Agent Of Grapevine Downy Mildew Research Articles

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

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

Peptide analogs of a Trichoderma peptaibol effectively control downy mildew in the vineyard.

Plasmopara viticola, the agent of grapevine downy mildew, causes enormous economic damage and its control is primarily based on synthetic fungicides. The European Union (EU) policies promote reducing reliance on synthetic plant protection products. Biocontrol agents (BCA) such as Trichoderma constitute a resource for the development of biopesticides. Trichoderma species produce secondary metabolites such as peptaibols, whose poor water solubility hampers their practical use as agrochemicals. To identify new bio-inspired molecules effective against P. viticola, some water-soluble peptide analogs of the peptaibol trichogin were synthesized. In grapevine leaf disk assays, various peptides at 50 µM completely prevented P. viticola infection after zoosporangia inoculation. Microscopic observations carried out with one of the most effective peptides showed that it causes membrane lysis and cytoplasm granulation of both zoosporangia and zoospores. Among the effective peptides, 4r was selected for a two-year field trial experiment. In the vineyard, the peptide administered at 100 µM (equivalent to 129.3 g/ha) overall reduced significantly disease incidence and severity on both leaves and bunches, allowing protection levels similar to those obtained with a cupric fungicide. In the second-year trial, reduced dosages were also tested, and results indicated that even by reducing the peptide concentration by 50 or 75%, a significant decrease in the disease level was obtained at the end of the trial. The peptide did not show any phytotoxic effect. Previously, peptide 4r had been demonstrated to be active against other fungal pathogens, including the grapevine fungus Botrytis cinerea. Thus, this peptide may be a candidate for broad-spectrum fungicide whose biological properties deserve further investigation.

The Characterization of Pathotypes in Grapevine Downy Mildew Provides Insights into the Breakdown of Rpv3, Rpv10, and Rpv12 Factors in Grapevines.

We describe a standard method for characterizing the virulence profile of Plasmopara viticola, the causal agent of grapevine downy mildew. We used 33 European strains to inoculate six grapevine varieties carrying the principal factors for resistance to downy mildew (Rpv1, Rpv3.1, Rpv3.2, Rpv5, Rpv6, Rpv10, and Rpv12) and the susceptible Vitis vinifera 'Chardonnay'. For each interaction, we characterized the level of sporulation by image analysis and the intensity of the grapevine hypersensitive response by visual score. We propose a definition for the breakdown of grapevine quantitative resistances combining these two traits. Among the 33 strains analyzed, 28 are virulent on at least one resistance factor. We identified five different pathotypes across the 33 strains analyzed: two pathotypes overcoming a single resistance factor (vir3.1 and vir3.2) and three complex pathotypes overcoming multiple resistance factors (vir3.1,3.2; vir3.2,12; vir3.1,3.2,10). Our findings confirm the widespread occurrence of P. viticola strains overcoming the Rpv3 haplotypes (28 strains). We also detected the first breakdown of resistance to the Rpv10 by a strain from Germany and the breakdown of Rpv12 factors by a strain from Hungary. The pathotyping method proposed here and the associated differential host range lay the groundwork for the early detection of resistance breakdown in grapevines. This approach will also facilitate the monitoring of the evolution of P. viticola populations at large spatial scales. This is an essential step forward to promoting durable management of the resistant grapevine varieties currently available.

First report of oospore formation in Plasmopara viticola, the causal agent of grapevine downy mildew, in highland regions of southern Brazil

AbstractThis work evaluates the formation of oospores of Plasmopara viticola, the causal agent of grape downy mildew (DM), in highland regions in southern Brazil. Leaves of susceptible and resistant grape genotypes naturally infected with the pathogen were collected in the autumn of 2017, 2018, and 2019 from vineyards located in the highlands of Santa Catarina state. Leaf tissues were evaluated by light microscopy and scanning electron microscopy. Oospores of P. viticola were identified in both susceptible and resistant host genotypes. They were concentrated in the central regions of the DM lesions, close to the leaf veins, and exhibited a rounded shape, yellowish colour, thick wall, and a diameter ranging from 16.28 to 49.15 µm. The formation of oospores is strong evidence that sexual reproduction is occurring in P. viticola in the climatic conditions of the highlands of southern Brazil. Sexual reproduction contributes to the maximization of genetic diversity via meiosis. Populations with high genetic variability are more likely to break resistance mechanisms conferred by resistance genes and to develop resistance to fungicides applied for disease control. To our knowledge, this is the first scientific study to prove the formation of P. viticola oospores in Brazil. The results presented provide a solid basis for further studies on sexual recombination in P. viticola. Genetic improvement programmes for grapevines, disease management methods, and disease prediction models need to consider the sexual reproduction of this pathogen, otherwise their effectiveness may be compromised.

