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Severe epidemics of cucurbit downy mildew caused by Pseudoperonospora cubensis have been observed in recent years in major cucumber‐producing regions in Kazakhstan. However, information on the pathogenic variability of P. cubensis that could facilitate screening of candidate cucumber varieties and hybrids prior to deployment for commercial production is currently not available. A total of 112 isolates were collected from 2014 to 2016 during surveys in three major cucumber‐producing regions of Kazakhstan. Single lesion isolates were tested for their compatibility with a differential host set composed of 12 genotypes. Most isolates were compatible with Cucumis sativus and C. melo subsp. melo, while none were compatible with Citrullus lanatus. Isolates differed primarily by their virulence to C. pepo subsp. pepo and Benincasa hispida. Based on the patterns of compatibility with the differential host set, 29 pathotypes were identified. Of these, 18 were associated with a specific production region, six occurred in two regions and five were present in all three regions. The number of virulence factors (VF) ranged from 2 to 10, with 65% of the pathotypes having eight or more VFs. Indices of diversity showed that virulence was very diverse within the pathogen populations. Clustering of pathotypes based on similarity in virulence showed the existence of two main clusters. The high pathogenic variability observed in this study suggests that newly developed cucumber varieties and hybrids with resistance to cucurbit downy mildew need to be evaluated against a wide range of pathotypes prior to their deployment for commercial production in Kazakhstan. [ABSTRACT FROM AUTHOR]

The downy mildew pathogen, Pseudoperonospora humuli, forms oospores abundantly in diseased hop tissue. Diverse monosporangial isolates of P. humuli derived from samples collected in Japan, Germany and the USA readily formed oospores within hop leaves when inoculated singly, suggesting homothallism. Single zoospore isolates also readily formed oospores within hop leaves, further supporting the homothallic nature of this oomycete. The majority of oospores were deemed viable based on cytoplasm characteristics and plasmolysis assays. However, disease symptoms failed to develop when hop leaves were inoculated with newly formed oospores, even when oospore conditioning was attempted with treatment with potassium permanganate or β-glucuronidase/arylsulphatase, brief exposure to freezing temperature, or passage through an earthworm. Oospores derived from a monosporangial isolate of P. humuli that overwintered outdoors in infested leaves buried in soil also failed to cause downy mildew. Pseudoperonospora humuli is homothallic and oospores of the organism appear to require as yet unknown conditions to stimulate their germination and/or infection. [ABSTRACT FROM AUTHOR]

Pseudoperonospora cubensis, the causal agent of cucurbit downy mildew ( CDM), is known to exhibit host specialization. The virulence of different isolates of the pathogen can be classified into pathotypes based on their compatibility with a differential set composed of specific cucurbit host types. However, the genetic basis of host specialization within P. cubensis is not yet known. Total genomic DNA extracted from nine isolates of P. cubensis collected from 2008 to 2013 from diverse cucurbit host types ( Cucumis sativus, C. melo var. reticulatus, Cucurbita maxima, C. moschata, C. pepo, and Citrullus lanatus) in the United States were subjected to whole-genome sequencing. Comparative analysis of these nine genomes confirmed the presence of two distinct evolutionary lineages (lineages I and II) of P. cubensis. Many fixed polymorphisms separated lineage I comprising isolates from Cucurbita pepo, C. moschata, and Citrullus lanatus from lineage II comprising isolates from Cucumis spp. and Cucurbita maxima. Phenotypic characterization showed that lineage II isolates were of the A1 mating type and belonged to pathotypes 1 and 3 that were not known to be present in the United States prior to the resurgence of CDM in 2004. The association of lineage II isolates with the new pathotypes and a lack of genetic diversity among these isolates suggest that lineage II of P. cubensis is associated with the resurgence of CDM on cucumber in the United States. [ABSTRACT FROM AUTHOR]

The F-box protein FBXW7 is the substrate-recruiting subunit of an SCF ubiquitin ligase and a major tumor-suppressor protein that is altered in several human malignancies. Loss of function of FBXW7 results in the stabilization of numerous proteins that orchestrate cell proliferation and survival. Little is known about proteins that directly regulate the function of this protein. In the current work, we have mapped the interactome of the enigmatic pseudophosphatase STYX. We reasoned that a catalytically inactive phosphatase might have adopted novel mechanisms of action. The STYX interactome contained several F-box proteins, including FBXW7. We show that STYX binds to the F-box domain of FBXW7 and disables its recruitment into the SCF complex. Therefore, STYX acts as a direct inhibitor of FBXW7, affecting the cellular levels of its substrates. Furthermore, we find that levels of STYX and FBXW7 are anti-correlated in breast cancer patients, which affects disease prognosis. We propose the STYX- FBXW7 interaction as a promising drug target for future investigations. [ABSTRACT FROM AUTHOR]

