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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]

Sulfur is an essential macronutrient for plant growth and development, and sulfate transporter (SULTR) plays key roles in sulfate (SO42-) uptake and transport in higher plants. In this study, 10 SULTR genes (CsaSULTR1;1～CsaSULTR4;1) were identified in cucumber. Phylogenetic analysis showed that SULTRs from cucumber and Arabidopsis could be divided into four groups (GROUP 1～4). Most CsaSULTR genes contained 9～12 introns, and closely related members shared similar gene structures. Promoter analysis revealed that CsaSULTR genes may be involved in responses to hormones and environmental stress. Expression profiling analysis by RNA-seq indicated that CsaSULTR genes have distinct expression patterns in different tissues, and some of them had significantly changed expression in response to downy mildew infection. Our results provide a better understanding for further functional analysis of CsSULTR genes in cucumber. [ABSTRACT FROM AUTHOR]

Downy mildew is a major disease that severely restricts the healthy and sustainable development of the global grape and wine industry, so there is significant interest in breeding high-quality disease-resistant varieties. In this study, hybridization was carried out between two disease-resistant and four high-quality varieties for eight hybrid combinations. The downy mildew resistance of 6 hybrid parents and 350 hybrid F1 progeny was determined by the leaf disc inoculation test, and the frequency distribution of the disease resistance grades was analyzed for the different populations. Agarose gel electrophoresis and disease resistance identification were used to screen SSR molecular markers of the tested hybrids for resistance to downy mildew. The results showed that minor disease-resistance genes in V. vinifera varieties were the main determinant of the variation in disease susceptibility among different varieties. V. vinifera resistance to downy mildew is inherited by a quantitative trait controlled by multiple genes. Intraspecific hybridization of V. vinifera can be applied to breed suitable intermediate materials or new types of disease resistance. The screening and verification of simple-sequence repeats (SSR) as molecular markers revealed that UDV-304, UDV-305, and UDV-737 could be used as standard markers for the identification of downy mildew resistance of hybrid progeny of Ecolly and Cabernet Sauvignon, UDV-305 could be used for the hybrid progeny of Meili and Cabernet Sauvignon, and VMC8g9 could be used for the hybrid progeny of Ecolly or Meili and Dunkelfelder. The disease-resistant progeny selected in this study can be used as intermediate materials for the breeding of new high-quality, disease-resistant varieties by intraspecific recurrent selection in V. vinifera. The screened standard markers can be utilized for rapid batch identification of hybrid progeny of different hybrid combinations to facilitate molecular marker-assisted breeding. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Food Safety & Quality is the property of Journal of Food Safety & Quality Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

204 genotypes of cauliflower were screened against downy mildew (DM) through challenge inoculation during 2019–20 and 2020–21 and 12 genotypes were identified as resistant (DS < 1). The disease reaction of the genotypes was recorded under natural infection conditions at curding and flowering stages. The DM score at the flowering stage showed a strong positive correlation with challenge inoculation (r2 = 0.614). The inheritance of downy mildew resistance was determined using 10 F2s populations developed from three susceptible(S) varieties (Pusa Himjyoti, Pusa Sharad, Pusa Meghna) and five resistant (R) genotypes (BR-2, 3–5–1-1, CCm, BR-207, BR-161). The F2 plants expressed segregation into R and S plants as per the expected Mendelian ratio of 3:1 (p = 0.3–0.7) and revealed the monogenic dominant nature of resistance. The segregation of 118 F2:3 progenies and 121 RILs from Pusa Himjyoti × BR-2 and two confirmatory F2s from S × S (Pusa Himjyoti × Pusa Sharad) and R × R (3–5–1-1 × CCm) also confirmed the single gene inheritance. Uniform segregation ratio in diverse resistance sources along with three different susceptible backgrounds established the single gene theory of DM resistance in Indian cauliflower germplasm. These new sources for downy mildew resistance having a simple Mendelian inheritance patterns can be directly used in resistance breeding. [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]