The Durability of Quantitative Host Resistance and Variability in Pathogen Virulence in the Interaction Between European Grapevine Cultivars and Plasmopara viticola

European grapevine, Vitis vinifera, carries no major resistances against Plasmopara viticola, the causal agent of grapevine downy mildew. The introgression of quantitative trait loci conferring resistance to P. viticola (Rpv) from American and Asian donor species has resulted in a range of resistant cultivars. In light of the perennial nature of grapevine and the high evolutionary potential of P. viticola, the durability of this quantitative resistance is an important challenge. Durability of host resistance and variability in pathogen virulence may be evaluated by describing interactions between pathogen isolates and grapevine cultivars in terms of Rpv loci. A set of 16 cultivars carrying different combinations of Rpv loci, was challenged with five P. viticola isolates, obtained from susceptible or Rpv3.1+V. vinifera cultivars. Based on the severity of sporulation, different host and pathogen phenotypes might be distinguished, which could be related to the presence of different Rpv loci. The hormonal responses before and during some interactions were compared to assess the resistance mechanisms underlying Rpv3.1, Rpv10, and Rpv12 and the infection mechanisms of the different isolates. This paper reports on the strength of some of the commonly used Rpv loci, single or stacked. The isolates derived from Rpv3.1+ hosts, GREPv1 and GPHPv1, were able to sporulate intensely on cultivars carrying Rpv3.1, without triggering necrosis. Moreover, Rpv10 was not able to efficiently halt the development of the Rpv3.1-breaking isolate GPHPv1. Cultivars carrying Rpv12, however, were resistant to all five P. viticola isolates. Phytohormones might be implicated in the basal resistance against this pathogen, but during the early defense response, no significant hormonal responses to the isolates were observed. The isolate-specificity of the Rpv3- and Rpv10-mediated resistance suggests that these loci do not result in the most sustainable resistance. Furthermore, the isolate-specific behavior of the pathogen emphasizes the need for a characterization system for P. viticola. A standardized phenotyping assay may be used to determine P. viticola pathogen phenotypes or measure the durability, strength, and isolate-specificity of the host quantitative resistances. The characterization of both components of the pathosystem may lead to an increased understanding of the resistance mechanisms, beneficial for a durable deployment of resistance genes.

Decision Support Systems for Downy Mildew (Plasmopara viticola) Control in Grapevine: Short Comparison Review

Plasmopara viticola, the aetiological agent of grapevine downy mildew (DM), is the most important pathology afflicting viticulture and requires a great number of fungicide treatments to avoid severe yield losses and quality decreasing. To date, great efforts have been made to reduce the use of plant defensive products. Resistant cultivars, new agrochemicals and, finally, epidemiological models have been elaborated to better manage plant phytoiatric treatments. Nowadays, models are widely used because they allow the cultivation of traditional varieties, limiting agrochemicals. Using such models, implemented in a DSS (Decision Support System), results in a lower risk of grapevine damage by diseases and pests and, in many cases, in a lower input of active substances. Thanks to the information reported in a DSS, users could become more conscious of the relations between weather conditions, pathogen’s cycle, and infections risk, which is an issue not yet well understood by lots of winegrowers. For this instance, DSSs have been established as important tools for the achievement of more sustainable agricultural practices. Hence, understanding their working principles might be really important. In fact, in this way, technicians and farmers can adopt the suitable system to fit their own agricultural reality, aiming at a better vineyard management under a sustainable point of view.

Fungicide Resistance Evolution and Detection in Plant Pathogens: Plasmopara viticola as a Case Study.

