Cucumber Downy Mildew Research Articles

Recognition of Greenhouse Cucumber Disease Based on Image Processing Technology

This paper mainly studies the disease of cucumber downy mildew, powdery mildew and anthracnose leaf image processing and recognition technologies. Application of median filtering method of filtering noise, leaf spot disease of cucumber leaf color range segmentation part extract color feature parameters of the lesion site, characteristic parameters of the shape; extraction texture parameters by using gray level co-occurrence matrix. Based on the shortest distance methods to identify diseases of images. The experimental result showed that the current method on disease recognition accuracy rates more than 96%.

Effects of Host Plant Resistance and Fungicides on Severity of Cucumber Downy Mildew

Cucurbit downy mildew caused by the oomycete Pseudoperonospora cubensis (Berk. And Curt) Rostov is a major disease of cucumber (Cucumis sativus L.) (Palti and Cohen, 1980) globally. Chemical control of downy mildew is necessary to achieve high yields in the absence of adequate host plant resistance. Most of the currently grown cultivars have some resistance to downy mildew. Before the resurgence of the disease in 2004, host plant resistance was sufficient to control the disease without fungicide use, and downy mildew was only a minor problem on cucumber. There are currently no cultivars that show resistance at a level equal to that observed before 2004. However, differences in resistance exist among cultivars, ranging from moderately resistant to highly susceptible. In this study, we evaluated the disease severity and yield of four cucumber cultivars that differed in disease resistance and were treated with fungicide programs representing a range of efficacy levels. The experiment was a split plot design with six replications and four years. Disease was evaluated as chlorosis, necrosis, and reduction in plant size on a 0 to 9 scale. Cultigen had a large effect in all four years. Fungicide has a smaller effect on resistance component traits and a larger effect on yield traits. The effects of cultivar resistance and fungicides appear to be additive until a threshold where maximum yield is reached. Highly resistant cultigens such as PI 197088 required only the least effective fungicides to achieve highest yields, whereas moderately resistant cultigens required a more effective fungicide to reach a similar level of yield. Susceptible cultigens did not achieve high yield even with the most effective fungicide treatments. It is likely that, even as highly resistant cultivars are released, growers will need to continue a minimal fungicide program to achieve maximum yield.

Sensitivity of Pseudoperonospora cubensis to dimethomorph, metalaxyl and fosetyl-aluminium in Shanxi of China

Cucumber downy mildew, caused by the fungal pathogen Pseudoperonospora cubensis, is a devastating disease in Shanxi Province, China. Fungicides dimethomorph, metalaxyl and fosetyl-aluminium have been used in the disease management. In this study, 143 isolates of P. cubensis were collected from different geographic locations of Shanxi, and examined for their corresponding sensitivities to these fungicides using the leaf disc bioassay method. The EC50 values of the isolates to dimethomorph, metalaxyl and fosetyl-aluminium ranged from 0.0006 to 5.85 μg/ml (mean = 1.01 μg/ml, SD = 1.27), 0.0869 to >500.00 μg/ml (mean = 85.97 μg/ml, SD = 95.61 for the range of 0.0869–458.10 μg/ml) and 0.0066–114.50 μg/ml (mean = 7.89 μg/ml, SD = 15.33), respectively. Over 80% isolates showed the EC50 values to dimethomorph <2.0 μg/ml. This study is the first to report high levels of resistance to metalaxyl in P. cubensis populations in Shanxi Province, and seven isolates were found to be extremely high resistant with EC50 values >500 μg/ml. The most P. cubensis isolates showed a normal distribution of EC50 range between 0 and 18 μg/ml to fosetyl-aluminium, and a few high resistant isolates were found. No cross-resistance was found between any fungicides used in this study. The concept of resistance index (RI) was used to determine the resistance level to each fungicide for sub-population of the pathogen in each district of Shanxi Province.