Downy mildew is, globally, one of the most significant diseases in viticulture. Control of this pathogen is achieved through fungicide application. However, due to restrictions (from upcoming regulations) and growing environmental conscientiousness, it is critical to continuously enhance forecasting models to reduce fungicide application. Infection potential has traditionally been based on a 50 h–degree calculation (temperature multiplied by leaf wetness duration) measured by weather stations; the main climatic parameters for forecast modelling are temperature, relative humidity, and leaf wetness. This study took these parameters measured by a weather station and compared them with the same parameters measured inside a grape canopy. The study showed that the temperature readings by the weather station compared to inside the canopy recorded differences during the day but not at night; the relative humidity showed significant differences during both daytime and night; leaf wetness showed the highest differences and was statistically significant during both daytime and night. In conclusion, the measurement differences between inside of the canopy and at the weather station have significant impacts on the precision of forecasting models. Thus, using data from inside of a canopy for the prediction should lead to even less fungicide applications. [ABSTRACT FROM AUTHOR]

Downy mildew (DM), caused by P. cubensis, is harmful to cucurbits including luffa, with increased shortcomings associated with its control through cultural practices, chemical fungicides, and resistant cultivars; there is a prompt need for an effective, eco-friendly, economical, and safe biocontrol approach. Current research is therefore dealt with the biocontrol of luffa DM1 through the endophytic fungi (EF) consortium. Results revealed that T. harzianum (ThM9) and T. virens (TvA1) showed pathogen-dependent inducible metabolic production of squalene and gliotoxins by higher gene expression induction of SQS1/ERG9 (squalene synthase) and GliP (non-ribosomal peptide synthetase). Gene expression of lytic enzymes of EF was also induced with subsequently higher enzyme activities upon confrontation with P. cubensis. EF-inoculated luffa seeds showed efficient germination with enhanced growth potential and vigor of seedlings. EF-inoculated plants showed an increased level of growth-promoting hormone GA with higher gene expression of GA2OX8. EF-pre-inoculated seedlings were resistant to DM and showed an increased GSH content and antioxidant enzyme activities (SOD, CAT, POD). The level of MDA, H2O2, REL, and disease severity was reduced by EF. ACC, JA, ABA, and SA were overproduced along with higher gene expression of LOX, ERF, NCED2, and PAL. Expression of defense-marker genes (PPO, CAT2, SOD, APX, PER5, LOX, NBS-LRR, PSY, CAS, Ubi, MLP43) was also modulated in EF-inoculated infected plants. Current research supported the use of EF inoculation to effectively escalate the systemic immunity against DM corresponding to the significant promotion of induced systemic resistance (ISR) and systemic acquired resistance (SAR) responses through initiating the defense mechanism by SA, ABA, ET, and JA biosynthesis and signaling pathways in luffa. [ABSTRACT FROM AUTHOR]

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

Downy mildew species in the genus Plasmopara are obligate biotrophic pathogens responsible for destructive diseases of economically important cultivated and ornamental plants. During September 2020 and 2021, a downy mildew was observed on porcelain berry (Ampelopsis grandulosa var. brevipedunculata) in different locations in MD, USA. A total of thirteen samples were collected from an equal number of diseased plants. Phylogenetic analyses of the cytochrome c oxidase subunit 2 (cox2) and large subunit ribosomal RNA (nc LSU rDNA) gene regions indicated that they constituted an unknown species here described as Plasmopara ampelopsidis sp. nov. Concurrently, a second species on wild Vitis species was also found, among historical downy mildew specimens used in previous studies, and it is here described as Plasmopara carveri. These newly described species are closely related to Plasmopara viticola and Plasmopara muralis. Although molecular phylogenetic analyses strongly support the segregation of these species, diagnostic morphological characters for each species were not observed. Therefore, a list of specific substitutions in the cox2 region as diagnostic characters is provided. It remains unclear if these new species represent a threat to the grapevine industry, but it seems advisable to closely monitor the presence of the two species. [ABSTRACT FROM AUTHOR]

