Pseudoperonospora Cubensis Research Articles

Temporal Dynamics of Two Genetically Diverse Downy Mildew Mitochondrial Clades on Cucumber Cultivars in South Carolina and Florida

Downy mildew (DM, Pseudoperonospora cubensis) is an important disease that can significantly reduce yield of field-grown cucumbers in the US. Cucumber cultivars with resistance to DM were widely grown for >30 years. However, resistance broke down in 2004 resulting in severe DM epidemics. Large plot trials were conducted to characterize pathogen virulence and population dynamics on DM tolerant cultivars Peacemaker and Expedition and susceptible SMR-58 in Charleston, SC and Fort Pierce, FL in 2016 and 2017. Rapid DM development on SMR-58 was observed at both locations in 2016 and 2017. Disease progress on Expedition and Peacemaker were slow as compared to SMR-58 in Fort Pierce, FL in 2016. Very low to no DM was observed on Peacemaker or Expedition in Charleston in 2016. In 2017, all cultivars were affected in Charleston, but only SMR-58 had severe DM (95-100%) in Fort Pierce. Pathogen population analysis using DM specific mitochondrial clade (MC1 and MC2) markers showed differences between the P. cubensis populations across location and years on the cucumber cultivars. Both MC1 and MC2 were detected in cucumber plots in SC and FL. The most prevalent DM mitochondrial clade in SC during June 2016 was MC1 primarily on SMR-58 (95-100%). However, in July 2016 that population shifted towards MC2 (45-77%). This suggested that the DM populations can change relatively quickly when suitable environment favors. Mixed populations of MC1 and MC2 continued to be observed in following year in Charleston, SC in 2017. In Fort Pierce, FL a complete shift was observed from MC2 in 2016 to MC1 in 2017. Since both MCs are present in the southeastern United States either at the same time or possibly different times during the production year, cultivars with combined resistance to P. cubensis populations will be needed to reduce reliance on fungicides to manage DM.

Biocontrol of plant pathogens by Lysobacter enzymogenes isolate LEC: efficacy of shake flask broth, fermentation broth and dried preparations

ABSTRACT The aim of our study was to upscale the production of Lysobacter enzymogenes strain LEC from shake flasks to a laboratory bioreactor. The obtained fermentation broth was to be downstream-processed by lyophilisation and fluidised bed-drying, followed by testing of the dried preparations against plant pathogens. Different batches of broth from shake flasks and from individual fermenter runs were characterised and compared. Number of viable cells, in vitro efficacy (ED90 value) against the apple scab pathogen Ventura inaequalis, as well as efficacy against Phytophthora infestans on potato plants were all reproducible and not impaired by upscaling the production volume from shake flask to the bioreactor. Fermentation broth was processed by lyophilisation and fluidised bed-drying. In bioassays, the activity against downy mildew (Pseudoperonospora cubensis) on cucumber were comparable for the unformulated fermentation broth and the fluidised bed-dried product, while the lyophilised product was significantly more effective. Strain LEC showed reproducible pathogen suppressive activity, independent from production scale and batch. Production upscaling and formulation by drying are possible without loss of efficacy.

Gene markers generating polygenic resistance in melon-Fusarium wilt-FOM1.2 interaction pathosystem.

Developing melon genotypes with resistance to Fusarium oxysporum f. sp. Melonis-(FOM) race1.2 is a major goal in any breeding program. In this study, we identified the role of 11 gene markers that contribute to polygenic resistance during the FOM1.2-melon interaction. qRT-PCR analysis elucidated upregulation of candidate marker genes AMT, DXPR, Fom-2, GLUC, GalS, GRF3, MLO, PRK, RuBlsCo, TLP and WRKY in resistant 'Shante-F1' and 'Khatouni', and susceptible 'Shante-T' and 'Shahabadi' at 7, 14 and 21 days post-inoculation (dpi). We also studied changes in defence-related enzyme activity: chitinase (CHI), β-1,3-glucanase (GLU) and peroxidase (POX) in melon roots. AMT, GLUC and DXPR transcripts were upregulatied in leaf and root tissues of the resistant 'Shante-F1' and 'Shahabadi'. Transcript levels for GalS and GRF3 increased 6.77- and 6.83-fold in roots of 'Shante-F1' at 7 dpi, whereas in PRK, TLP and WRKY theye increased by 7.84-, 5.15- and 12.26-fold at 14 dpi, respectively. However, transcript levels increased by 5.18-fold for Fom-2 and 8.46-fold for MLO at 21 dpi. Also, RBC transcript level peaked at 14 dpi with 4.9-fold increase in leaves of resistant genotypes, whereas AMT increased 2.94-fold at 21 dpi, and GLUC and DXPR increased 7.11- and 2.91-fold at 14 dpi in 'Shante-F', respectively. Defence-related-enzyme activity was also upregulated three-fold in resistant varieties. The dynamic shifts in the melon transcriptome induced by FOM1.2 emphasize that resistance mechanisms are predominantly regulated through signalling pathways involving CHI, GLU, and POX defence response. Surprisingly, the AMT gene, basically resistant to downy mildew, Pseudoperonospora cubensis; GLUC, MLO and PRK resistant to powdery mildew (Sphaerotheca fusca); TLP and WRKY resistant to Phytophthora blight (Phytophthora capsici); and GRF3 and RBC resistant to root knot nematodes (Meloidogyne spp.) were upregulated in resistant genotypes, indicating a dual role of these genes in resistance to more than one disease at a time.