Efficacy of leaf extract fractions of Glycyrrhiza glabra L. against downy mildew of cucumber (Pseudoperonospora cubensis)

An ethanolic leaf extract of Glycyrrhiza glabra L. (licorice) was highly effective in former bioassays and semi-commercial trials in controlling cucumber downy mildew (efficacy up to 99.0 % in bioassays and 83.0 % in semi-commercial trials). In order to elucidate the active ingredients and the mode of action, licorice leaf extract was fractionated into six fractions of defined substance classes, of which the fraction containing acidic substances (F6) showed highest efficacy (97.6 %). The calculated EC50 values after a probit analysis of concentration series of crude extract and fraction F6 were concentrations of 1.0 % (crude extract) and 0.6 % (fraction F6). Interestingly, the slopes of the resulting graphs were significantly different, pointing to different modes of action for the two treatments. Three flavonoid compounds could be detected. The substances were glabranin, licoflavanon and pinocembrin. All three are known for their antimicrobial and antifungal capacity against plant and human pathogens. Besides these flavonoids, results, such as the different EC50 values, indicated that other compounds may be involved in the activity of fraction F6 against P. cubensis on cucumber.

Time Scales of Inoculum Production and the Dynamics of the Epidemic

Time Scales of Inoculum Production and the Dynamics of the Epidemic

Bioefficacy of Cymoxanil and Mancozeb against downy mildew of cucumber (Cucumis sativus) caused by Pseudoperonospora cubensis

Cymoxanil (8%)+Mancozeb (64%) 72WP , a combination product of systemic and contact fungicide, was evaluated against downy mildew disease of cucumber caused by Pseudoperonospora cubensis(Berk. and Curt.) (Rostov.). Cymoxanil 50 WP and Cymoxanil (8%)+Mancozeb (64 %) 72WP at all concentrations, were found significantly effective in reducing the disease and in increasing the yield as compared to untreated control in both the years. The results of the pooled data analysis indicated that Cymoxanil (8%)+Mancozeb (64 %) 72 WP @1080 g ai/ha was significant and recorded a PDI of 22.02 and an highest yield of 12.49 tonnes/ha as against a PDI of 33.59 and yield 9.97tonnes/ha in untreated control. Since the price of the combined product is more, the cost benefit ratio was found highest in their individual components. The highest cost: benefit ratio was recorded in Mancozeb 75 WP1500 g ai/ha (1:10.45), followed by Cymoxanil 50WP 120g ai/ha (1:9.66). Thus, among the evaluated fungicides, Mancozeb 75 WP 1500g ai/ha and Cymoxanil50 WP 120g ai/ha applied at weekly interval recorded the highest cost :benefit ratio of 1:10.45 and 1:9.66 respectively.

Study on the Methods of Detecting Cucumber Downy Mildew Using Hyperspectral Imaging Technology

Abstract Hyperspectral imaging technology, which can integrate the advantages of spectral detection and image detection, meets the need of detecting the cucumber diseases fast and nondestructively. In this paper, hyperspectral imaging technology is adopted to detect the cucumber downy mildew fast and nondestructively. Firstly, hyperspectral images of cucumber leaves infected downy mildew are acquired by the hyperspectral image acquisition system. And optimum wavelengths are collected by the principal component analysis to get the featured images. Then the image fusion technology is adopted to combine collected images with the featured images to form new images by pixel-level image fusion. Finally, the methods of the image enhancement, binarization, corrosion and dilatation treatments are carried out, so the cucumber downy mildew is detected. The result shows that the accuracy rate of the algorithm for detecting cucumber disease can reach nearly 90%. Studies have shown that hyperspectral imaging technology can be used to detect cucumber downy mildew.

Research on Cucumber Downy Mildew Images Classification Based on Fuzzy Pattern Recognition

Research on Cucumber Downy Mildew Images Classification Based on Fuzzy Pattern Recognition

A data-driven model simulating primary infection probabilities of cucumber downy mildew for use in early warning systems in solar greenhouses

