Search Results (22)

Downy mildew, caused by the oomycete Pseudoperonospora cubensis, is the most destructive foliar disease of cucumbers. While partially resistant slicer cultivars (with spined fruits) are commercially available, no resistant Beit Alpha cultivars (characterized by smooth, dark green fruit) have been developed to date. Here, we report the successful breeding of downy mildew-resistant Beit Alpha cucumber lines. Resistance was transferred from the wild Sikkim cucumber accessions PI 197088 and PI 330628 (characterized by round fruit, with heavily netted brown rind). The resistance and fruit phenotype were restored through backcrosses to elite commercial susceptible cultivars. Due to the recessive nature of the resistance genes and their distribution across multiple chromosomes, the breeding program required multiple backcrosses and stringent selections for both resistance and fruit type. Full article

Downy mildew caused by the oomycete Pseudoperonospora cubensis is a devastating disease of cucurbits. Cucumis species are attacked by pathotype 3 (clade 2) of the pathogen, while Cucurbita species are attacked by pathotype 6 (clade 1). The Sikkim-type cucumbers PI 197088 and PI 330628 express high levels of resistance against both pathotypes (clades) of the pathogen but no green-fruit cucumber cultivars resistant to the disease are available on the market. Here we report on several non-Sikkim accessions of cucumber that show resistance against downy mildew in four consecutive seasons. Mean % foliage attacked with downy mildew in the susceptible controls Ilan and SMR-18 was 93% and 71%, respectively, as against 0.2% and 1.8% in the Sikkim-type resistant controls PI 197088 and PI 330628, respectively. Twenty-four green fruit accessions were significantly more resistant than the susceptible cucumber controls. Five accessions showed less than 10% infected leaf area with downy mildew as follows: PI 432870—5%, PI 390266—7.5%, PI 418964—8.5%, PI 390258—8.8%, and G12—10%. PI 390258 and PI 390266 were susceptible to race 1 of powdery mildew but resistant to race 2, whereas PI 418964 was resistant to both races. These accessions may be used in breeding programs to accelerate the production of green-fruit, disease-resistant cucumbers. Full article

Cucurbit downy mildew, caused by Pseudoperonospora cubensis, is a devastating disease in cucumbers that leads to significant yield losses in many cucurbit-growing regions worldwide. Developing resistant cucumber varieties is a sustainable approach to managing this disease, especially given the limitations of chemical control and the evolving nature of pathogens. This article reviews the genetic basis of downy mildew resistance in cucumbers, emphasizing key resistance (R) genes and quantitative trait loci (QTLs) that have been mapped. Recent advances in molecular breeding tools, including marker-assisted selection (MAS), genomic selection (GS), and CRISPR/Cas9 genome editing, have accelerated the development of resistant cultivars. This review also explores the role of transcriptomics, genomics, and other ‘omics’ technologies in unraveling the molecular mechanisms behind resistance and offers insights into the future of breeding strategies aimed at long-term disease management. Management strategies for cucurbit downy mildew are discussed, along with the potential impacts of climate change on the occurrence and severity of downy mildew, highlighting how changing environmental conditions may influence disease dynamics. Integrating these advanced genetic approaches with traditional breeding promises to accelerate the development of downy mildew-resistant cucumber varieties, contributing to the sustainability and resilience of cucumber production. Full article

This study focused on downy mildew in hop caused by the pathogen Pseudoperonospora humuli. A systematic literature review was conducted using bibliometric analysis to explore trends in publishing, prominent research themes, and where research is being conducted on hop downy mildew. The databases Scopus, Web of Science, and ScienceDirect were used to identify publications spanning from 1928 to 2023. The analysis yielded 54 publications, with the most cited studies primarily focusing on disease management and host resistance. Additionally, these studies explored the genetic and pathogenic relationship between P. cubensis and P. humuli. A word co-occurrence map revealed that the main themes addressed in the publications included “hop”, “disease”, “downy”, “humuli”, “mildew”, and “Pseudoperonospora”. Notably, there was a particular emphasis on subtopics such as disease management, the disease reaction of hop cultivars, and the influence of weather factors on hop downy mildew. Notably, there was limited knowledge about the disease in regions with tropical climates. This study provides valuable information that can support and guide future research endeavors concerning downy mildew in hop cultivation. Full article