Pseudoperonospora cubensis Causing Downy Mildew on Luffa aegyptiaca in Korea

In November 2021, sponge gourd (<i>Luffa aegyptiaca</i>) plants with typical downy mildew symptom were observed in Korea. Based on morphological characteristics of sporangiophores and sporangia, combined with molecular phylogenetic analysis of the internal transcribed spacer rDNA and <i>cox</i>2 mtDNA regions, the causal pathogen was identified as <i>Pseudoperonospora cubensis</i> (Oomycota). This is the first report of downy mildew caused by <i>P. cubensis</i> on <i>L. aegyptiaca</i> in Korea. Given that <i>P. cubensis</i> exhibits high disease incidence and severity on many Cucurbitaceae crops, it could pose a significant threat to sponge gourd cultivation.

Fungicidal Activity of Novel 6-Isothiazol-5-ylpyrimidin-4-amine-Containing Compounds Targeting Complex I Reduced Nicotinamide Adenine Dinucleotide Oxidoreductase.

To discover novel inhibitors of the complex I reduced nicotinamide adenine dinucleotide (NADH) oxidoreductase as fungicides, a series of 6-isothiazol-5-ylpyrimidin-4-amine-containing compounds were designed using a computer-aided pesticide design method and splicing of substructures from diflumetorim and isotianil. In vitro fungicidal bioassays indicated that compounds T17-T24 showed high inhibitory activity against Rhizoctonia solani with an effective concentration (EC50) value falling between 2.20 and 23.85 μg/mL, which were more active than or equivalent to the lead diflumetorim with its EC50 of 19.80 μg/mL. In vivo antifungal bioassays demonstrated that, at a concentration of 200 μg/mL, T7 and T21 showed higher inhibition against Pseudoperonospora cubensis than all other compounds, while T23 exhibited the highest inhibition against Sphaerotheca fuliginea. T23 showed an approximately twofold lower inhibition potency against R. solani complex I NADH oxidoreductase than diflumetorim. Molecular docking and transcriptomic analyses indicated that T23 and diflumetorim both might share the same mode of action, targeting NADH oxidoreductase. T23 as a good fungicidal candidate against R. solani is worthy of further investigation.

Synthesis and antifungal activity of novel piperidinyl thiazole derivatives.

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. 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. 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.

Identifying highly connected sites for risk-based surveillance and control of cucurbit downy mildew in the eastern United States.

Surveillance is critical for the rapid implementation of control measures for diseases caused by aerially dispersed plant pathogens, but such programs can be resource-intensive, especially for epidemics caused by long-distance dispersed pathogens. The current cucurbit downy mildew platform for monitoring, predicting and communicating the risk of disease spread in the United States is expensive to maintain. In this study, we focused on identifying sites critical for surveillance and treatment in an attempt to reduce disease monitoring costs and determine where control may be applied to mitigate the risk of disease spread. Static networks were constructed based on the distance between fields, while dynamic networks were constructed based on the distance between fields and wind speed and direction, using disease data collected from 2008 to 2016. Three strategies were used to identify highly connected field sites. First, the probability of pathogen transmission between nodes and the probability of node infection were modeled over a discrete weekly time step within an epidemic year. Second, nodes identified as important were selectively removed from networks and the probability of node infection was recalculated in each epidemic year. Third, the recurring patterns of node infection were analyzed across epidemic years. Static networks exhibited scale-free properties where the node degree followed a power-law distribution. Betweenness centrality was the most useful metric for identifying important nodes within the networks that were associated with disease transmission and prediction. Based on betweenness centrality, field sites in Maryland, North Carolina, Ohio, South Carolina and Virginia were the most central in the disease network across epidemic years. Removing field sites identified as important limited the predicted risk of disease spread based on the dynamic network model. Combining the dynamic network model and centrality metrics facilitated the identification of highly connected fields in the southeastern United States and the mid-Atlantic region. These highly connected sites may be used to inform surveillance and strategies for controlling cucurbit downy mildew in the eastern United States.

