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Cucumber downy mildew, caused by Pseudoperonospora cubensis , typically remains hidden from view during its initial infection stage. To address this issue, this study proposed an early diagnosis model for greenhouse cucumber downy mildew. This study was conducted under controlled conditions, utilising a large-scale mobile chlorophyll fluorescence imaging system to monitor the samples during their seedling stage on a daily basis from the first day of inoculation. A total of 98 sets of fluorescence parameter values and corresponding fluorescence images were collected. Machine learning methods, such as recursive feature elimination (RFE) and Least Absolute Shrinkage and Selection Operator (LASSO) regression with L1 regularisation, were used to screen the chlorophyll fluorescence parameter Ft_D3, whose corresponding the chlorophyll fluorescence images were used as inputs to the proposed model, following by employing a convolutional neural network (CNN) transfer learning method to the early detection task of cucumber downy mildew in fluorescence images. The study improved the topology structure of ResNet50, the network model with a learning rate of 0.001 and 16 cycles as the optimal feature extractor. The results indicated that the enhanced network displayed improved performance in early detection of cucumber downy mildew compared with other CNNs. Infected leaves were distinguished from healthy leaves in the early stages of infection, specifically 3 days before the appearance of symptoms. The accuracy of the model in the task of early diagnosis of downy mildew was 94.76%. This study presents an efficient approach for the photosynthetic characterisation and early identification of cucumber downy mildew. • Chl-FI showed potential for early diagnosis of downy mildew. • The improved-ResNet model attained 94.76% accuracy for early disease detection. • The data proportion was modified to mimic natural plant disease spread. • The Focal loss function was used to solve the category imbalance problem. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Relevance. Downy mildew (Pseudoperonospora cubensis) is a serious problem when growing cucumber both in open and protected ground. One of the most effective methods of combating Pseudoperonospora cubensis is the cultivation of genetically resistant hybrids. To create them, it is necessary to include genetic markers in breeding work that speed up and increase the accuracy of selection. The F311 genetic marker of the SGR gene provides resistance to the destruction of chlorophyll, which can significantly reduce the rate of development of downy mildew, as well as preserve the growth and development of plants.Material and methods. In 2021-2022, at the Crimean Breeding Center, parental lines of cucumbers were studied in spring rotation in open ground. A total of 39 samples were studied. Their resistance to downy mildew against a natural infectious background was assessed on a 5-point scale. Hybrids were chosen as standards: St resistance – Phoenix+, St susceptibility – F1 Tchaikovsky, which scored the maximum damage score during visual assessment, All studied material was tested for the presence of the SGR gene for resistance to chlorophyll destruction using PCR analysis using the F311 marker.Results. The operating efficiency of the F311 (SGR) marker under the conditions of this experiment was 87.2%. And the efficiency of using the F311 (SGR) marker for assessing resistance to Pseudoperonospora cubensis is 84.6%. Based on the results of the experiment, we can conclude that the use of the F311 (SGR) marker will significantly speed up the process of selection and creation of hybrids resistant to Pseudoperonospora cubensis with a complex of economically valuable traits.

Downy mildew of cucurbits is a disease caused by the Oomycete Pseudoperonospora cubensis. It can cause considerable losses in cucurbit crops. Phylogenetic studies point to the existence of cryptic species of Pseudoperonospora. The objective of this study was to determine, the phylogeny of Pseudoperonospora species affecting cucurbits in different regions of Brazil. For this, leaves with symptoms of downy mildew were collected in areas of cucurbits production in the states of Pernambuco, Minas Gerais, Ceará, and the Distrito Federal. For phylogenetic analyses, DNA extraction was performed, and PCR reactions were carried out using primers DC-6 and LR-0, Cox2-F and Cox2-RC4, OomCox1-levup and OomCox1-levlo, FM79-C1 and FMPHY-10b, for amplification of the internal transcribed spacer (ITS) region, the mitochondrial cytochrome c oxidase subunit II (cox2), the mitochondrial cytochrome c oxidase subunit I (cox1) and cox2-cox1 intergenic spacer respectively. The nucleotide sequences were analyzed, edited, and aligned to perform Bayesian Inference analysis. The results of the phylogenetic analyses presented in the cox2-cox1-cox2_1-ITS concatenated tree indicate that in Brazil, the downy mildew of cucurbits is caused by phylogenetically distinct lineages of P. cubensis. [ABSTRACT FROM AUTHOR]