Abstract Background Pearl millet remains prone to many diseases; among them downy mildew caused by Sclerospora graminicola (Sacc.) Schroet is economically more important. The use of endophytic bacteria for management of downy mildew of pearl millet as eco-friendly approach is increasing attention as sustainable alternative to pesticides. The objective of the present study was to isolate endophytic bacteria from roots of pearl millet cultivars and assess for biocontrol activity against Sclerospora graminicola. Results Thirty pearl millet root bacterial endophytes (PMRBEs) were isolated and screened in vitro for biocontrol activities such as: siderophore production, hydrogen cyanide (HCN) production and 1-amino cyclopropane-1-carboxylate (ACC) deaminase activity. Sixteen isolates possessed siderophore production potential, 3 isolates were found to be HCN producers, and 30% of the bacterial endophytes showed a good growth on ACC supplemented plates. On the basis of biocontrol activities, promising endophyte PMRBE6 was selected for seed treatment as well as a foliar spray to manage downy mildew of pearl millet in screen house experiment. The isolate PMRBE6 was found to be effective in managing downy mildew disease. Grain yield, test weight, plant height and average number of productive tillers were found to be maximum on inoculation of seeds of different pearl millet cultivars with PMRBE6, and the results were statistically significant as compared to control. Conclusions On the basis of biochemical characterization and partial 16S rRNA sequencing, the isolate PMRBE6 was identified as Bacillus subtilis strain PD4 (Accession no. MN400209). Pearl millet root bacterial endophyte (PMRBE6) exhibiting biocontrol activities could be exploited in friendly, sustainable organic agriculture.

Downy mildew is a serious disease in cucumber production worldwide, which is caused by Pseudoperonospora cubensis (Berk. & Curt.) Rostov. Underlying the mechanism of cucumber response to downy mildew infection is important for breeding improvement and production; however, the research remains largely elusive. A comparative proteomic approach was used to reveal the differential accumulation of the proteomes from leaves of cucumber (susceptible line and resistant line) that were inoculated with P. cubensis or not by two-dimensional electrophoresis and MALDI-TOF/TOF MS. A total of 76 protein spots were successfully identified with significant changes in abundance (> 2-fold, P < 0.05) in downy mildew infected or not leaves for the susceptible line and resistant line. By the functional annotation, these proteins were classified into 8 groups including photosynthesis (29%), energy and metabolism (29%), cell rescue and defense (17%), and protein biosynthesis, folding and degradation (13%), unclassified (7%), nucleotide metabolism (3%), signal transduction (1%) and cellular process (1%). Among the 17 differentially expressed proteins between the resistant and susceptible cucumber line, most of the protein spots were concentrated in cell rescue and defense (4) and energy and metabolism (4). Moreover, a schematic diagram containing majority of the metabolic pathways of cucumber leaves in response to downy mildew was proposed. This network revealed the positive effect of several functional components in cucumber seedlings' resistant to downy mildew such as accumulation of energy supply and resistance-related proteins, hastened protein metabolism and photorespiratory, inhibited photosynthesis, and triggered photosystem repair and programmed cell death. Taken together, these results have advanced a further understanding of the key metabolic pathways of cucumber resistance to downy mildew and pathogen control in the proteomic level.