Screening of Bitter gourd (Momordica charantia L.) cultivars against Downy mildew caused by Pseudoperonospora cubensis under field conditions at Tarnab, Peshawar, Khyber Pakhtunkhwa, Pakistan

Screening of Bitter gourd (Momordica charantia L.) cultivars against Downy mildew caused by Pseudoperonospora cubensis under field conditions at Tarnab, Peshawar, Khyber Pakhtunkhwa, Pakistan

Early diagnosis of greenhouse cucumber downy mildew in seedling stage using chlorophyll fluorescence imaging technology

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.

Characteristics of fluopicolide-resistance mutants in Phytophthora nicotianae, the pathogen causing black shank disease in tobacco

Black shank, a devastating disease in tobacco production worldwide, is caused by the oomycete plant pathogen Phytophthora nicotianae. Fluopicolide is a pyridinylmethyl-benzamides fungicide with a unique mechanism of action and has been widely used for controlling a variety of oomycetes such as Plasmopara viticola, Phytophthora infestans, Pseudoperonospora cubensis, P. nicotianae and Bremia lactucae. However, the fluopicolide-resistance risk and molecular basis in P. nicotianae have not been reported. In this study, the sensitivity profile of 141 P. nicotianae strains to fluopicolide was determined, with a mean median effective concentration (EC50) value of 0.12 ± 0.06μg/mL. Five stable fluopicolide-resistant mutants of P. nicotianae were obtained by fungicide adaptation, and the compound fitness index of these resistant mutants were lower than that of their parental isolates. Additionally, cross-resistance tests indicated that the sensitivity of fluopicolide did not correlate with other oomycete fungicides, apart from fluopimomide. DNA sequencing revealed two point mutations, G765E and N769Y, in the PpVHA-a protein in the fluopicolide-resistant mutants. Transformation and expression of PpVHA-a genes carrying G765E and N769Y in the sensitive wild-type isolate confirmed that it was responsible for fluopicolide resistance. These results suggest that P. nicotianae has a low to medium resistance risk to fluopicolide in laboratory and that point mutations, G765E and N769Y, in PpVHA-a are associated with the observed fluopicolide resistance.

Deciphering the Enhancing Impact of Exogenous Brassinolide on Physiological Indices of Melon Plants under Downy Mildew-Induced Stress.

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.

Effect of Cucurbit Host, Production Region, and Season on the Population Structure of Pseudoperonospora cubensis in Florida.

Pseudoperonospora cubensis, the causal agent of Cucurbit downy mildew (CDM), is one of the most important diseases affecting cucurbit production in the United States. This disease is especially damaging to Florida production areas, as the state is a top producer of many cucurbit species. In addition, winter production in central and south Florida likely serves as a likely source of P. cubensis inoculum for spring and summer cucurbit production throughout the eastern United States, where CDM is unable to overwinter in the absence of a living host. Over 2 years (2017 and 2018) and four seasons (spring 2017, spring 2018, fall 2017, and fall 2018), 274 P. cubensis isolates were collected from cucurbit hosts at production sites in south, central, and north Florida. The isolates were analyzed with 10 simple sequence repeat (SSR) markers to establish population structure and genetic diversity and further assigned to a clade based on a qPCR assay. Results of population structure and genetic diversity analyses differentiated isolates based on cucurbit host and clade (1 or 2). Of the isolates assigned to clade by qPCR, butternut squash, watermelon, and zucchini were dominated by clade 1 isolates, whereas cucumber isolates were split 34 and 59% between clades 1 and 2, respectively. Clade assignments agreed with isolate clustering observed within discriminant analysis of principal components (DAPC) based on SSR markers, although watermelon isolates formed a group distinct from the other clade 1 isolates. For seasonal collections from cucumber at each location, isolates were typically skewed to one clade or the other and varied across locations and seasons within each year of the study. This variable population structure of cucumber isolates could have consequences for regional disease management. This is the first study to characterize P. cubensis populations in Florida and evaluate the effect of cucurbit host and clade-type on isolate diversity and population structure, with implications for CDM management in Florida and other United States cucurbit production areas.