Downy mildew caused by Pseudoperonospora cubensis is one of the major production constraints of ridge gourd cultivation causing severe yield loss. Host resistance is the most effective and sustainable means of controlling this disease. Ten varieties and thirteen advanced breeding lines of ridge gourd were screened under natural epiphytotics for two seasons and ten moderately resistant lines were identified based on per cent disease index (PDI). Among them, two lines IIHR-DMR-18-4-4 and IIHR-DMR-18-65-1 clearly showed lower disease severity with PDI of 23.46 and 24.03, respectively, while highly susceptible lines showed higher disease severity with 73 PDI. The area under disease progress curve (AUDPC) values of the moderately resistant lines IIHR-DMR-18-4-4 and IIHR-DMR-18-65-1 (1171.86 and 1190.86) were one third of those of the highly susceptible lines (3648.35). Similarly apparent infection rate (r) per week was lower in the moderately resistant lines (0.88) than in the susceptible lines (1.23), indicating slow disease progression (slow mildew) in these moderately resistant lines. Moderate resistance reaction was confirmed by the production of fewer sporangia/cm2 (1.08 × 104/cm2) and lower percentage of infected leaf area (8.6%, 8.4%) which was almost ten times less than that observed in highly susceptible lines such as Pusa Nasdar and Jaipur Long with high sporangia production (1.48 × 105/cm2,1.14 × 105/cm2) and leaf area damage (67.8%, 76.9%) respectively. The identified moderately resistant lines IIHR-DMR-18-4-4 and IIHR-DMR-18-65-1 showed slow mildew development and can be utilized in the breeding program to develop resistant cultivars of ridge gourd with desirable horticultural traits. [ABSTRACT FROM AUTHOR]

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.

The objective of this research was to evaluate the effect of the application of silicon (SiO2) on the control of downy mildew (Pseudoperonospora cubensis) in cucumber (Cucumis sativus) crops. The location of the research was carried out at the "La María" Experimental Farm belonging to the State Technical University of Quevedo (UTEQ), located on the Quevedo-El Empalme road at km 7 of the Province of Los Ríos for two years. The fertilizer that was applied was silicon oxide (SiO2 at 32%), in different doses applied at 8, 23 and 40 days after sowing. A completely randomized block design (DBCA) was used, with six treatments and three repetitions per treatment. The variables that were evaluated were the severity of the downy mildew disease in different treatments and leaves of different heights using a visual evaluation scale and image processing. Some variables of agronomic interest and a benefit/cost type economic analysis were evaluated. To validate the image processing, a linear correlation with a visual scale was used and the rest of the variables were subjected to analysis of variance (Tukey p<0.05) to determine statistical differences. The results obtained show a positive correlation (R2: 0.98) of the Leaf Doctor program with the visual evaluation. The severity of downy mildew did not present differences between the treatments, but the greatest impact was on the lower leaves. Silicon presented positive effects on the different agronomic variables, but only the yield, diameter, length, and average weight of the fruit were higher at doses of 150 ppm of silicon. However, the 125-ppm dose is more profitable as it has no statistical differences with the 150-ppm dose. [ABSTRACT FROM AUTHOR]

The leucine-rich repeat receptor-like kinases (LRR-RLKs) compose a large gene family in plant genomes and implement essential functions in diverse plant physiology progress, including defence against pathogens. However, a systematic analysis of LRR-RLKs has not been accomplished in the economically important cucumber. 189 LRR-RLK genes were identified in the cucumber genome and further divided into 22 subgroups based on the sequence similarities in this study. A total of 31 segmental duplication events and 15 tandem duplication events were present in the genome, indicating that the two duplications were the main driving forces for the expansion of the LRR-RLK family in the cucumber. The expression profile analysis revealed that most of the CsLRR-RLKs were upregulated during a downy mildew infection, and resistant cucumbers comprised more upregulated CsLRR-RLKs than the sensitive lines. Taken together, our results provided information on the LRR-RLK gene family in the cucumber and contributed valuable information for the further research of CsLRR-RLKs.