Treatment during the primary infection phase is essential for controlling cucumber downy mildew in solar greenhouses. An early warning model applicable to this phase would represent a foundation for early warning systems for managing the disease and reducing pesticide usage. Based on the input parameters that were both readily available and appropriately limited in number, EWMPICDW (early warning model for primary infection of cucumber downy mildew in solar greenhouses) was developed based on monitoring data, early warning theory and plant disease epidemiology. The elaboration of this model included clarification of the meaning of warning, monitoring the warning indicators, forecasting the warning situation, tracing the warning sources and controlling the warning situation. The definition of warning included disease occurrence (yes or no) and probability. Because the leaf wetness duration (LWD) played an important role in disease warning systems for crops in solar greenhouses and was difficult to monitor, the leaf wetness sensor and RH threshold model were investigated and combined to form a practical estimation solution for LWD. Within the warning situation forecasting model system, the infection condition and incubation early warning submodels received the most attention. The infection condition early warning submodel was developed by using a threshold method based on the combination of LWD and mean temperature in LWD. The temperature was chosen as the warning indicator for incubation, and the incubation early warning submodel was defined using nonlinear regression methods. The warning sources traceability algorithm was developed in relation to expert knowledge and in terms of a mode of disaster mitigation that involved cutting the disaster chain from the headstream. The method for controlling the warning situation was based on good agricultural practices (GAP). The early warning model was implemented as a system and was evaluated using data for 4 years at two sites in Beijing, China. The warnings can be provided more than 2 d before symptoms appear. Using EWMPICDW, a positive early warning is associated with a change in the chance of disease occurrence from 0.68 to 0.96. Accordingly, the probability of disease occurrence calculated for the early warning model was 96%. These results demonstrate that the data-driven model will support the development of early warning systems for primary infection by cucumber downy mildew in solar greenhouses.

Design, synthesis and structure–activity relationship of novel coumarin derivatives

The lead coumarin derivative (E)-methyl 3-methoxy-2-[2-(4-methylcoumarin-7-yloxymethyl)phenyl]acrylate was discovered by using an intermediate derivatisation method. To discover new coumarin derivatives with improved activity, a series of substituted coumarins were synthesised and bioassayed. The compounds were identified by ¹H NMR, IR, MS and elemental analysis. Bioassays demonstrated that some of the title compounds exhibited excellent fungicidal activity against cucumber downy mildew at 25 mg L⁻¹. The relationship between structure and fungicidal activity is reported. The present work demonstrates that coumarin derivatives containing methoxyacrylate moieties can be used as possible lead compounds for developing novel fungicides.

A disease warning-source traceability model based on disaster chain-styled theory for solar greenhouse cucumber downy mildew

Warning-source traceability provides basis for disease early warning in solar greenhouse vegetables. Using disaster chain-styled theory and plant epidemiological theory, disease warning-source traceability problems and disaster mitigation modes by cutting the disaster chain were systematically analyzed. The disease warning-source traceability model was tested for cucumber downy mildew in solar greenhouse conditions. The model took into account the multi-warning-sources of disease early warning un-der solar greenhouse conditions and their effects on the interpretation ways of disease early warning. The instance of cucumber downy mildew under solar greenhouse conditions was tracked and analyzed using the disease warning-source traceability model. The study shows that overcast, rainy, snowy and foggy weather conditions are the warning-sources of cucumber downy mildew. The spatial and temporal variability of solar greenhouse environment was detected, and then warning-sources information was determined. The model could provide decision-making support for obviating downy mildew disease situations in solar greenhouse cucumber.

EVALUATION OF THE NANOSILVER COLLOIDAL SOLUTION IN COMPARISON WITH THE REGISTERED FUNGICIDE TO CONTROL GREENHOUSE CUCUMBER DOWNY MILDEW DISEASE IN THE NORTH OF IRAN

ISHS VI International Postharvest Symposium EVALUATION OF THE NANOSILVER COLLOIDAL SOLUTION IN COMPARISON WITH THE REGISTERED FUNGICIDE TO CONTROL GREENHOUSE CUCUMBER DOWNY MILDEW DISEASE IN THE NORTH OF IRAN

PRELIMINARY STUDIES ON CUCUMBER DOWNY MILDEW ISOLATES IN NORTHERN THAILAND

The downy mildew (Pseudoperonospora cubensis) caused significant damage to cucumber in Thailand. The systematic characterization of the pathogen has not yet been intensively studied in the country. The cucumber downy mildew collected from various locations in the northern region of Thailand were studied based on morphology, host specificity, and molecular phylogenetic analysis of the ITS sequences. The morphology of downy mildew isolates was similar to the Palti and Korea isolates. Three different pathotypes were identified. Analysis of the ITS sequences revealed no intraspecific variability in the candidate sequences.