The use of single-site fungicides to control plant pathogens in the agroecosystem can be associated with an increased selection of resistance. The evolution of resistance represents one of the biggest challenges in disease control. In vineyards, frequent applications of fungicides are carried out every season for multiple years. The agronomic risk of developing fungicide resistance is, therefore, high. Plasmopara viticola, the causal agent of grapevine downy mildew, is a high risk pathogen associated with the development of fungicide resistance. P. viticola has developed resistance to most of the fungicide classes used and constitutes one of the most important threats for grapevine production. The goals of this review are to describe fungicide resistance evolution in P. viticola populations and how to conduct proper monitoring activities. Different methods have been developed for phenotyping and genotyping P. viticola for fungicide resistance and the different phases of resistance evolution and life cycles of the pathogen are discussed, to provide a full monitoring toolkit to limit the spread of resistance. A detailed revision of the available tools will help in shaping and harmonizing the monitoring activities between countries and organizations.

Two-omics data revealed commonalities and differences between Rpv12- and Rpv3-mediated resistance in grapevine

Plasmopara viticola is the causal agent of grapevine downy mildew (DM). DM resistant varieties deploy effector-triggered immunity (ETI) to inhibit pathogen growth, which is activated by major resistance loci, the most common of which are Rpv3 and Rpv12. We previously showed that a quick metabolome response lies behind the ETI conferred by Rpv3 TIR-NB-LRR genes. Here we used a grape variety operating Rpv12-mediated ETI, which is conferred by an independent locus containing CC-NB-LRR genes, to investigate the defence response using GC/MS, UPLC, UHPLC and RNA-Seq analyses. Eighty-eight metabolites showed significantly different concentration and 432 genes showed differential expression between inoculated resistant leaves and controls. Most metabolite changes in sugars, fatty acids and phenols were similar in timing and direction to those observed in Rpv3-mediated ETI but some of them were stronger or more persistent. Activators, elicitors and signal transducers for the formation of reactive oxygen species were early observed in samples undergoing Rpv12-mediated ETI and were paralleled and followed by the upregulation of genes belonging to ontology categories associated with salicylic acid signalling, signal transduction, WRKY transcription factors and synthesis of PR-1, PR-2, PR-5 pathogenesis-related proteins.

A spectrophotometric approach for determining sporangium and zoospore viability of Plasmopara viticola

AbstractA 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.

The Nuclear-Localized RxLR Effector PvAvh74 From Plasmopara viticola Induces Cell Death and Immunity Responses in Nicotiana benthamiana.

Downy mildew is one of the most serious diseases of grapevine (Vitis spp). The causal agent of grapevine downy mildew, Plasmopara viticola, is an obligate biotrophic oomycete. Although oomycete pathogens such as P. viticola are known to secrete RxLR effectors to manipulate host immunity, there have been few studies of the associated mechanisms by which these may act. Here, we show that a candidate P. viticola RxLR effector, PvAvh74, induces cell death in Nicotiana benthamiana leaves. Using agroinfiltration, we found that nuclear localization, two putative N-glycosylation sites, and 427 amino acids of the PvAvh74 carboxyl terminus were necessary for cell-death-inducing activity. Using virus-induced gene silencing (VIGS), we found that PvAvh74-induced cell death in N. benthamiana requires EDS1, NDR1, SGT1, RAR1, and HSP90, but not BAK1. The MAPK cascade components MEK2, WIPK, and SIPK were also involved in PvAvh74-induced cell death in N. benthamiana. Transient expression of PvAvh74 could suppress Phytophthora capsici colonization of N. benthamiana, which suggests that PvAvh74 elicits plant immune responses. Suppression of P. capsici colonization also was dependent on nuclear localization of PvAvh74. Additionally, PvAvh74-triggered cell death could be suppressed by another effector, PvAvh8, from the same isolate. This work provides a framework to further investigate the interactions of PvAvh74 and other RxLR effectors with host immunity.

Surfactin and fengycin contribute to the protection of a Bacillus subtilis strain against grape downy mildew by both direct effect and defence stimulation.

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.

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

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.

FUNGITOXICITY OF ESSENTIAL OILS ON PLASMOPARA VITICOLA,CAUSAL AGENT OF GRAPEVINE DOWNY MILDEW

ABSTRACT This study aimed to evaluate the fungitoxic (antifungal) effect of seven essential oils on Plasmopara viticola, the causal agent of grapevine downy mildew. The cinnamon, eucalyptus globulus, marjoram, melaleuca, peppermint, oregano and white thyme essential oils were compared with the mancozeb + metalaxyl-M fungicide. Three experiments were conducted to evaluate the effect of essential oils on spore germination. The first experiment evaluated the effect of direct contact of essential oils on the pathogen; the second evaluated the effect of volatile compounds on the pathogen and the third assessed the behavior of essential oils, when applied to vine leaves in field conditions, on the pathogen. All essential oils inhibited the spores’ germination, but in varying degrees, in addition, presenting fungistatic activity. All the essential oils showed chemical instability when the incubation time or the interval between products application where increased, all oils decrease antifungal activity percentage. Noteworthy, the cinnamon and the eucalyptus globulus essential oils were the most fungitoxic (antifungal) on P. viticola.

