher for the WA (96%) than for grower (89%) and WB (85%) treatments. On average, 6.8 fungicide sprays were applied following the grower's schedule; use of the warning system reduced applications by about one-half (WA treatment) or two-thirds (WB treatment). The grower's schedule had an average cost of 337 €/ha; the average saving with the WA and the WB treatments was 174 and 224 €/ha, respectively.

scholarly journals A High-Quality Grapevine Downy Mildew Genome Assembly Reveals Rapidly Evolving and Lineage-Specific Putative Host Adaptation Genes

2019 ◽  
Vol 11 (3) ◽  
pp. 954-969 ◽  
Author(s):  
Yann Dussert ◽  
Isabelle D Mazet ◽  
Carole Couture ◽  
Jérôme Gouzy ◽  
Marie-Christine Piron ◽  
...  
Keyword(s):  
Downy Mildew ◽  
Genome Assembly ◽  
Population Genomics ◽  
Plasmopara Viticola ◽  
Plant Diseases ◽  
Host Specialization ◽  
Grapevine Downy Mildew ◽  
Downy Mildews ◽  
Genes Encoding ◽  
High Level

Abstract Downy mildews are obligate biotrophic oomycete pathogens that cause devastating plant diseases on economically important crops. Plasmopara viticola is the causal agent of grapevine downy mildew, a major disease in vineyards worldwide. We sequenced the genome of Pl. viticola with PacBio long reads and obtained a new 92.94 Mb assembly with high contiguity (359 scaffolds for a N50 of 706.5 kb) due to a better resolution of repeat regions. This assembly presented a high level of gene completeness, recovering 1,592 genes encoding secreted proteins involved in plant–pathogen interactions. Plasmopara viticola had a two-speed genome architecture, with secreted protein-encoding genes preferentially located in gene-sparse, repeat-rich regions and evolving rapidly, as indicated by pairwise dN/dS values. We also used short reads to assemble the genome of Plasmopara muralis, a closely related species infecting grape ivy (Parthenocissus tricuspidata). The lineage-specific proteins identified by comparative genomics analysis included a large proportion of RxLR cytoplasmic effectors and, more generally, genes with high dN/dS values. We identified 270 candidate genes under positive selection, including several genes encoding transporters and components of the RNA machinery potentially involved in host specialization. Finally, the Pl. viticola genome assembly generated here will allow the development of robust population genomics approaches for investigating the mechanisms involved in adaptation to biotic and abiotic selective pressures in this species.

scholarly journals First Insights into the Effect of Mycorrhizae on the Expression of Pathogen Effectors during the Infection of Grapevine with Plasmopara viticola

2021 ◽  
Vol 13 (3) ◽  
pp. 1226
Author(s):  
Ana Cruz-Silva ◽  
Andreia Figueiredo ◽  
Mónica Sebastiana
Keyword(s):  
Mycorrhizal Fungi ◽  
Arbuscular Mycorrhizal ◽  
Plasmopara Viticola ◽  
Vitis Vinifera L ◽  
Wine Production ◽  
Grapevine Downy Mildew ◽  
Pathogen Effectors ◽  
Rxlr Effectors ◽  
Mycorrhizal Inoculation ◽  
And Control