Pseudoperonospora cubensis is an oomycete pathogen causing downy mildew disease on a variety of Cucurbitaceae, and has recently re-emerged as a destructive disease on crops in this family, mainly on cucumber and squash. Multilocus sequence analysis ( MLSA) of four mitochondrial and two nuclear DNA regions was used to detect changes in the genetic structure of P. cubensis populations occurring in the Czech Republic that might be associated with recently reported shifts in virulence. The analysed sample set contains 67 P. cubensis isolates collected from 1995 to 2012 in the Czech Republic and some other European countries. Sequence analyses revealed differences and changes in the genetic backgrounds of P. cubensis isolates. While all isolates sampled before 2009 exhibited the genotype of the subspecies of Clade II and were collected from cucumber, all samples collected from other hosts belonged to Clade I ( P. cubensis sensu stricto) or were sampled from 2009 onwards. In addition, 67·16% of all post-2009 isolates from Clade II had two heterozygous positions in their nr ITS sequence, which suggests sexual reproduction and/or a mutational origin. Thus, the results indicate that, apart from the rise in prevalence of Clade I, the change in the genetic structure of P. cubensis populations may be linked with a hybridization or, less likely, a mutation event that rendered strains able to infect a broader spectrum of host species. [ABSTRACT FROM AUTHOR]

Fundamental to the development of models to predict the spread of cucurbit downy mildew is the ability to determine the escape of Pseudoperonospora cubensis sporangia from infected fields. Aerial concentrations of sporangia, C (sporangia m−3), were monitored using Rotorod samplers deployed at 0·5 to 3·0 m above a naturally infected cucumber canopy in two sites in central and eastern North Carolina in 2011, where disease severity ranged from 1 to 40%. Standing crop of sporangia was assessed each morning at 07·00 h EDT and ranged from 320 to 16 170 sporangia m−2. Disease severity and height above the canopy significantly ( P < 0·0001) affected C with mean concentration ( Cm) being high at moderate disease. Values of Cm decreased rapidly with canopy height and at a height of 2·0 m, Cm was only 7% of values measured at 0·5 m when disease was moderate. Daily total flux ( FD) was dependent on disease severity and ranged from 5·9 to 2242·3 sporangia m−2. The fraction of available sporangia that escaped the canopy increased from 0·028 to 0·171 as average wind speed above the canopy for periods of high C increased from 1·7 to 3·6 m s−1. Variations of Cm and FD with increasing disease were well described ( P < 0·0001) by a log-normal model with 15% as the threshold above which Cm and FD decreased as disease severity increased. These results indicate that disease severity should be used to adjust sporangia escape in spore transport simulation models that are used to predict the risk of spread of cucurbit downy mildew. [ABSTRACT FROM AUTHOR]

Downy mildew ( DM), caused by Pseudoperonospora cubensis (Berk. & M.A. Curtis) Rostovzev, is a worldwide major disease of cucumbers ( Cucumis sativus L.). By screening 10 introgression lines ( ILs) derived from interspecific hybridization between cucumber and the wild Cucumis, C. hystrix, through a whole plant assay, one introgression line ( IL52) was identified with high DM-resistance. IL52 was further used as a resistant parent to make an F2 population with 'changchunmici' (susceptible parent). The F2 population (300 plants) was investigated for DM-yellowing, DM-necrosis and DM-resistance in the adult stage. A genetic map spanning 642.5 cM with 104 markers was constructed and used for QTL analysis from the population. Three QTL regions were identified on chromosome 5 and chromosome 6. By interval mapping analysis, two QTLs for DM-resistance were determined on chromosome 5 (DM_5.1 and DM_5.2), which explained 17.9% and 14.2% of the variation, respectively. QTLs for DM-yellowing were in the same regions as DM-resistance. For DM-necrosis, by interval mapping analysis, one QTL was determined on chromosome 5 (Necr_5.1) that explained 18.3% of the variation and one on chromosome 6 (Necr_6.1) that explained 13.9% of the variation. Our results indicated that the identification of molecular markers linked to the QTLs could be further applied for marker-assisted selection ( MAS) of downy mildew resistance in cucumber. [ABSTRACT FROM AUTHOR]