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

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

The development of new fungicides is vital for safeguarding crops and ensuring sustainable agriculture. Building on our previous finding that 4-(3,4-dichloroisothiazole)-7-hydroxy coumarins can be used as fungicidal leads, 44 novel coumarin ester derivatives were designed and synthesized to evaluate whether esterification could enhance their fungicidal activity. In vitro fungicidal bioassays indicated that compound 2ai displayed good activity against Alternaria solani, Botrytis cinereal, Cercospora arachidicola, Physalospora piricola and Sclerotinia sclerotiorum, with an EC₅₀ value ranging from 2.90 to 5.56 μg/mL, comparable to the lead compound 1a, with its EC₅₀ value ranging from 1.92 to 9.37 μg/mL. In vivo bioassays demonstrated that compounds 1a, 2ar and 2bg showed comparable, excellent efficacy against Pseudoperonospora cubensis at a dose of 25 µg/mL. Our research shows that the esterification of 4-(3,4-dichloroisothiazole) 7-hydroxycoumarins results in a fungicidal activity equivalent to that of its lead compounds. Furthermore, our density functional theory (DFT) calculations and 3D-QSAR modeling provide a rational explanation of the structure–activity relationship and offer valuable insights to guide further molecular design. Full article

Compatibility interactions between the host and the fungal proteins are necessary to successfully establish a disease in plants by fungi or other diseases. Photochemical and antimicrobial substances are generally known to increase plant resilience, which is essential for eradicating fungus infections. Through homology modeling and in silico docking analysis, we assessed 50 phytochemicals from cucumber (Cucumis sativus), 15 antimicrobial compounds from botanical sources, and six compounds from chemical sources against two proteins of Pseudoperonospora cubensis linked to cucumber downy mildew. Alpha and beta sheets made up the 3D structures of the two protein models. According to Ramachandran plot analysis, the QNE 4 effector protein model was considered high quality because it had 86.8% of its residues in the preferred region. The results of the molecular docking analysis showed that the QNE4 and cytochrome oxidase subunit 1 proteins of P. cubensis showed good binding affinities with glucosyl flavones, terpenoids and flavonoids from phytochemicals, antimicrobial compounds from botanicals (garlic and clove), and chemically synthesized compounds, indicating the potential for antifungal activity. Full article

Although synthetic pesticides play a major role in plant protection, their application needs to be reduced because of their negative impact on the environment. This applies also to copper preparations, which are used in organic farming. For this reason, alternatives with less impact on the environment are urgently needed. In this context, we evaluated eight isolates of the genus Lysobacter (mainly Lysobacter enzymogenes) for their activity against plant pathogens. In vitro, the investigated Lysobacter isolates showed broad antagonistic activity against several phytopathogenic fungi, oomycetes and bacteria. Enzyme assays revealed diverse activities for the tested isolates. The most promising L. enzymogenes isolate (LEC) was used for further detailed analyses of its efficacy and effective working concentrations. The experiments included in vitro spore and sporangia germination tests and leaf disc assays as well as ad planta growth chamber trials against Alternaria solani and Phytophthora infestans on tomato plants, Pseudoperonospora cubensis on cucumbers and Venturia inaequalis on young potted apple trees. When applied on leaves, dilutions of a culture suspension of LEC had a concentration-dependent, protective effect against the tested pathogens. In all pathosystems tested, the effective concentrations were in the range of 2.5–5% and similarly efficacious to common plant protection agents containing copper hydroxide, wettable sulphur or fenhexamid. Thus, the isolate of L. enzymogenes identified in this study exhibits a broad activity against common plant pathogens and is therefore a promising candidate for the development of a microbial biocontrol agent. Full article

Based on the modification of natural products and the active substructure splicing method, a series of new N-(thiophen-2-yl) nicotinamide derivatives were designed and synthesized by splicing the nitrogen-containing heterocycle natural molecule nicotinic acid and the sulfur-containing heterocycle thiophene. The structures of the target compounds were identified through ¹H NMR, ¹³C NMR and HRMS spectra. The in vivo bioassay results of all the compounds against cucumber downy mildew (CDM, Pseudoperonospora cubensis (Berk.et Curt.) Rostov.) in a greenhouse indicated that compounds 4a (EC₅₀ = 4.69 mg/L) and 4f (EC₅₀ = 1.96 mg/L) exhibited excellent fungicidal activities which were higher than both diflumetorim (EC₅₀ = 21.44 mg/L) and flumorph (EC₅₀ = 7.55 mg/L). The bioassay results of the field trial against CDM demonstrated that the 10% EC formulation of compound 4f displayed excellent efficacies (70% and 79% control efficacies, respectively, each at 100 mg/L and 200 mg/L) which were superior to those of the two commercial fungicides flumorph (56% control efficacy at 200 mg/L) and mancozeb (76% control efficacy at 1000 mg/L). N-(thiophen-2-yl) nicotinamide derivatives are significant lead compounds that can be used for further structural optimization, and compound 4f is also a promising fungicide candidate against CDM that can be used for further development. Full article