Abstract Background Long non-coding RNAs (lncRNAs) are regulatory transcripts of length > 200 nt. Owing to the rapidly progressing RNA-sequencing technologies, lncRNAs are emerging as considerable nodes in the plant antifungal defense networks. Therefore, we investigated their role in Vitis vinifera (grapevine) in response to obligate biotrophic fungal phytopathogens, Erysiphe necator (powdery mildew, PM) and Plasmopara viticola (downy mildew, DM), which impose huge agro-economic burden on grape-growers worldwide. Results Using computational approach based on RNA-seq data, 71 PM- and 83 DM-responsive V. vinifera lncRNAs were identified and comprehensively examined for their putative functional roles in plant defense response. V. vinifera protein coding sequences (CDS) were also profiled based on expression levels, and 1037 PM-responsive and 670 DM-responsive CDS were identified. Next, co-expression analysis-based functional annotation revealed their association with gene ontology (GO) terms for ‘response to stress’, ‘response to biotic stimulus’, ‘immune system process’, etc. Further investigation based on analysis of domains, enzyme classification, pathways enrichment, transcription factors (TFs), interactions with microRNAs (miRNAs), and real-time quantitative PCR of lncRNAs and co-expressing CDS pairs suggested their involvement in modulation of basal and specific defense responses such as: Ca2+-dependent signaling, cell wall reinforcement, reactive oxygen species metabolism, pathogenesis related proteins accumulation, phytohormonal signal transduction, and secondary metabolism. Conclusions Overall, the identified lncRNAs provide insights into the underlying intricacy of grapevine transcriptional reprogramming/post-transcriptional regulation to delay or seize the living cell-dependent pathogen growth. Therefore, in addition to defense-responsive genes such as TFs, the identified lncRNAs can be further examined and leveraged to candidates for biotechnological improvement/breeding to enhance fungal stress resistance in this susceptible fruit crop of economic and nutritional importance.

Abstract Background Downy mildew, the most devastating disease of spinach (Spinacia oleracea L.), is caused by the oomycete Peronospora effusa [=P. farinosa f. sp. spinaciae]. The P. effusa shows race specificities to the resistant host and comprises 19 reported races and many novel isolates. Sixteen new P. effusa races were identified during the past three decades, and the new pathogen races are continually overcoming the genetic resistances used in commercial cultivars. A spinach breeding population derived from the cross between cultivars Whale and Lazio was inoculated with P. effusa race 16 in an environment-controlled facility; disease response was recorded and genotyped using genotyping by sequencing (GBS). The main objective of this study was to identify resistance-associated single nucleotide polymorphism (SNP) markers from the cultivar Whale against the P. effusa race 16. Results Association analysis conducted using GBS markers identified six significant SNPs (S3_658,306, S3_692697, S3_1050601, S3_1227787, S3_1227802, S3_1231197). The downy mildew resistance locus from cultivar Whale was mapped to a 0.57 Mb region on chromosome 3, including four disease resistance candidate genes (Spo12736, Spo12784, Spo12908, and Spo12821) within 2.69–11.28 Kb of the peak SNP. Conclusions Genomewide association analysis approach was used to map the P. effusa race 16 resistance loci and identify associated SNP markers and the candidate genes. The results from this study could be valuable in understanding the genetic basis of downy mildew resistance, and the SNP marker will be useful in spinach breeding to select resistant lines.

Relevance. F1 hybrids breeding programs of onion are based on the use of nuclear cytoplasmic male sterility (NCMS). Breeding and seed production based on NCMS suggest a development of a female sterile maternal line, a maintainer line and a paternal component. The development of an isogenic pair of sterile line – maintainer line is one of the most labor-, time-consuming and intellectually-intensive stages of a breeding program, the implementation of which becomes more complicated with an increase in the number of traits / genes for which selection is carried out.Methods and results. This paper presents a genetic scheme for the development of a Downy mildewresistant (pathogen P. destructor) maintainer line of onion using marker-assisted selection (MAS). F2 populations were obtained from the cross of the female maintainer inbred line, Bn1- (13) (genotype – cytN msms pdpd) and male inbred line resistant to Downy mildew, No. 136 (genotype – cytT MsMs PdPd). DNA marker DMR1 were used for Downy mildew resistance gene Pd, jnurf13 – for maintainer gene ms and marker system 5`cob: orfA501 – for N, S and T cytoplasms. It was shown that the MAS application allow to develop a stable Downy mildew resistant maintainer line cytN msms PdPd in two generations.