The structure and temporal dynamics of the virulence of Pseudoperonospora cubensis (causal agent of cucurbit downy mildew) were studied in pathogen populations in the Czech Republic from 2001 to 2010. A total of 398 P. cubensis isolates collected from Cucumis ( Cm.) sativus, Cm. melo, Cucurbita ( Cr.) maxima, Cr. pepo, Cr. moschata and Citrullus lanatus were analysed for variation in virulence (pathotypes). Virulence was evaluated on a differential set of 12 genotypes of cucurbitaceous plants. All isolates of P. cubensis were characterized by their level of virulence (classified according the number of virulence factors, VF; low VF = 1-4, medium VF = 5-8, high VF = 9-12): high (75%), medium (24%) and low (1%). The structure and dynamics of virulence in the pathogen populations were expressed by pathotypes using tetrad numerical codes and a total of 67 different pathotypes of P. cubensis were determined. The most susceptible group of differentials was Cucumis spp., while the lowest frequency of virulence was recorded on Cr. pepo ssp. pepo, Ci. lanatus and Luffa cylindrica. A high proportion ( c. 90%) of isolates was able to infect cucurbit species Benincasa hispida and Lagenaria siceraria, which are not commonly cultivated in the Czech Republic or elsewhere in central Europe. In the recent pathogen populations (2008-2010) there was prevailing frequency (70-100%) of isolates with high numbers (9-12) of virulence factors. 'Super pathotype' 15.15.15 was often observed in the study within the pathogen populations and was one of the four most frequently recorded pathotypes. Pseudoperonospora cubensis populations shifted to a higher virulence over time. From 2009 the pathogen population changed dramatically and new pathotypes appeared able to establish natural and serious infection of Cucurbita spp. and Ci. lanatus, which was not observed in 2001-2008. Generally, virulence structure and dynamics of P. cubensis populations are extremely variable in the Czech Republic. [ABSTRACT FROM AUTHOR]

Oospore formation of Pseudoperonospora cubensis was investigated in 10 Chinese locations: Mohe, Harbin, Changchun, Shenyang, Beijing, Liaocheng, Yinchuan, Xining, Yangling and Haikou. Oospores were observed in all but Haikou. Oospore viability was monitored from 10 January to 10 July 2009, in Harbin. Percentages of activated oospores increased from 10 April with a peak in late May (14.0% on 25 May 2009), and then decreased. This is in accordance with the usual time of downy mildew appearance in Harbin, 20-30 May. Inoculation tests using the oospores overwintered in Harbin, whether in the greenhouse or outdoors, showed that these were viable, with a disease occurrence of 26.6-95.0%. Oospores overwintering locally could be primary infection sources of downy mildew in cool temperate northern China. [ABSTRACT FROM AUTHOR]

Downy mildew, a foliar disease caused by the oomycete Pseudoperonospora cubensis (Berk. and Curt.) Rostov. is one of the most destructive diseases of cucumber (Cucumis sativus L.). Moderately resistant cultivars are available, but yield losses are high without the use of fungicides. Higher levels of resistance are needed to reduce the need for fungicides. The objective of this study was to identify new sources of resistance to downy mildew among Plant Introduction accessions from the U.S. National Plant Germplasm System, elite cultivars, and breeding lines of cucumber. A total of 1300 cultigens were tested in Clinton, NC, and Skierniewice, Poland, in 2005 to 2007 under natural field epidemics. The most resistant and susceptible cultigens were further evaluated in replicated experiments in North Carolina and India in 2007 to 2009. Fungicide experiments were run in 2008 and 2009 to identify tolerance, involving weekly applications to one of two sets of material at a location. Results from the retest study confirmed the results of the initial screening. The most resistant cultigens over all environments were PI 605996, PI 330628, and PI 197088. Cultigens have been found that significantly outperform checks in all resistance traits. High yielding and tolerant cultigens have also been identified that could be used in developing improved cultivars. [ABSTRACT FROM AUTHOR]