Downy mildew is one of the most important diseases of cucurbits in the world and Iran. The development of the disease was investigated in a commercial variety (Sakata® F1 Hybrid Saso), three hybrids and eight pure lines of cucumber, four pure squash lines, and one commercial cultivar of watermelon (Sakata® F1 Charleston Gray 243) in two consecutive years (2017 and 2018 spring and summer) at the experimental field of the University of Guilan, Iran to identify the sources of resistance. Plants were regularly inspected until the downy mildew symptoms appeared. The disease was measured using standard scale and Image J software at five stages in the plant growing season. Comparison of disease progress curves, final severity of the disease, and area under the disease progress curve (AUDPC) showed that cucumber B10 and A12 pure lines were the most susceptible and resistant in both years, respectively. None of the squash lines were infected in the first year, but in the second year, two lines showed the disease symptoms, and the severity of the disease in these lines was close to each other. The commercial cultivar of watermelon was not infected in both years.

Penyakit Downy mildew yang disebabkan jamur Pseudoperonospora cubensis, masih menjadi kendala utama produksi semangka di Indonesia. Pengendalian menggunakan fungisida sintetik masih menjadi pilihan utama para petani hingga saat ini. Penelitian ini dilakukan untuk menguji efektivitas fungisida majemuk bahan aktif Mankozeb 65% dan Benalaksil 8% secara in vitro dalam menekan daya hidup jamur P. cubensis pada daun semangka. Penelitian dilaksanakan di Laboratorium Penyakit Tumbuhan, Jurusan Hama dan Penyakit Tumbuhan, Fakultas Pertanian, Universitas Brawijaya. Penelitian menggunakan rancangan acak lengkap (RAL) dengan 5 perlakuan konsentrasi dan 3 fungisida yang berbeda yaitu mankozeb, benalaksil, dan campuran mankozeb+benalaksil dengan ulangan 4 kali. Variabel yang diamati adalah persentase sporangium jamur P. cubensis utuh dan rusak setelah aplikasi, Tingkat Hambatan Relatif (THR), dan sifat aktivitas fungisida majemuk yang ditentukan berdasarkan nilai Nisbah Ko-toksisitas (NK). Hasil pengamatan diketahui bahwa sporangium P. cubensis berbentuk oval dan berwarna abu-abu keunguan. Sporangium nampak menggerombol disekitar jaringan stomata. Pada penelitian ini, semua perlakuan fungisida dapat merusak sporangium P. cubensis. Presentase sporangium utuh paling rendah ditemukan pada perlakuan fungisida majemuk (mankozeb dan benalaksil) dengan dosis 0,6 g/l yaitu sebesar 15,19%. Nilai THR paling tinggi sebesar 58% ditemukan pada aplikasi fungisida majemuk (mankozeb dan benalaksil). Berdasarkan hasil perhitungan nilai NK, diketahui bahwa fungisida majemuk (mankozeb dan benalaksil) mempunyai sifat sinergistik (NK ≥ 1) yang mampu merusak sporangium P. cubensis yang utuh.

Pseudoperonospora cubensis (downy mildew) is highly virulent to various Cucurbitaceae crops, including cucumber (Cucumis sativus). We tested chlorine dioxide application in a plastic greenhouse for environmentfriendly control of downy mildew disease. Spraying diluted chlorine dioxide suppressed downy mildew disease with 41.2% control efficacy. Thermal fogging with chlorine dioxide had a high control efficacy of 80.9%, confirming that this approach is useful for environment-friendly downy mildew control. Using thermal fogging to control diseases that are greatly affected by humidity, such as downy mildew, may be more effective compared with conventional dilution spray control methods.

Image processing algorithms were employed in present study to determine the level of damage caused by mildew disease on cucumber plants. Fifty of infected plant images were randomly selected and processed with the image processing algorithm developed using image processing toolbox module of MATLAB. Then the results obtained from the image processing algorithm were compared with the assessments of experts. The image processing method predicted the disease levels with 1.90 RMSE and Theil's UII of 0.0312. Kolmogorov–Smirnov test was used to test the normality assumption of the data and test results revealed a normal distribution (p˃0.05). Determination coefficient (R2 = 0.995, p < 0.01) and Pearson's correlation coefficient (r = 0.997, p < 0.01) indicated significant positive relationship between image processing and expert assessments. The study results indicated that present image processing algorithm could successfully be used in place of expert assessment for diagnosis of mildew disease in cucumber plants. [ABSTRACT FROM AUTHOR]