Grapevine (Vitis vinifera L.), widely used for berry and wine production, is highly susceptible to the pathogenic oomycete Plasmopara viticola, the etiological agent of grapevine downy mildew disease. The method commonly used to prevent and control P. viticola infection relies on multiple applications of chemical fungicides. However, with European Union goals to lower the usage of such chemicals in viticulture there is a need to develop new and more sustainable strategies. The use of beneficial microorganisms with biocontrol capabilities, such as the arbuscular mycorrhizal fungi (AMF), has been pointed out as a viable alternative. With this study, we intended to investigate the effect of AMF colonization on the expression of P. viticola effectors during infection of grapevine. Grapevine plants were inoculated with the AMF Rhizophagus irregularis and, after mycorrhizae development, plants were infected with P. viticola. The expression of P. viticola RxLR effectors was analyzed by real-time PCR (qPCR) during the first hours of interaction. Results show that pre-mycorrhizal inoculation of grapevine alters the expression of several P. viticola effectors; namely, PvRxLR28, which presented decreased expression in mycorrhizal plants at the two time points post-infection tested. These results suggest that the pre-inoculation of grapevine with AMF could interfere with the pathogen’s ability to infect grapevine by modulation of pathogenicity effectors expression, supporting the hypothesis that AMF can be used to increase plant resistance to pathogens and promote more sustainable agriculture practices, particularly in viticulture.

scholarly journals Vaccine refusal and the endgame: walking the last mile first

2013 ◽  
Vol 368 (1623) ◽  
pp. 20120148 ◽  
Author(s):  
Diane S. Saint-Victor ◽  
Saad B. Omer
Keyword(s):  
Disease Control ◽  
Disease Incidence ◽  
Target Population ◽  
Special Issue ◽  
Disease Eradication ◽  
Vaccine Refusal ◽  
Last Mile ◽  
Low Levels

As multiple papers within this special issue illustrate, the dynamics of disease eradication are different from disease control. When it comes to disease eradication, ‘the last mile is longest’. For social and ecological reasons such as vaccine refusal, further ending incidence of a disease when it has reached low levels is frequently complex. Issues of non-compliance within a target population often influence the outcome of disease eradication efforts. Past eradication efforts confronted such obstacles towards the tail end of the campaign, when disease incidence was lowest. This article provides a comparison of non-compliance within polio, measles and smallpox campaigns, demonstrating the tendency of vaccine refusal to rise as disease incidence falls. In order to overcome one of the most intractable challenges to eradication, future disease eradication efforts must prioritize vaccine refusal from the start, i.e. ‘walk the last mile first’.

Ectopic growth of the fungal symbiont (Chaetothyriales) on Ipomoea carnea

Botany ◽  
2021 ◽  
Author(s):  
Aziza Ibrahim Noor ◽  
Amy Nava ◽  
Marwa Neyaz ◽  
Peter Cooke ◽  
Rebecca Creamer ◽  
...  
Keyword(s):  
Cross Sections ◽  
Storage Disease ◽  
Growth Habit ◽  
Leaf Surface ◽  
Livestock Grazing ◽  
Lysosomal Storage ◽  
Lower Leaf Surface ◽  
Ipomoea Carnea ◽  
Show Evidence ◽  
Glycoprotein Processing

Swainsonine, an indolizidine alkaloid, is an alpha-mannosidase and mannosidase II inhibitor that alters glycoprotein processing and causes lysosomal storage disease. Swainsonine is the toxic principle in several plant species worldwide and causes severe toxicosis in livestock grazing these plants. All swainsonine-containing plant taxa investigated to date are associated with fungal symbionts that produce swainsonine. Among the swainsonine-containing convolvulaceous species, Ipomoea carnea is associated with a seed transmitted symbiont belonging to the fungal order Chaetothyriales. The nature of this association was unclear therefore this association was investigated further using microscopy. Macroscopic and microscopic data reported here demonstrate that the Chaetothyriales symbiont associated with I. carnea grows ectopically on the adaxial (upper) surface of leaves as lacy mycelia in plants that contain swainsonine and was not present on plants lacking swainsonine that were derived from fungicide treated seeds. Hyphae were not observed on the surface of any other tissues including the abaxial (lower) leaf surface, petiole, and stem. Mycelia were not visible in internal tissues below the epidermis and there did not appear to be any hyphal extensions within the fibrovascular bundles or stomata. Longitudinal and/or cross sections of the stems or petioles did not show evidence of hyphae growing between cells. These results suggest an epibiotic growth habit of the Chaetothyriales symbiont in association with I. carnea.

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