BACKGROUND: Pseudoperonospora cubensis, the causal oomycete agent of cucurbit downy mildew, is responsible for enormous crop losses in many species of Cucurbitaceae, particularly in cucumber and melon. Disease control is mainly achieved by combinations of host resistance and fungicide applications. However, since 2004, resistance to downy mildew in cucumber has been overcome by the pathogen, thus driving farmers to rely only on fungicide spray applications, including carboxylic acid amide (CAA) fungicides. Recently, CAA-resistant isolates of P. cubensis were recovered, but the underlying mechanism of resistance was not revealed. The purpose of the present study was to identify the molecular mechanism controlling resistance to CAAs in P. cubensis. RESULTS: The four CesA (cellulose synthase) genes responsible for cellulose biosynthesis in P. cubensis were characterised. Resistant strains showed a mutation in the CesA3 gene, at position 1105, leading to an amino acid exchange from glycine to valine or tryptophan. Cross-resistance tests with different CAAs indicated that these mutations lead to resistance against all tested CAAs. CONCLUSION: Point mutations in the CesA3 gene of P. cubensis lead to CAA resistance. Accurate monitoring of these mutations among P. cubensis populations may improve/facilitate adequate recommendation/deployment of fungicides in the field. Copyright © 2011 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Cucurbit downy mildew, caused by Pseudoperonospora cubensis, is a major cucumber disease in the Czech Republic. Disease prevalence, host range and disease severity were evaluated from 2001 to 2009. The geographical distribution of P. cubensis was assessed on ca 80-100 locations per year in two main regions of the Czech Republic (central and southern Moravia, and eastern, northern and central Bohemia). Infection by P. cubensis was observed primarily on cucumber ( Cucumis sativus) but only on the leaves. During the study, disease prevalence ranged from 66 to 100%. The majority of C. sativus crops were heavily infected at the end of the growing season (second half of August). Generally, P. cubensis was present at high or very high disease severity. The loss of foliage results in the reduction in the quality and quantity of marketable yield of fruit. Pseudoperonospora cubensis was widespread across the whole area of the Czech Republic studied. Very rarely, infection was recorded in muskmelon ( Cucumis melo) and Cucurbita moschata. Of other pathogens, the most frequently recorded was the cucurbit powdery mildew ( Golovinomyces cichoracearum and Podosphaera xanthii). [ABSTRACT FROM AUTHOR]