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]

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

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

Main conclusion: Grapevine aspartic proteases gene family is characterized and five VviAPs appear to be involved in grapevine defense against downy mildew. Grapevine (Vitis vinifera L.) is one of the most important crops worldwide. However, it is highly susceptible to the downy mildew disease caused by Plasmopara viticola (Berk. & Curt.) Berl. & De Toni. To minimize the use of fungicides used to control P. viticola, it is essential to gain a deeper comprehension on this pathosystem and proteases have gained particular interest in the past decade. Proteases were shown to actively participate in plant-pathogen interactions, not only in the processes that lead to plant cell death, stress responses and protein processing/degradation but also as components of the recognition and signalling pathways. The aim of this study was to identify and characterize the aspartic proteases (APs) involvement in grapevine defense against P. viticola. A genome-wide search and bioinformatics characterization of the V. vinifera AP gene family was conducted and a total of 81 APs proteins, coded by 65 genes, were found. VviAPs proteins can be divided into three categories, similar to those previously described for other plants. Twelve APs coding genes were selected, and expression analysis was conducted at several time-points after inoculation in both compatible and incompatible interactions. Five grapevine APs may be involved in grapevine tolerance against P. viticola. Our findings provide an overall understanding of the VviAPs gene family and establish better groundwork to further describe the roles of VviAPs in defense against P. viticola. [ABSTRACT FROM AUTHOR]

Copyright of Acta Agriculturae Zhejiangensis is the property of Acta Agriculturae Zhejiangensis Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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]

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

It was previously shown that spraying with CaCl2, MgCl2, KCl, and K2SO4 and high N and Mg concentrations in the irrigation water of potted cucumber plants reduced powdery mildew, while medium P and high K concentrations increased powdery mildew. In the present work, we tested the effect of irrigation with N, P, K, Ca, and Mg and spraying with salts on downy mildew (Pseudoperonospora cubensis) of cucumber (CDM). In potted plants, an increase in N concentration in the irrigation water resulted in a major increase in CDM severity, while an increase in K or Ca concentrations resulted in a gradual increase in CDM severity. An increase in P and Mg concentrations in the irrigation water resulted in a major CDM decrease. Spraying with Ca, Mg, and K salts with Cl and SO4 anions resulted in CDM suppression in most cases, and a negative correlation was obtained between the salt and anion molar concentrations and the CDM severity. Using NaCl sprays, both Na and Cl concentrations were negatively related to the CDM severity. MgCl2 (0.1 M Cl), K2SO4 (0.1 M SO4), MgCl2 + K2SO4, and monopotassium phosphate (MKP, 1%) sprayed under commercial-like (CL) conditions significantly reduced CDM by 36.6% to 62.6% in one disease cycle, while, in a second cycle, CDM was significantly reduced only by K2SO4 and MKP. In conclusion, fertigation with P and Mg, and salt spraying decreased CDM, while only spraying under CL resulted in CDM suppression. [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]

An experiment was designed to identify the resistance source for downy mildew disease in different cucumber genotypes and its crosses developed from the same genotypes in half diallel mating design (excluding reciprocal crosses). Fifteen parents and 105 crosses of cucumber along with a check (Swarna Agethi) were screened under the natural condition with manual inoculation (spore suspension). The disease rating was recorded a month after planting and at a weekly interval was observed for seven weeks until plant growth ended. Ratings were done on 0 to 9 scales. Genotypes JB/11-028-595504 and SKY/AC-270-613481 showed resistance with an average per cent disease index (PDI) of 10.42 and 14.75, respectively, compared to genotype JB/11-197-613470 (72.58 PDI) which is highly susceptible. Among the crosses, SKY/AC-316-613484 × JB/11-028-595504 and SKY/AC-251-613477 × SKY/AC-270- 613481 expressed resistance with an average PDI of 8.94 and 10.23, respectively, as compared to susceptible check swarna agethi (68.92 PDI). [ABSTRACT FROM AUTHOR]