Background: As an investigative program around the development of novel oomycetes fungicides, a systematic exploration of piperidinyl thiazole fungicides employing a bioisosteric replacement strategy was planned., Results: A series of novel piperidinyl thiazole analogues were designed, synthesised, and evaluated as fungicides in vitro and in vivo against three oomycete fungal pathogens: Phytophthora infestans (P. infestans), Plasmopara viticola (P. viticola), and Pseudoperonospora cubensis (P. cubensis). Variation at four different regions of piperidinyl thiazole fungicides like Oxathiapiprolin and Fluoxapiprolin was considered. All variations delivered excellent in vitro and in vivo activity against P. infestans at extremely low concentrations. O-linked heterocyles, bicyclic piperidines, and sulfoximine-substituted aryls demonstrated the most robust transfer of in vitro activity into the greenhouse, while pyridones, acylated sulfoximines, and sultams showed less consistent results concerning the transfer. Specific compounds were selected for deeper evaluation of oomycetes activity. Several of them with representatives of all the series showed an excellent in vivo activity against P. viticola and P. cubensis. Among the most active compounds, P14 and P25 were further profiled in advanced studies and were found to have a robust curative potential. P14, P15, and P25 provided excellent control of P. infestans (in potato), P. viticola (in grapes), and P. cubensis (in cucumber) in field trials at dose rates of 20 and 30 g per hectare., Conclusions: A bioisosteric replacement strategy was successfully employed to identify novel piperidine thiazole derivatives with robust and commercially interesting control of oomycetes diseases in the greenhouse and under field conditions. A systematic exploration of various modifications of the piperidine thiazole class and their structure activity relationships was described. © 2024 Society of Chemical Industry., (© 2024 Society of Chemical Industry.)

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]

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. [ABSTRACT FROM AUTHOR]

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

Streptomyces padanus PMS-702 strain produces a polyene macrolide antibiotic fungichromin and displays antagonistic activities against many phytopathogenic fungi. In the present study, experimental formulations were assessed to improve the production of fungichromin, the efficacy of PMS-702 on the suppression of sporangial germination, and the reduction of cucumber downy mildew caused by Pseudoperonospora cubensis. PMS-702 strain cultured in a soybean meal-glucose (SMG) medium led to low levels of fungichromin accumulation and sporangial germination suppression. Increasing medium compositions and adding plant oils (noticeably coconut oil) in SMG significantly increased fungichromin production from 68 to 1,999.6 μg/ml. Microscopic examination reveals that the resultant suspensions significantly reduced sporangial germination and caused cytoplasmic aggregation. Greenhouse trials reveal that the application of PMS-702 cultural suspensions reduced downy mildew severity considerably. The addition of Tween 80 into the synthetic medium while culturing PMS-702 further increased the suppressive efficacy of downy mildew severity, particularly when applied at 24 h before inoculation or co-applied with inoculum. Fungichromin at 50 μg/ml induced phytotoxicity showing minor necrosis surrounded with light yellowish halos on cucumber leaves. The concentration that leads to 90% inhibition (IC90) of sporangial germination was estimated to be around 10 μg/ml. The results provide a strong possibility of using the S. padanus PMS-702 strain as a biocontrol agent to control other plant pathogens.

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.

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.

Survey was conducted for bitter gourd disease incidence in the five districts of eastern Uttar Pradesh in 2018-19 and 2019-20. The five districts with two tahsil was selected from Jaunpur, Varanasi, Azamgarh, Sultanpur and Mirzapur. Two village were selected in each tahsil with former field and the data were recorded separately. Jaunpur was severely infected with the maximum average PDI (25.58%) followed by Mirzapur (24.16%), Sultanpur (22.49%)and the minimum average PDI (15.41%) was recorded in Azamgarh in the year 2018-19. Similarly, in the year 2019-20 Mirzapur was found to be most affected district with an average PDI of 24.74% followed by Jaunpur (23.41%), Varanasi (22.61%), Sultanpur (21.49%) and the minimum average PDI (20.91%) was recorded in Azamgarh in year 2019-20. Among the several districts the maximum average PDI in the year 2018-19 was found in Jaunpur (25.58%) and minimum average PDI was recorded in Azamgarh (15.41%). In year 2019-20 the maximum average PDI was found in Mirzapur (27.74%) and minimum average PDI (20.91%) was recorder in Azamgarh District. [ABSTRACT FROM AUTHOR]