The downy mildew disease of cucurbits is considered the most economically damaging disease of Cucurbitaceae worldwide. The causal agent, Pseudoperonospora cubensis (Berkeley & Curtis), may cause complete crop losses of cucurbits. Few commercial cucurbit cultivars are resistant to this disease. Commercially, P. cubensis is controlled primarily with synthetic fungicides that inhibit or eliminate the pathogen. Several biological agents have also been identified that provide some level of control. In our study, foliar applications of three strains of Trichoderma harzianum and two native strains of Bacillus subtilis were evaluated for the control of the disease on cucumber plants grown under commercial greenhouse conditions. The study was conducted using a completely randomized design with six individual treatments during two production cycles: fall 2015 and spring 2016. The response variables included disease incidence and severity, plant height, total yield, fruit quality, and weight. B. subtilis provided the best control over the incidence and severity of the disease in both production cycles. Interestingly, while T. harzianum was less effective at controlling the disease, it enhanced plant growth and productivity, and produced a higher number of better-quality fruits per plot. This increased yield with higher quality fruits may result in higher profit for the growers. Full article

Mediterranean greenhouses are usually covered by plastic materials (films); these films allow light to pass through them, modifying some of their characteristics. The properties of the plastic cover influence the development of greenhouse crops. In addition, it can influence the stresses that the plants endure and the development of fungal diseases in the crop. The aim of this study is to analyze the effect that an experimental film cover, with high transmittance and high light diffusivity, produces on the development of fungal diseases on a cucumber crop (Cucumis sativus L.). Two different film covers were compared: (i) commercial film (transmittance of 85%; diffusivity of 60%); and (ii) experimental film (transmittance of 90%; diffusivity of 55%). The study was carried out across two autumn–winter crop cycles in a multi-span greenhouse divided into two isolated sectors. Three fungal diseases caused the main damage to the cucumber crop: downy mildew (Pseudoperonospora cubensis), powdery mildew (Sphaerotheca fuliginia) and gummy stem blight (Didymella bryoniae). In the case of powdery mildew, a greater severity in the sector was observed with the commercial film in comparison with the sector with the experimental film, with significant statistical differences between the two sectors in both crop cycles. Downy mildew and gummy stem blight were fungal diseases with less presence than downy mildew, and a greater presence of these two fungal diseases in the sector with the commercial film was also observed in both crop cycles. Full article

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, H₂O_2, 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. Full article

Plant elicitors enhance plant defense against pathogen attacks by inducing systemic acquired resistance (SAR) with no or low direct fungicidal activity. Here we report the synthesis of a novel plant elicitor candidate LY5-24-2 [3,4-dichloro-N-(3-chloro-5-(trifluoromethyl)pyridin-2-yl)isothiazole-5-carboxamide] and evaluation of its SAR inducing activity. Bioassays indicated that LY5-24-2 did not show significant anti-fungal activity but provided long-lasting resistance in Arabidopsis thaliana (A. thaliana) through promoting the accumulation of lignin, cellulose and pectin by 60.1%, 82.4% and 305.6%, respectively, at a concentration of 100 µM. LY5-24-2 also facilitated the closure of leaf stomata and increased the intracellular free Ca²⁺ by 47.8%, induced reactive oxygen species (ROS) accumulation, and inhibited the activity of ascorbate peroxidase (APX, EC 1.11.1.11) and catalase (CAT, EC 1.11.1.6) by 38.9% and 34.0%, respectively, as compared with the control at a concentration of 100 µM. LY5-24-2 induced SAR in plants and was dependent on the NPR1-mediated SA pathway by up-regulating expression of 2273 genes in A. thaliana. Meanwhile, LY5-24-2 also improved cucumber (Cucumis sativus L.) defense against Pseudoperonospora cubensis (P. cubensis) through promoting ROS accumulation and inhibiting activity of APX and CAT by 30.7% and 23.1%, respectively. Its expression of SA signaling genes CsNPR1, CsPR4 and CsPR5 was enhanced by 10.8, 5.8 and 6.6 times, respectively. These results demonstrated that LY5-24-2 is a novel elicitor candidate for plant protection via inducing SAR. Full article

Cucumber downy mildew (CDM) is a destructive plant disease caused by the air-borne oomycete pathogen Pseudoperonospora cubensis. CDM causes severe yield reduction of cucumber and significant economic losses. Biocontrol is a promising method to control CDM with the advantage of being beneficial to sustainable agricultural development. However, until now, no reviews of biocontrol of CDM have been reported. The objective of this review is to more comprehensively understand the biocontrol of CDM. In this review, the biological characteristics of P. cubensis are introduced, and strategies for screening biocontrol agents to suppress CDM are recommended. Then the current biocontrol agents, including fungi such as Trichoderma and biocontrol bacteria such as Bacillus, which possess the ability to control CDM, and their control characteristics and ability against CDM are also summarized. The potential mechanisms by which these biocontrol agents prevent CDM are discussed. Finally, several suggestions for future research on the biocontrol of CDM are provided. Full article