Plasmopara viticola (Berk. and M.A. Curtis) Berl. and De Toni is an obligate pathogen that causes grape downy mildew. An experiment was conducted in a farmer’s field in Linganahalli village of Bengaluru rural district in 2019 and 2020 in order to validate different fungicides on downy mildew of grapes. Seven treatments with seven different fungicides were used in the current study. The spray with cymoxanil 8 per cent + mancozeb 64 per cent @ 2g/L had the lowest PDI (10.05% in 2019 and 9.75% in 2020) and AUDPC (94.21 in 2019 and 83.97 in 2020), followed by the spray with fluopicolide 4.44 per cent + fosetyl-Al 66.67 per cent WG @ 2g/L. In terms of per cent reduction over control, the cymoxanil 8 per cent + mancozeb 64 per cent @ 2g/L treatment reduced disease severity by 80.49 per cent in 2019 and 82.17 per cent in 2020. During both years, the yield attributes of the chemicals mentioned above had increased. [ABSTRACT FROM AUTHOR]

The genus Pseudoperonospora, an obligate biotrophic group of Oomycota, causes the most destructive foliar downy mildew disease on many economically important crops and wild plants. A previously unreported disease by Pseudoperonospora was found on oriental pickling melon (Cucumis melo var. conomon) in Korea, which is a minor crop cultivated in the temperate climate zone of East Asia, including China, Korea, and Japan. Based on molecular phylogenetic and morphological analyses, the causal agent was identified as Pseudoperonospora cubensis, and its pathogenicity has been proven. Importantly, two phylogenetic clades of P. cubensis, harboring probably two distinct species, were detected within the same plots, suggesting simultaneous coexistence of the two clades. This is the first report of P. cubensis causing downy mildew on oriental pickling melon in Korea, and the confirmation of presence of two phylogenetic clades of this pathogen in Korea. Given the high incidence of P. cubensis and high susceptibility of oriental pickling melon to this disease, phytosanitary measures, including rapid diagnosis and effective control management, are urgently required.

Abstract Background Quinoa (Chenopodium quinoa Willd.) is an ancient grain crop that is tolerant to abiotic stress and has favorable nutritional properties. Downy mildew is the main disease of quinoa and is caused by infections of the biotrophic oomycete Peronospora variabilis Gaüm. Since the disease causes major yield losses, identifying sources of downy mildew tolerance in genetic resources and understanding its genetic basis are important goals in quinoa breeding. Results We infected 132 South American genotypes, three Danish cultivars and the weedy relative C. album with a single isolate of P. variabilis under greenhouse conditions and observed a large variation in disease traits like severity of infection, which ranged from 5 to 83%. Linear mixed models revealed a significant effect of genotypes on disease traits with high heritabilities (0.72 to 0.81). Factors like altitude at site of origin or seed saponin content did not correlate with mildew tolerance, but stomatal width was weakly correlated with severity of infection. Despite the strong genotypic effects on mildew tolerance, genome-wide association mapping with 88 genotypes failed to identify significant marker-trait associations indicating a polygenic architecture of mildew tolerance. Conclusions The strong genetic effects on mildew tolerance allow to identify genetic resources, which are valuable sources of resistance in future quinoa breeding.