Se evaluó el efecto de la aplicación foliar suplementaria de calcio, sobre la producción de melón Amarillo cv. Natal F-1, en Lepanto, Puntarenas. Los tratamientos evaluados fueron: JMX-Ca (4,22 kg CaO/ha), JMX-Ca (2,41 kg CaO/ha), Manvert-Ca (4,22 kg CaO/ha), y un testigo (agua). La cosecha inició a los 58 días después del trasplante (ddt) para todos los tratamientos. Los datos muestran una importante variabilidad entre los tratamientos en cuanto al número de frutos exportables por metro lineal (1,79 – 2,06), rendimiento exportable (13638 – 16126 kg/ha), producción exportable (1318 – 1556 cajas/ha), peso promedio del fruto (1364,3 – 1433,0 g), porcentaje de sólidos solubles totales (10,90 – 11,88 °Brix), firmeza de la pulpa del fruto (26,94 – 28,38 N), severidad máxima de mildiú velloso (Pseudoperonospora cubensis) a los 50 ddt (3,83 – 4,17; escala 1-5), e incidencia de colapso de la planta a los 58 ddt (0 – 1,85 %). Solamente se presentaron diferencias significativas entre tratamientos para el porcentaje de sólidos solubles totales; el tratamiento de JMX-Ca a 4,22 kg CaO/ha obtuvo un mayor valor para esta característica (11,88 °Brix) en comparación a JMX-Ca a 2,41 kg CaO/ha y a Manvert-Ca a 4,22 kg CaO/ha (entre 10,90 y 11,15 °Brix), pero no fue diferente del testigo (11,45 °Brix). Se concluye que, bajo las condiciones en que se desarrolló el ensayo, no se justifica económicamente la aplicación foliar suplementaria de calcio.

The occurrence of cucumber downy mildew in solar greenhouses directly affects the yield and quality of cucumber. Chemical control methods may cause excessive pesticide residues, endanger food quality and safety, pollute the ecological environment, etc. Therefore, it is very important to predict the disease before its occurrence. To provide farmers with better and effective guidance for the prevention and control work, minimize the loss of disease damage, this article took cucumber ‘Lyujingling No. 2′ as the experimental material and acquired greenhouse environmental factors data by wireless sensors, including Temp (Temperature), RH (Relative Humidity), ST (Soil Temperature) and SR (Solar Radiation). LSTM (Long Short-Term Memory) neural network structure was constructed based on Keras deep learning framework to develop a prediction model with time-series environmental factors. Combined with the occurrence of downy mildew from manual investigation and statistics, through debugging the parameters, this article developed an occurrence prediction model for cucumber downy mildew and compared it with KNN (K-Nearest Neighbors Classification) and ANN (Artificial Neural Network). In the prediction model, the forecasted results of the four environmental factors were consistent with the true value distributions, and R2 (R-Squared) were all above 0.95. Among them, the ST variable predicted the best results, e.g., R2 = 0.9982, RMSE (Root Mean Square Error) = 0.08 °C, and MAE (Mean Absolute Error) = 0.05 °C. In the disease occurrence prediction model, the training accuracy was 95.99%, the Loss value was 0.0159, the disease occurrence prediction Accuracy was 90%, Precision was 94%, Recall was 89%, F1-score was 91%, the AUC (Area Under Curve) value was 90.15%, and Kappa coefficient was 0.80. It also had obvious advantages over other different models. In summary, the model had a high classification accuracy and performance, and it can provide a reference for the occurrence prediction of cucumber downy mildew in actual production.

N -acyl-homoserine lactones (AHLs), a well-described group of quorum sensing molecules, may modulate plant defense responses and plant growth. However, there is limited knowledge regarding the defense responses of non-model crops to AHLs and the mechanism of action responsible for the modulation of defense responses against microbial pathogens. In the present study, long-chain N -3-oxo-tetradecanoyl- l -homoserine lactone (oxo-C14-HSL) was shown to have a distinct potential to prime cucumber for enhanced defense responses against the biotrophic oomycete pathogen Pseudoperonospora cubensis and the hemibiotrophic bacterium Pseudomonas syringae pv. lachrymans. We provide evidence that AHL-mediated enhanced defense against downy mildew disease is based on cell wall reinforcement by lignin and callose deposition, the activation of defense-related enzymes (peroxidase, β-1,3-glucanase, phenylalanine ammonia-lyase), and the accumulation of reactive oxygen species (hydrogen peroxide, superoxide) and phenolic compounds. Quantitative analysis of salicylic acid and jasmonic acid, and transcriptional analysis of several of genes associated with these phytohormones, revealed that defense priming with oxo-C14-HSL is commonly regulated by the salicylic acid signaling pathway. We also show that treatment with short- (N -hexanoyl- l -homoserine lactone) and medium-chain (N -3-oxo-decanoyl- l -homoserine lactone) AHLs promoted primary root elongation and modified root architecture, respectively, resulting in enhanced plant growth. [ABSTRACT FROM AUTHOR]