Probing the contractile vacuole as Achilles' heel of the biotrophic grapevine pathogen Plasmopara viticola.

The causative agent of Grapevine Downy Mildew, the oomycete Plasmopara viticola, poses a serious threat to viticulture. In the current work, the contractile vacuole of the zoospore is analysed as potential target for novel plant protection strategies. Using a combination of electron microscopy, spinning disc confocal microscopy, and video differential interference contrast microscopy, we have followed the genesis and dynamics of this vacuole required during the search for the stomata, when the non-walled zoospore is exposed to hypotonic conditions. This subcellular description was combined with a pharmacological study, where the functionality of the contractile vacuole was blocked by manipulation of actin, by Na, Cu, and Al ions or by inhibition of the NADPH oxidase. We further observe that RGD peptides (mimicking binding sites for integrins at the extracellular matrix) can inhibit the function of the contractile vacuole as well. Finally, we show that an extract from Chinese liquorice (Glycyrrhiza uralensis) proposed as biocontrol for Downy Mildews can efficiently induce zoospore burst and that this activity depends on the activity of NADPH oxidase. The effect of the extract can be phenocopied by its major compound, glycyrrhizin, suggesting a mode of action for this biologically safe alternative to copper products.

Graphene oxide-Fe3O4 nanocomposites as high-performance antifungal agents against Plasmopara viticola

Plasmopara viticola , a causal agent of grapevine downy mildew, is a widely distributed pathogen, which can cause destructive disease in field-grown grapevines. Although fungicides are used to treat the disease, fungicide-resistant strains have been emerging. In this study, we developed graphene oxide (GO)-Fe3O4 nanocomposites, which could effectively repress the germination of sporangia and inhibit the development of downy mildew. 50 μg mL−1 GO-Fe3O4 showed excellent protective and fungicidal activities. 250 μg mL−1 GO-Fe3O4 on grapevine leaves in the field could significantly decrease the severity of downy mildew, suggesting its potent curative effect. Moreover, GO-Fe3O4 had no significant toxic effects on grapevine plants even at the concentration twice that of the highest dosage (1000 μg mL−1) used in this study. Our work suggested that GO-Fe3O4 would offer an important opportunity to develop new approach for controlling plant diseases.

Soybean and casein hydrolysates induce grapevine immune responses and resistance against Plasmopara viticola.

Plasmopara viticola, the causal agent of grapevine downy mildew, is one of the most devastating grape pathogen in Europe and North America. Although phytochemicals are used to control pathogen infections, the appearance of resistant strains and the concern for possible adverse effects on environment and human health are increasing the search for alternative strategies. In the present investigation, we successfully tested two protein hydrolysates from soybean (soy) and casein (cas) to trigger grapevine resistance against P. viticola. On Vitis vinifera cv. Marselan plants, the application of soy and cas reduced the infected leaf surface by 76 and 63%, as compared to the control, respectively. Since both hydrolysates might trigger the plant immunity, we investigated their ability to elicit grapevine defense responses. On grapevine cell suspensions, a different free cytosolic calcium signature was recorded for each hydrolysate, whereas a similar transient phosphorylation of two MAP kinases of 45 and 49 kDa was observed. These signaling events were followed by transcriptome reprogramming, including the up-regulation of defense genes encoding pathogenesis-related (PR) proteins and the stilbene synthase enzyme responsible for the biosynthesis of resveratrol, the main grapevine phytoalexin. Liquid chromatography analyses confirmed the production of resveratrol and its dimer metabolites, δ- and ε-viniferins. Overall, soy effects were more pronounced as compared to the cas ones. Both hydrolysates proved to act as elicitors to enhance grapevine immunity against pathogen attack.