Novel 2′-hydroxylfurylchalcones: synthesis and biological activity

Twelve novel 2′-hydroxylfurylchalcones have been synthesized by Claisen–Schmidt condensation with galactosylisomaltol, a reagent prepared from lactose. The procedures are environmentally benign and economical. All the compounds are identified by IR, 1H NMR and 13C NMR spectroscopy and by mass spectrometry. Preliminary bioassays indicate that all the title compounds show moderately high herbicidal activities against the height and/or the fresh weight of the seedlings of cucumber, rape, amaranth, wheat, sorghum and Chinese sprangletop at 7.5 g of active ingredient per hm 2. However, the compounds exhibit weak fungicidal activities against cucumber powdery mildew, and no activities against rice blast, cucumber grey mould and cucumber downy mildew. The structure–activity relationships are discussed. The present work demonstrates that 2′-hydroxylfurylchalcones could be used as potential lead compounds for further study of novel herbicides.

Polyethylene Mulch Modifies Greenhouse Microclimate and Reduces Infection of Phytophthora infestans in Tomato and Pseudoperonospora cubensis in Cucumber

The individual and joint effects of covering the soil with polyethylene mulch before planting and fungicides commonly used by organic growers on tomato late blight (caused by Phytophthora infestans) were studied in three experiments conducted from 2002 to 2005. Application of fungicides resulted in inconsistent and insufficient late blight suppression (control efficacy +/- standard error of 34.5 +/- 14.3%) but the polyethylene mulch resulted in consistent, effective, and highly significant suppression (control efficacy of 83.6 +/- 5.5%) of the disease. The combined effect of the two measures was additive. In a second set of three experiments carried out between 2004 and 2006, it was found that the type of polyethylene mulch used (bicolor aluminized, clear, or black) did not affect the efficacy of late blight suppression (control efficacy of 60.1 to 95.8%) and the differences in the effects among the different polyethylene mulches used were insignificant. Next, the ability of the mulch to suppress cucumber downy mildew (caused by Pseudoperonospora cubensis) was studied in four experiments carried out between 2006 and 2008. The mulch effectively suppressed cucumber downy mildew but the effect was less substantial (control efficacy of 34.9 +/- 4.8%) than that achieved for tomato late blight. The disease-suppressing effect of mulch appeared to come from a reduction in leaf wetness duration, because mulching led to reductions in both the frequency of nights when dew formed and the number of dew hours per night when it formed. Mulching also reduced relative humidity in the canopy, which may have reduced sporulation.

Design, Synthesis and Biological Activity of New Strobilurin Derivatives with a 1H-Pyrazol-5-oxy Side Chain

A series of new strobilurin derivatives with a substituted pyrazole side chain (5 and 6) were designed and synthesized. The new derivatives were synthesized from substituted phenones as starting material via esterification, cyclization and condensation reactions. All compounds were identified by 1H NMR and IR spectral and elemental analyses. Preliminary biological evaluation showed that some of the compounds had good fungicidal activity against cucumber downy mildew (CDM) and wheat powdery mildew (WPM) at 6.25 and 1.56 mg L(-1), respectively. Some of the compounds showed insecticidal activity against armyworm (AW), green peach aphid (GPA) and culex mosquitoes at 600 mg L(-1).

Distribution of Baseline Sensitivities to Natural Product Physcion Among Isolates of Sphaerotheca fuliginea and Pseudoperonospora cubensis.

The ethanol extract from rhubarb was commercialized in China (Veguard, Physcion, 5 g/liter AS) for control of cucumber powdery mildew (Sphaerotheca fuliginea) and cucumber downy mildew (Pseudoperonospora cubensis). To provide the basic data for the risk assessment of resistance to this product, physcion was selected to represent the active ingredients to establish baseline sensitivity of powdery mildew and downy mildew populations. For powdery mildew, 262 isolates of S. fuliginea from nine regions and, for downy mildew populations, 116 isolates of P. cubensis from six regions were collected in China during 2004 and 2005 and tested for sensitivity. In addition, the sensitivity of a powdery mildew isolate was monitored for 15 asexual generations under selection pressure with physcion. The results showed that there was no significant difference among regions in the frequency distribution of baseline sensitivity to this ingredient for either cucumber powdery mildew isolates or cucumber downy mildew isolates. Baseline sensitivity was distributed as a normal unimodal curve with a mean median (50%) effective concentration (EC50) of 0.304 μg/ml for powdery mildew population and mean EC50 of 0.501 μg/ml for downy mildew population. The variation of sensitivity to physcion was low because the range factor (maximum EC50/minimum EC50 of isolates within population) varied from 1.63 to 3.42 among powdery mildew populations and from 1.70 to 2.38 among downy mildew populations. The powdery mildew isolate XZ4 did not decrease sensitivity under the selection pressure of physcion at the dose of EC70 for 15 generations.