Cucumber downy mildew (causative agent – Pseudoperonospora cubensis Rostowz) is one of the most harmful diseases of cucumbers in Kazakhstan. High variability of the fungus leading to the emergence of new aggressive pathotypes and consequently to loss of resistance by some crop cultivars causes ever-growing harmfulness of P. cubensis. The goal of the research is to carry out immunological evaluation of cucumber varieties and hybrids from 18 countries to Kazakhstanean population of the fungus and to assess their resistance against the background of artificial inoculation as well as to find stable sources of crop resistance to the disease. Eighty cucumber cultivars from Kazakhstan, Uzbekistan, Tajikistan, Turkey, India, Serbia, Russia, Ukraine, USA, Moldova, Germany, Netherlands, Italy, France, Israel, China, Taiwan and South Korea were tested for their resistance to the downy mildew in the field. Synthetic population of the cucumber downy mildew agent was used for inoculation. The studies in 2015–2016 resulted in the detection of 29 (36.2 %) cucumber varieties and hybrids that demonstrated a high rate of field resistance to the pathogen. Nine (11.2 %) varieties and hybrids appeared to be resistant, three (3.8 %) were moderately resistant, three (3.8 %) were susceptible, and 36 (45.0 %) cultivars of different origin appeared to be highly susceptible. Resistant cultivars were rather frequent among materials from Kazakhstan and Netherlands. Adoption and cultivation of resistant cucumber varieties will allow reducing application of chemical protection means, producing ecologically safe farm produce and avoiding pollution of ecosystems.

Most cultivars of cucumber are susceptible to Pseudoperonospora cubensis, the causal agent of cucurbit downy mildew. This study aimed to evaluate the potential of two methods for the pre-symptomatic detection of downy mildew in cucumber. First, we observed the infection process of downy mildew using digital infrared thermography, as measured by the maximum temperature difference (MTD) and spot temperature of symptomatic areas. Under controlled conditions, visible symptoms were observed 5.36 ± 0.10 days after infection with P. cubensis, while thermal differences were detected 4.42 ± 0.16 days after infection. The MTD values of infected leaves were higher compared to those of non-infected leaves, but the MTD decreased sharply before the symptoms of downy mildew became visible. Significant differences in the spot temperatures of the symptomatic areas were apparent between the infected and healthy leaves from 4 days after infection. Second, we observed a changes in the Fourier transform infrared spectroscopy (FTIR) spectra of infected leaves and three characteristic wavenumbers—2977 cm−1, 1544 cm−1, and 1050 cm−1—were selected for the pre-symptomatic detection of cucumber downy mildew. According to the peak areas at these wavenumbers, pre-symptomatic and symptomatic samples could be classified correctly. These results clearly demonstrate that both thermal infrared imaging and FTIR spectra allow for the discrimination of healthy and infected leaves before there are visible symptoms. The pre-symptomatic data may be useful for scheduling timely fungicide applications for early detection and subsequent control of this destructive disease of cucumber. [ABSTRACT FROM AUTHOR]

The objective of this study was to examine the effect of different concentrations of nitrogen on downy mildew severity on cucumber plants. Nitrogen (100-600 mg L-1) was applied to plants grown in pots under greenhouse conditions through irrigation water. The cucumber leaves were inoculated with a zoospore suspension of Pseudoperonospora cubensis, the causal agent of powdery mildew. Disease symptoms in plants treated with 300 mg L-1 nitrogen were significantly lower and 24% severity reduction was recorded. A positive effect on the leaf area was also noticed in cucumber plants with the application of 300 mg L-1 nitrogen. The results indicated that a cubic regression curve can be fitted to the disease progress for downy mildew, regardless of N treatments. Furthermore, the N enrichment affected the NH4-N and NO3-N content in leaves and soil as well as P content in the leaves. The application of 100 mg L-1 N significantly reduced Mn content in leaves. Therefore, nitrogen supply in the form of ammonium nitrate fertilizer could be considered as an efficient method for the control of downy mildew of cucumber. [ABSTRACT FROM AUTHOR]