The French American hybrid grape cultivars Corot noir and Arandell (Vitis sp.), and Vidal blanc and Petit Manseng (Vitis vinifera), along with different spray programs, were evaluated for potential organic production in Virginia from 2013 to 2014. Results obtained in the study demonstrate that organic wine grape production in Virginia can be achieved by using select grape cultivars and spray programs. With the exception of Vidal blanc, disease severity and disease incidence were below the threshold for maintaining healthy vines in all organically managed grape cultivars. ‘Vidal blanc’ was not sufficiently resistant to downy mildew (Plasmopara viticola), precluding it from potential organic management in Virginia. The study also demonstrated significant disease resistance in Virginia of the cultivar Arandell, released by Cornell University (Ithaca, NY) in 2013. The results suggest that the organically registered fungicide Bacillus subtilis is effective in reducing the severity and incidence of black rot (Guignardia bidwellii) and phomopsis cane and leaf spot (Phomopsis viticola). The chemistry of organically managed berries harvested in 2014 met minimum requirements for wine production with soluble solids, titratable acidity, and pH ranging from 18.7% to 20.2%, 7.6 to 8.0 g·L−1, and 3.3 to 3.4, respectively, in ‘Arandell’ and ‘Corot noir’; and 21.0% to 24.4%, 7.8 to 9.6 g·L−1, and 2.7 to 2.9, respectively, in ‘Petit Manseng’ and ‘Vidal blanc’ juice.

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

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

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

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

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

Improving large-seeded waxy corn for food and industrial purposes is one way to increase the value and utilization of new corn cultivars in Thailand. This study aimed to evaluate the agronomic traits, yield and yield components, and response to downy mildew (DM) disease caused by Peronosclerospora sorghi of the developed breeding lines of large-seeded waxy corn. A total of 33 waxy corn breeding lines with different seed sizes, row numbers, and kernel colors were selected from 2015 to 2018. The yield experiment was conducted at the Khon Kaen University, Khon Kaen, Thailand in the 2019/20 dry season and the 2020 rainy season. The breeding lines were also screened for DM resistance through artificial inoculation with spore suspension at farmers’ fields in two locations, namely, Sok Muang and Nong Bua, in the 2020 rainy season. Genotype had a significant effect on yields, yield components, and agronomic traits. However, the interactions between genotype and season were not significant for 1000-kernel dry weight and the number of rows per ear. ‘DRP-4’, RLW-4’, ‘RLW-6’, ‘RLW-7’, and ‘RLW- 10’ showed the highest 1000-kernel dry weight and the optimal number of rows. Corn grown at Sok Muang Village had higher disease severity than that grown at Nong Bua Village due to the high rainfall, low temperature, and high humidity at the area. The resistant check cultivar ‘Nei9008’ exhibited moderate resistance to DM at both locations. Although the inbred lines were susceptible to DM disease, they appeared to be a good source of large seeds. Therefore, the backcross breeding method is still needed to obtain DM-resistant germplasm for the further development of waxy corn cultivars. [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]

Downy mildew (DM) is one of the most serious diseases in sunflower-growing regions worldwide, often significantly reducing sunflower yields. The causal agent of sunflower DM, the oomycete pathogen Plasmopara halstedii, is highly virulent and aggressive. Studying regional disease spread and virulence evolution in the DM pathogen population is important for the development of new sunflower inbred lines with resistance to the existing DM pathogen. The sunflower line 803–1, as one of nine international differential hosts, has been used in the identification of P. halstedii virulent pathotypes in sunflower since 2000. The DM resistance gene in 803–1 was temporally designated Pl5 + based on allelic analysis but has not been molecularly characterized. In the present study, bulked segregant analysis and genetic mapping confirmed the presence of the Pl gene within a large gene cluster on sunflower chromosome 13 in 803–1, as previously reported. Subsequent saturation mapping in the gene target region with single nucleotide polymorphism (SNP) markers placed this gene at an interval of 3.4 Mb in the XRQ reference genome assembly, a location different from that of Pl5. Therefore, the Pl gene in 803–1 was re-designated Pl36 because it is not allelic with Pl5. Four SNP markers co-segregated with Pl36, and SNP SFW05743 was 1.1 cM proximal to Pl36. The relationship of eight Pl genes in the cluster is discussed based on their origin, map position, and specificity of resistance/susceptibility to DM infection. [ABSTRACT FROM AUTHOR]