New Insights into the Anti-Oomycete Mechanisms of a Leaf Extract from Glycyrrhiza glabra Against Pseudoperonospora cubensis.

Cucurbit downy mildew, caused by Pseudoperonospora cubensis, is responsible for high economic losses worldwide in cucumber production. Synthetic pesticides or copper-based products are still important tools to manage the disease. However, the pathogen has developed resistance against common fungicides rather quickly, and there is a need for alternative plant-protecting agents. Glycyrrhiza glabra leaf extract is known for its antifungal activity and was highly effective in former bioassays and semi-commercial trials against downy mildew of cucumber. To elucidate the active ingredients and the mode of action, licorice leaf extract was here fractionated into five fractions (F1 to F5) with a newly developed and optimized separation process via flash chromatography. The crude extract (P1) and fraction F1 inhibited the zoospore release from sporangia, the zoospore germination, and germ tube development of P. cubensis almost completely on two cucumber cultivars, one tolerant and one susceptible to the pathogen. Infestation rates were reduced between 73 and 96%. F1 contained three previously reported antifungal polyphenols: glabranin, pinocembrin, and licoflavanon. Here, we report an additional new compound, naringenin. Furthermore, F5 is found here to show some protective effects against P. cubensis, based on either direct fungicidal or indirect effects via the host plant. The presented results show that licorice leaf extract can serve as an alternative plant protection agent, able to manage P. cubensis infestation on cucumber cultivars with differing levels of susceptibility by interfering with important early stages in the pathogen development.

A Potential Fungicide against Pseudoperonospora Cubensis: Design, Synthesis and 3D-QSAR of New Pyrazole-5-Carboxamide Derivatives.

Downy mildew is one of the major fungi causing significant economic losses to crops. The resistance of this fungus to current fungicides is increasing and new fungicides with a unique mode of action are needed. To find a novel pyrazole amide derivative as a potential fungicide. A series of pyrazole-5-carboxamide derivatives containing a diaryl ether were designed and synthesized by the Intermediate derivatization method (IDM). Their fungicidal activities against Pseudoperonospora cubensis (P. cubensis, cucumber downy mildew) were evaluated in the greenhouse. Bioassays indicated that several compounds exhibited excellent fungicidal activity against P. cubensis in vivo. In particular, T24 (EC50 = 0.88 mg L-1) had the highest activity compared with Dimethomorph and Fluazinam and other analogues. The relationship between the activity and the structure of these derivatives was analyzed, and an accurate and reliable three-dimensional quantitative structure-activity relationship (3D-QSAR) model was established to determine that electrostatic and steric fields had important effects on the improvement of fungicidal activity. The novel pyrazole-5-carboxamide derivative T24 can be considered a potential fungicide for P. cubensis control.

Design, synthesis, antifungal activity and molecular docking of novel pyrazole-4-carboxamides containing tertiary alcohol and difluoromethyl moiety as potential succinate dehydrogenase inhibitors.