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This work aimed to evaluate the application effect of different dosages of nitrogen and potassium topdressing on mildew severity and on yield and fruit quality of melon. The three cultivars, Jangada, Gaucho Casca de Carvalho and Gaucho Redondo Cone Sul were evaluated in Cerrado (savannah) and floodplain areas. At 34 days after sowing (DAS) the topdressing treatments with different dosages of nitrogen and potassium were applied. The mildew severity estimation started at 56 DAS and was performed in five-days intervals until the harvesting of the fruits. The yield and physicochemical characteristics of the collected fruits were evaluated at harvest. There was no significative interaction among nitrogen and potassium topdressing, the cultivars and cultivated areas. However, there was significative differences when the factors were analyzed in separate. The cultivar Gaucho Redondo Cone Sul showed a significant linear increase in the area under the disease progress curve and higher productivity on cerrado compared to the remaining cultivars. The cultivar Gaucho Casca de Carvalho produced heavier and with higher °Brix fruits on cerrado. It is possible to conclude that the applied topdressings did not reduce the mildew severity in all tested cultivars, but they increased the yield in the floodplain area without modifying the physicochemical characteristics of the pulp on the evaluated melon fruits. [ABSTRACT FROM AUTHOR]

The novel fungicide oxathiapiprolin has potential for the control of downy mildew of cucumber, which is caused by Pseudoperonospora cubensis . In this study, an in vitro bioassay with detached leaves was used to determine the baseline sensitivity to oxathiapiprolin for 77 Ps . cubensis isolates from 11 provinces in China. The baseline sensitivity curve was continuous, and the average EC 50 value was 2.23 × 10 −4  μg ml −1 . In field trials, the control of downy mildew of cucumber was greater with oxathiapiprolin at 20 or 30 g a.i. ha −1 than with dimethomorph at 262.5 g a.i. ha −1 . Oxathiapiprolin was taken up by cucumber roots and transported upwards to stems and leaves. The full length of PscORP1 , the gene that encodes the target protein of oxathiapiprolin in Ps . cubensis , was sequenced for the first time. Our results suggested that oxathiapiprolin will be an excellent alternative fungicide for control of cucumber downy mildew. However, as Ps . cubensis is a high-risk pathogen, resistance development to oxathiapiprolin should be monitored and managed. [ABSTRACT FROM AUTHOR]

In the present study, the effect of potassium phosphite on Pseudoperonospora cubensis- inoculated cucumber plants was investigated. Different defense-related enzymes including laccase, polyphenoloxidase and glucanase as well as total protein and lignin contents were analyzed. Anatomical alterations in plant tissues were analyzed using a light microscope. Expression changes in major pathogenesis-related genes were studied at different time courses. The highest expression of glucanase was observed in pre-inoculated plants (97% higher than control) at 24 h with 97% increase compared to the control plants, while Chitinase transcripts were accumulated at a maximum level in potassium phosphite-treated plants 96 h after inoculation with 93% increase over control plants. Analysis of polygalacturonase inhibitor proteins gene expression revealed a transcription peak (96% increase over control plants) 48 h after inoculation. The potassium phosphite-treated plants exhibited an increase in β-1,3-glucanase (82%) enzymatic activity as well as total protein (53%), polyphenoloxidase (21%), laccase (11%) and lignin contents (15%) in comparison to the control. The results of the anatomical assay showed an increase in the vascular bundle diameter in potassium phosphite-treated plants (174 μm) and a decrease in pathogen-treated leaves (66 μm) compared with the control (100 μm). It can be suggested that potassium phosphite treatment induced higher expression of plant defense genes and increased laccase and polyphenoloxidase activities which in turn enhanced lignin deposition in plant tissues. The findings of the present study would be implemented for designing a controlling program to decrease the adverse effect of Pseudoperonospora cubensis on cucumber plants. [ABSTRACT FROM AUTHOR]