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Six varieties of field pea (Pisum sativum L.) were sown at two sowing rates over two years to assess the impact on disease occurrence in a Baltic climate. The varieties used were Bruno (Latvia), Capella (Sweden), Clara (Sweden), Kirke (Estonia), Onward (Greece), and Vitra (Latvia). The two sowing rates were 120 seeds per m2 and 144 seeds per m2. The increase in sowing rate by 20% did not influence field pea diseases. Variety influenced the incidence of disease in field pea. The varieties most damaged by pod spot (Ascochyta blight caused by Ascochyta spp.) were Vitra and Onward and least damaged were Bruno and Clara. The variety most damaged by downy mildew (caused by Peronospora viciae) was Vitra and least damaged was Bruno. The variety most damaged by white mould (or Sclerotinia rot caused by Sclerotinia sclerotiorum (Lib.) de Bary) was Onward. The varieties that had the most disease damage were Vitra and Onward, while least susceptible were Clara and Bruno. Therefore, Clara and Bruno are recommended for field pea production in a Baltic climate.

The family Peronosporaceae, an obligate biotrophic group of Oomycota, causes downy mildew disease on many cultivated and ornamental plants such as beet, cucumber, grape, onion, rose, spinach, and sunflower. To investigate the diversity of Peronosporaceae species in Korea, we performed morphological analysis for dried plant herbariums with downy mildew infections by two largest genera, Peronospora and Plasmopara. As a result, it was confirmed that there are five species of Peronospora and two species of Plasmopara, which have been so far unrecorded in Korea, as well as rarely known in the world; Pl. angustiterminalis (ex Xanthium strumarium), Pl. siegesbeckiae (ex Siegesbeckia glabrescens), P. chenopodii-ambrosioidis (ex Chenopodium ambrosioides), P. chenopodii-ficifolii (ex Chenopodium ficifolium), P. clinopodii (ex Clinopodium cf. vulgare), P. elsholtziae (ex Elsholtzia ciliata), and P. lathyrina (ex Lathyrus japonicus). In addition, their phylogenetic relationship was inferred by molecular sequence analysis of ITS, LSU rDNA, and cox2 mtDNA. By rediscovering the seven missing species and barcoding their DNA sequences, this study provides valuable insights into the diversity and evolutionary studies of downy mildew pathogens.

Abstract Powdery mildew and downy mildew are two devastating diseases on cucumber and other cucurbit crops caused by Podosphaera xanthii and Pseudoperonospora cubensis, respectively. Identification and detection of these pathogens from field and plant material could be significant for the selection of resistant varieties and formulation of disease management strategies. In the present study, a duplex qPCR assay developed for simultaneous detection and quantification of both pathogens from different samples. Two sets of species-specific primers developed for the detection of P. xanthii and P. cubensis pathogens by targeting the internal transcribed spacer (ITS) region of the rDNA gene cluster. The specificity of designed primers was also evaluated against the different microbial, plant, soil, and environmental samples. Initially, the individual assays for P. cubensis and P. xanthii were validated using their corresponding species-specific primers, which amplified the prominent and distinctive products of ~ 705 bp and ~ 290 bp size, respectively. SYBR green-based duplex real-time PCR assay was developed to detect and quantify both mildew pathogens from different field samples. The species-specific oligonucleotide primer sets showed high specificity with melt curve peaks at 85.83 °C and 88.05 °C, for P. xanthii and P. cubensis, respectively. The relative quantification and lowest detection limit of qPCR assays using tenfold diluted plasmid (Csp1 and Csd1) DNA were estimated (0.1 pg/µl) through a standard curve. In this study, the species-specific PCR and qPCR assays in both simplex and duplex formats have been validated successfully. These assays could be useful for efficient detection and quantification of mildew pathogens from the cucumber and other cucurbit crops.

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

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