Resistance problems with the long-term and frequent use of existing fungicides, and the lack of structure diversity of traditional pyrazole-4-carboxamide succinate dehydrogenase inhibitors, it is highly required to design and develop new fungicides to address the resistance issue. Different from previous pyrazole-4-carboxamide succinate dehydrogenase inhibitors by breaking the norm of difluoromethyl at the C-3 position of pyrazole and introducing a tertiary alcohol group at the C-3 position, 27 novel pyrazole-4-carboxamide derivatives were designed, synthesized and characterized by proton (1 H) nuclear magnetic resonance (NMR), carbon-13 (13 C) NMR, fluorine-19 (19 F) NMR and high-resolution electrospray ionization mass spectrometry (HR-ESI-MS). The crystal structures of compounds A14 and C5 were analyzed by single crystal X-ray diffraction. Their in vitro antifungal activities were evaluated against phytopathogen Fusarium graminearum, Botrytis cinerea, Phytophthora capsica, Sclerotinia sclerotiorum, Thanatephorus cucumeris. The results displayed that most of them exhibited significant antifungal activities against S. sclerotiorum at 50 mg/L, the half maximal effective concentration (EC50 ) data of A8 and A14 were 3.96 and 2.52 mg/L, respectively. Their in vivo antifungal activities were evaluated against Pseudoperonospora cubensis, Puccinia sorghi Schw, Colletotrichum gloeosporioides, F. graminearum, Erysiphe graminis, Thanatephorus cucumeris, the control efficacies of A6, B3, C3, and C6 against E. graminis reached 100% at a concentration of 400 mg/L. The molecular docking results showed that the binding mode of the target compounds containing tertiary alcohols were similar to that of fluxapyroxad in succinate dehydrogenase. In addition, tertiary alcohols were involved in the formation of hydrogen bonds. The excellent in vitro and in vivo inhibitory activities of novel pyrazole-4-carboxamide derivatives against succinate dehydrogenase were reported for the first time, and they could be used as the potential lead compounds. © 2023 Society of Chemical Industry.

Scheduling Fungicide Applications for Cucurbit Downy Mildew Control on Pickling Cucumber in Michigan Using Disease Forecasters

Cucumber production is important to Michigan's economy and was valued at more than $45 million in 2019. Cucurbit downy mildew (CDM), caused by Pseudoperonospora cubensis, is an annual threat to Michigan's cucumber production, and fungicides must be applied frequently to prevent major yield losses. Our objective was to evaluate the disease forecasting models TOM-CAST, BLITE-CAST, and DM-CAST for their application in scheduling fungicide applications for CDM control. Field trials were conducted in 2021 and 2022 to evaluate each disease forecaster at different spray thresholds compared with 7- and 10-day programs and an untreated control. In 2021, all treatments received applications of cyazofamid alternated with oxathiapiprolin/chlorothalonil alternated with ametoctradin/dimethomorph plus chlorothalonil. The 2022 fungicide program was similar to that of 2021 except that cyazofamid was tank-mixed with chlorothalonil. Treatment plots were visually assessed for the foliar area (%) with CDM symptoms, and the relative area under the disease progress curve was determined at the end of each season. The results indicate that using DM-CAST or BLITE-CAST to schedule fungicide applications limited CDM and was similar to the 7-day program. The 7-day program received 7 (2021) and 6 (2022) applications, whereas DM-CAST and BLITE-CAST required 4 to 8 or 5 to 6 applications, respectively, depending on the threshold and year. This is the first study to evaluate these disease forecasters for scheduling fungicide application intervals for CDM.

Conventional and Biopesticide Fungicides for Cucurbit Downy Mildew Control on Cucumber in Michigan

Michigan ranks first in the nation in cucumber production for processing (pickling), contributing over $45 million to the state's economy in 2019. Cucurbit downy mildew, caused by the oomycete Pseudoperonospora cubensis, is the most important disease of cucumber and an annual threat to yields. Fungicides are the most important means to control P. cubensis. Our goal was to monitor currently labelled conventional fungicides and biopesticides for efficacy over the course of an entire cropping period under high pathogen pressure. Field trials were conducted at the Michigan State University Plant Pathology Research Farm in 2021 and 2022. Fungicides were applied weekly, and disease severity was evaluated by visually assessing the percentage of foliar area showing downy mildew symptoms. At the end of the season, the relative area under the disease progress curve (rAUDPC) was calculated using the disease severity data. Based on rAUDPC results, oxathiapiprolin premixed with chlorothalonil was the most effective fungicide at controlling P. cubensis and was significantly better than all other conventional fungicides in both years tested. In both years, all conventional treatments had a significantly lower rAUDPC than the untreated control except pyraclostrobin, dimethomorph, and fluopicolide. No biopesticide fungicide reduced the rAUDPC compared with the untreated control in either year evaluated.

Natural field diagnosis and molecular confirmation of fungal and bacterial watermelon pathogens in Bangladesh: A case study from the Natore and Sylhet districts.