Y18501 is a new oxysterol-binding protein inhibitor (OSBPI) with a similar structure to oxathiapiprolin. Y18501 showed strong inhibitory activities against Phytophthora spp. and Pseudoperonospora cubensis , with EC 50 ranging from 0.0005 to 0.0046 μg/mL. It also had good control efficacy on cucumber downy mildew (CDM) in the green house and in the field, and could effectively inhibit different development stages of P. cubensis , especially for sporangiophore production, sporangial production, mycelium extension, and elongation of germ tube. In addition, Y18501 showed excellent protective and curative activities against P. cubensis. It also had acropetal systemic mobility in the cucumber leaves, and could be taken up and translocated to the upper leaves more effectively from the lower leaves than from the roots. Y18501 had poorer permeability in cucumber leaves compared to oxathiapiprolin. The simultaneous application of Y18501 and chlorothalonil could significantly promote the inhibition of P. cubensis. [Display omitted] • Y18501 showed strong inhibitory activity against plant pathogenic oomycetes. • Y18501 had good control efficacy on cucumber downy mildew (CDM). • Y18501 showed excellent protective and curative activities against P. cubensis. • Y18501 had acropetal systemic mobility and poorer permeability in cucumber leaves. • Combined use of Y18501 and chlorothalonil promoted the inhibition of P. cubensis. [ABSTRACT FROM AUTHOR]

Michigan growers have had to annually manage cucurbit downy mildew (CDM) using fungicides since host resistance was overcome in 2005. Fungicide efficacy can vary year-to-year and combining intermediate resistance (IR) pickling cucumber cultivars with fungicides may help improve CDM management. The study objectives were to compare Citadel and Peacemaker (IR) with susceptible cultivars Expedition and Vlaspik for their response to CDM when treated with three fungicide programs or not treated. Also, determining the efficacy of single product fungicides across three field seasons was of interest. Fungicides were applied weekly in 2016 and 2017 to IR and susceptible cultivars and included: (i) chlorothalonil, (ii) cyazofamid + chlorothalonil alternated with propamocarb + chlorothalonil alternated with amectoctradin/dimethomorph + chlorothalonil; and (iii) oxathiapiprolin/chlorothalonil alternated with propamocarb + chlorothalonil, alternated with cyazofamid + chlorothalonil. Protecting IR cultivars with fungicides increased their total marketable yield compared to the untreated. In Peacemaker, chlorothalonil alone was equally effective as the other fungicide treatments at improving yield. Single-product fungicides were applied on a 7-day schedule to field plots from 2018 to 2020. The efficacy of some of the most effective fungicides was influenced by year. Oxathiapiprolin + chlorothalonil had reduced efficacy during the year with the highest disease pressure. There were significant interactions between year and fungicide; propamocarb and ethaboxam did not always correlate with higher disease pressure. IR cultivars should be protected with fungicides. A better understanding of the relationship between yield response and disease severity in IR cultivars and continued monitoring of fungicide sensitivity will help optimize fungicide use. • Protecting intermediate resistant cultivars with fungicides increased their total marketable yield. • In Peacemaker, chlorothalonil alone was equally effective as the other fungicide treatments at improving yield. • Reduced efficacy for propamocarb and ethaboxam did not always correlate with higher disease pressure. [ABSTRACT FROM AUTHOR]

Downy mildew pathogens affect several economically important crops worldwide but, due to their obligate nature, few genetic resources are available for genomic and population analyses. Draft genomes for emergent downy mildew pathogens such as the oomycete Pseudoperonospora cubensis, causal agent of cucurbit downy mildew, have been published and can be used to perform comparative genomic analysis and develop tools such as microsatellites to characterize pathogen population structure. We used bioinformatics to identify 2,738 microsatellites in the P. cubensis predicted transcriptome and evaluate them for transferability to the hop downy mildew pathogen, Pseudoperonospora humuli, since no draft genome is available for this species. We also compared the microsatellite repertoire of P. cubensis to that of the model organism Hyaloperonospora arabidopsidis, which causes downy mildew in Arabidopsis. Although trends in frequency of motif-type were similar, the percentage of SSRs identified from P. cubensis transcripts differed significantly from H. arabidopsidis. The majority of a subset of microsatellites selected for laboratory validation (92%) produced a product in P. cubensis isolates, and 83 microsatellites demonstrated transferability to P. humuli. Eleven microsatellites were found to be polymorphic and consistently amplified in P. cubensis isolates. Analysis of Pseudoperonospora isolates from diverse hosts and locations revealed higher diversity in P. cubensis compared to P. humuli isolates. These microsatellites will be useful in efforts to better understand relationships within Pseudoperonospora species and P. cubensis on a population level.

Grazing preferences of collembolans Ceratophysella sp. 1 were noted. The collembolans feed on the sporangia of Pseudoperonospora cubensis growing on plants Cucumis sativus in greenhouses in Esfahan province in Iran. Sporangia of Pseudoperonospora cubensis were the preferred food of all fungal species noted in the alimental tract of the springtails. All digestive tracts of the springtails contained sporangia of P. cubensis.