福岡県におけるQoI 剤耐性ブドウべと病菌の発生と防除対策

近年の福岡県におけるブドウべと病の多発要因を解明するため，基幹薬剤の一つであるQoI 剤の耐性菌検定を実施した。2011年に県内主要産地8ほ場，24罹病葉と2011年と2013年に場内1ほ場14罹病葉について，QoI 剤耐性検定に用いられるPCR-RFLP 法によって，耐性検定を行った。その結果，全葉から耐性菌を示す遺伝子パターンが確認され，県内に広く耐性菌が発生していることが明らかとなった。次に，耐性菌発生ほ場におけるQoI 剤の防除効果の低下とQoI 剤以外の系統薬剤などの発病抑制効果を検討するため，2011年から2013年に場内ほ場で試験を実施した。QoI 剤であるアゾキシストロビン水和剤の防除効果は低く，他系統薬剤のマンゼブ水和剤，ベンチアカリブイソプロピル・マンゼブ水和剤およびマンジプロパミド水和剤の防除効果は高かった。また，卵菌類による病害に対して発病抑制効果があることが知られている亜リン酸肥料も発病を低く抑えた。

Rapid and multiregional adaptation to host partial resistance in a plant pathogenic oomycete: Evidence from European populations of Plasmopara viticola, the causal agent of grapevine downy mildew

Crop pathogens evolve rapidly to adapt to their hosts. The use of crops with quantitative disease resistance is expected to alter selection of pathogen life-history traits. This may result in differential adaptation of the pathogen to host cultivars and, sometimes, to the erosion of quantitative resistance. Here, we assessed the level of host adaptation in an oomycete plant pathogenic species. We analysed the phenotypic and genetic variability of 17 Plasmopara viticola isolates collected on Vitis vinifera and 35 isolates from partially resistant varieties (Regent and genotypes carrying the Rpv1 gene). Cross-inoculation experiments assessed two components of aggressiveness and a life-history trait of the pathogen: disease severity, sporangial production and sporangia size. The results contribute evidence to the emergence of P. viticola aggressive isolates presenting a high level of sporulation on the partially resistant Regent. By contrast, no adaptation to the Rpv1 gene was found in this study. The erosion of Regent resistance may have occurred in less than 5years and at least three times independently in three distant wine-producing areas. Populations from resistant varieties showed a significant increase in sporangia production capacity, indicating an absence of fitness costs for this adaptation. The increase in the number of sporangia was correlated with a reduction in sporangia size, a result which illustrates how partial plant disease resistance can impact selection of the pathogen’s life-history traits. This case study on grapevine downy mildew shows how new plant pathogen populations emerge in agro-ecosystems by adapting to partial host resistance. This adaptive pattern highlights the need for wise management of plant partial disease resistance to ensure its sustainability over time.

Lysobacter capsici AZ78 can be combined with copper to effectively control Plasmopara viticola on grapevine

The bacterial genus Lysobacter represents a still underdeveloped source of biocontrol agents able to protect plants against pathogenic oomycetes. In this work the L. capsici strain AZ78 was evaluated with regard to the biological control of Plasmopara viticola, the causal agent of grapevine downy mildew. L. capsici AZ78 is able to resist copper ions and its resistance to this metal is probably due to the presence of genes coding for copper oxidase (copA) and copper exporting PIB-type ATPases (ctpA). The presence of both genes was also detected in other members of the Lysobacter genus. Resistance to copper allowed L. capsici AZ78 to be combined with a low-dose of a copper-based fungicide, leading to more effective control of grapevine downy mildew. Notably, prophylactic application of L. capsici AZ78 alone to grapevine leaves reduced downy mildew disease to the same degree as a copper-based fungicide. Furthermore, L. capsici AZ78 persists in the phyllosphere of grapevine plants and tolerates environmental stresses such as starvation, freezing, mild heat shock and UV light irradiation. These traits suggest that L. capsici AZ78 could be a suitable candidate for developing a new biofungicide to be used in combination with copper to control grapevine downy mildew.

Microsatellite Markers for Characterization of Native and Introduced Populations of Plasmopara viticola, the Causal Agent of Grapevine Downy Mildew

We reported 31 microsatellite markers that have been developed from microsatellite-enriched and direct shotgun pyrosequencing libraries of Plasmopara viticola, the causal agent of grapevine downy mildew. These markers were optimized for population genetics applications and used to characterize 96 P. viticola isolates from three European and three North American populations.