The study investigated watermelon diseases characterized by contrasting climatic conditions in the Sylhet and Natore Districts of Bangladesh. Sylhet experiences lower temperatures and high rainfall, while Natore has higher temperatures and low rainfall. In these survey regions, 40 watermelon fields were selected, and 10 diseases were observed, including 4 fungal, 3 bacterial, 2 water mold, and 1 viral disease. The observed diseases were Anthracnose, Cercospora leaf spot, Fusarium wilt, Gummy stem blight, Downy mildew, Phytophthora fruit rot, Bacterial fruit blotch, Angular leaf spot, Yellow vine, and Watermelon mosaic disease. Molecular analysis was done in the Plant Pathology Lab at Sher-e-Bangla Agricultural University using the specific primers for fungal (ITS1/ITS4) and bacterial (27F/1492R) DNA regions and identified nine pathogen species, excluding the causal organism of the viral disease. The identified pathogens included Colletrotrichum orbiculare, Cercospora citrullina, Fusarium oxysporum, Stagonosporopsis cucurbitacearum, Pseudoperonospora cubensis, Phytophthora capsici, Acidovorax citrulli, Pseudomonas syringae, and Serratia marcescens. The sequencing of the identified pathogens revealed high homology (98.91-99.71%) with known sequences in the GenBank database. Phylogenetic analysis showed six clusters for fungal and water mold pathogen isolates and three for bacterial isolates where the percentages of replicate trees were 100% in all the cases. Among the identified diseases, the highest disease occurrence was caused by Fusarium wilt (47.5%) followed by Gummy stem blight (41.5%) in the Sylhet region and Angular leaf spot (37.5%) followed by Yellow vine (33%) in the Natore area. Fusarium wilt also has a high disease intensity, demonstrating its devastating impact on yield. This study highlights the influence of environmental conditions on disease incidence and underscores the need for tailored management strategies. These findings provide a foundation for developing targeted disease management practices for sustainable watermelon cultivation in Bangladesh.

Transcriptome-based analysis of candidate gene markers associated with resistance mechanism to Phytophthora melonis that causes root and crown rot in pumpkin.

Root and crown rot incited by an oomycete, Phytophthora melonis, causes significant yield losses in commercial pumpkin (Cucurbita pepo) production worldwide. Currently, resistant cultivars and knowledge of molecular mechanism of C. pepo against P. melonis are scarce. Here, we analysed the quantitative gene expression changes of 10 candidate gene markers (bHLH87, ERF014, HSF, MYB, PR-1, WRKY21, CPI, POD, PSK, SGT) in pumpkin roots and leaves at three time points (h post-inoculation, hpi) following inoculation with P. melonis in two resistant (Ghelyani and Tanbal), and two susceptible (Marmari and Khoreshti) varieties of pumpkin. Gene expression using quantitative real time PCR along a time course revealed the strongest transcriptomic response at 48 and 72hpi in resistant genotypes, 1.1-2.7-fold in roots and leaves, respectively, with a high significant correlation (r=0.857**-0.974**). We also found that CPI, PSK, SGT1 and POD act as a dual regulator that similarly modulate immunity not only against P. melonis, but also against other diseases such as early blight (Alternaria cucumerina), powdery mildew (Podosphaera xanthii), downy mildews (Pseudoperonospora cubensis), and pathogenic plant nematodes (Meloidogyne javanica). Furthermore, significantly higher activities of the ROS scavenging defence enzymes, catalase (1.6-fold increase) and peroxidase (6-fold increase) were observed in the roots of resistant cultivars at different hpi compared with non-inoculated controls. In addition, the biomass growth parameters including leaf and root length, stem and root diameter, root fresh weight and volume were significantly different among studied genotypes. Cumulatively, the transcriptome data provide novel insights into the response of pumpkins for improving pumpkin breeding to P. melonis.

Potential of compound bacterial agent in the biocontrol of muskmelon pathogens

The bacterial strain TG6 was screened from the soil of a muskmelon greenhouse, which could effectively inhibit the growth of Sphaerotheca fuliginea, Fusarium oxysporum, Phytophthora melonis and Pseudoperonospora cubensis of muskmelons. TG6 was identified as Bacillus subtilis through morphological, physiological, biochemical and molecular studies. Taking TG6 as the original strain, TG67 and TG69 were obtained by He-Ne laser mutagenesis. The microbial compound antagonist strain TG67 and TG69 was prepared in the ratio of 1:1 and applied to the biological control of greenhouse melon. Muskmelon field experiments showed that the bactericide could effectively control the occurrence of various diseases of muskmelon in greenhouse. Bangladesh J. Bot. 52(4): 1047-1053, 2023 (December)