Effects of garlic (Allium sativum) juice containing allicin on Phytophthora infestans and downy mildew of cucumber caused by Pseudoperonospora cubensis

The volatile antimicrobial substance allicin (diallylthiosulphinate) is produced in garlic when the tissues are damaged and the substrate allicin (S-allyl-l-cysteine sulphoxide) mixes with the enzyme alliin-lyase (E.C.4.4.1.4). Allicin undergoes thiol-disulphide exchange reactions with free thiol groups in proteins and it is thought that this is the basis of its antimicrobial action. At 50 μg ml-1, allicin in garlic juice inhibited the germination of sporangia and cysts and subsequent germ tube growth by Phytophthora infestans both in vitro and in vivo on the leaf surface. Disease severity in P. infestans-infected tomato seedlings was also reduced by spraying leaves with garlic juice containing allicin over the range tested (55–110 μg ml−1) with an effectiveness ranging from approximately 45–100%. Similarly, in growth room experiments at concentrations from 50–1,000 μg ml−1, allicin in garlic juice reduced the severity of cucumber downy mildew caused by Pseudoperonospora cubensis by approximately 50–100%. These results suggest a potential for developing preparations from garlic for use in specialised aspects of organic farming, e.g. for reducing pathogen inoculum potential and perhaps for use under glass in horticulture.

RDNA-ITS sequence analysis of pathogens of cucumber downy mildew and cucumber powdery mildew

To determine the pathogens of cucumber downy mildew and cucumber powdery mildew by molecular marker, we amplified and sequenced the rDNA-ITS region of the pathogens of cucumber downy mildew and cucumber powdery mildew collected from the Shanghai region. The intra-/interspecific sequence difference was analyzed by rDNA-ITS sequence. The results show that the length of rDNA-ITS1 and rDNA-ITS2 of cucumber downy mildew’s pathogen was 141 bp and 406 bp, respectively, with GC contents of 41.13% in ITS1 and 46.8% (Minhang and Jinshan District, sm1 and sm2) or 46.55% (Pudong District, sm3) in ITS2. The rDNA-ITS sequence was intraspecific conservation. The interspecific difference was related with their kin relationship. The pathogen of cucumber downy mildew was identified as Pseudoperonospora cubensis by molecular marker. The length of rDNA-ITS1 and rDNA-ITS2 of cucumber powdery mildew’s pathogen was 136 bp and 89 bp, respectively, with GC contents being 59.56% and 66.29%, and rDNA-ITS sequence being highly conservative in this study that was the same as Sphaerotheca cucurbitae. But the sequence difference between the strains in the Shanghai region in this study with S. fuliginea was 4.5%, which was identified by morphology. It is suggested that the pathogen of cucumber powdery mildew should be further clarified and determined.

Effectiveness of Azoxystrobin in the Control of Erysiphe Cichoracearum and Pseudoperonospora Cubensis on Cucumber

Effectiveness of Azoxystrobin in the Control ofErysiphe CichoracearumandPseudoperonospora Cubensison CucumberThe bioefficacy of azoxystrobin (Amistar 25 SC) was tested against cucumber downy mildew and powdery mildew diseases. The two season trials of field studies revealed that the disease progression of cucumber downy mildew and powdery mildew was successfully arrested by azoxystrobin. Spraying of azoxystrobin at various doses (31.25, 62.50 and 125g a.s./ha) revealed that 125 g a.s./ha (500 ml/ha) was considered as the optimum dose for the control of these diseases of cucumber. The treatment also recorded the highest yield of 13.23 and 14.46 tonnes/ha in the first and second season, respectively. No phytotoxic effect of azoxystrobin was observed in the both field trials even at four times of the recommended dose 125 g a.s./ha. The persistence of azoxystrobin at 250 and 500 g a.s./ha was observed up to seven days after last spraying. However, the persistence of azoxystrobin at 31.25, 62.50 and 125 a.s./ha was observed up to three to five days after last spraying. The safe waiting period for the harvest of cucumber fruits was 1.53 days in the first field trial and 2.37 days in the second field trial, respectively at azoxystrobin 125 g a.s./ha. The residues of azoxystrobin were at below detectable level (BDL) in the harvested cucumber fruits.