BACKGROUND: Pyrimorph is a novel fungicide being developed in China that shows high antifungal activity against diseases caused by Phytophthora infestans, Phytophthora capsici, Rhizoctonia solani, Peronophythora litchi and Pseudoperonospora cubensis. Until now, no information on the toxicity of pyrimorph to untargeted organisms has been reported. To assess the potential environmental impacts of pyrimorph in fish, the acute toxicity and bioconcentration of pyrimorph in zebrafish were studied in this paper. RESULTS: When tested by the semi-static method, the 48, 72 and 96 h median lethal concentration (LC50) values of pyrimorph to zebrafish were 24.33, 22.61 and 19.79 mg L−1 respectively. To study the bioconcentration of pyrimorph in zebrafish, the fish were exposed to sublethal concentrations of pyrimorph (2.00 and 0.25 mg L−1) for 192 h, a modified QuEChERS (Quick, Easy, Cheap, Effective, Rugged and Safe) method was applied to extract pyrimorph from samples and the residues of pyrimorph in the water and fish were determined by high-performance liquid chromatography (HPLC). The highest bioconcentration factor (BCF) of pyrimorph in the fish was 1.07 × 102 (144 h) and 23.1 (96 h) after exposure to 2.00 and 0.25 mg L−1 of pyrimorph respectively. CONCLUSIONS: The novel fungicide pyrimorph has low toxicity to zebrafish; however, it showed medium BCF to zebrafish. Therefore, more attention should be paid to the residue of pyrimorph in fish, as well as to its long-term ecological effects. Copyright © 2011 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Pseudoperonospora cubensis[(Berkeley & M. A. Curtis) Rostovzev], the causal agent of cucurbit downy mildew, is responsible for devastating losses worldwide of cucumber, cantaloupe, pumpkin, watermelon and squash. Although downy mildew has been a major issue in Europe since the mid-1980s, in the USA, downy mildew on cucumber has been successfully controlled for many years through host resistance. However, since the 2004 growing season, host resistance has been effective no longer and, as a result, the control of downy mildew on cucurbits now requires an intensive fungicide programme. Chemical control is not always feasible because of the high costs associated with fungicides and their application. Moreover, the presence of pathogen populations resistant to commonly used fungicides limits the long-term viability of chemical control. This review summarizes the current knowledge of taxonomy, disease development, virulence, pathogenicity and control of Ps. cubensis. In addition, topics for future research that aim to develop both short- and long-term control measures of cucurbit downy mildew are discussed. Kingdom Straminipila; Phylum Oomycota; Class Oomycetes; Order Peronosporales; Family Peronosporaceae; Genus Pseudoperonospora; Species Pseudoperonospora cubensis. Angular chlorotic lesions bound by leaf veins on the foliage of cucumber. Symptoms vary on different cucurbit species and varieties, specifically in terms of lesion development, shape and size. Infection of cucurbits by Ps. cubensis impacts fruit yield and overall plant health. Sporulation on the underside of leaves results in the production of sporangia that are dispersed by wind. On arrival on a susceptible host, sporangia germinate in free water on the leaf surface, producing biflagellate zoospores that swim to and encyst on stomata, where they form germ tubes. An appressorium is produced and forms a penetration hypha, which enters the leaf tissue through the stomata. Hyphae grow through the mesophyll and establish haustoria, specialized structures for the transfer of nutrients and signals between host and pathogen. Management of downy mildew in Europe requires the use of tolerant cucurbit cultivars in conjunction with fungicide applications. In the USA, an aggressive fungicide programme, with sprays every 5-7 days for cucumber and every 7-10 days for other cucurbits, has been necessary to control outbreaks and to prevent crop loss. (Day Laboratory website with research advances in downy mildew); (Hausbeck Laboratory website with downy mildew news for growers); (Cucurbit downy mildew forecasting homepage); (Downy mildew information for Michigan's vegetable growers). [ABSTRACT FROM AUTHOR]

To determine the effects of solar radiation on the survival of sporangia of Pseudoperonospora cubensis, the cause of cucurbit downy mildew, detached sporangia of P. cubensis were either exposed to the sun or placed in the shade from 08·00 to 17·00 h on sunny and cloudy days at Raleigh, North Carolina, in experiments conducted weekly from 9 July to 8 October 2008. Sporangia were assessed for germination every hour following exposure and germination was normalized based on the germination percentage of unexposed sporangia from the same collection. Exposure for a 9-h period, either in the sun or in the shade, significantly ( P < 0·0001) reduced normalized germination of sporangia. Decrease in normalized germination was significantly ( P < 0·0001) higher for sporangia exposed to the sun than sporangia in the shade, with the decrease being more rapid on sunny days than on cloudy days. On sunny days, solar radiation strongly reduced germination of sporangia ( β = −3·51), whilst on cloudy days, reduction in germination of sporangia was minimal ( β = −0·77). On sunny days, an exponential decay model, y = 95·2exp(−0·10 x), provided a significant ( R2 = 75·4%, n = 81, P < 0·0001) quantitative description of the effect of solar radiation dose on the percentage of normalized germination of sporangia. The effective cumulative solar radiation dose to inactivate 95% of the sporangia on sunny days was 29·5 MJ m−2. Disease severity data from inoculation experiments using sporangia exposed to varying amounts of cumulative solar radiation doses corroborated the results of the solar radiation experiments. [ABSTRACT FROM AUTHOR]

The article presents a study on risk resistance in Pseudoperonospora cubensis to fungicide flumorph in vitro. It focuses on the oomycete fungicide flumorph as a recent addition to carboxylic acid amide (CAA) fungicide. The risk in developing field resistance to flumorph is explored and compared with dimethomorph and azoxystrobin. Level of resistance in the procedure is described. Results and findings are presented in brief focusing on resistant isolates and cross-resistance mechanism with an attempt to generate mutants.

Plastic-house experiments were conducted over a 2-year period (2004–05) to estimate the effects of successive applications of flumorph or a mixture of flumorph with mancozeb to cucumber plants on selection for flumorph resistance in the downy mildew oomycete, Pseudoperonospora cubensis. Application of flumorph alone favoured the selection of resistant isolates of Ps. cubensis. Resistant populations were detected at a frequency of 2·5% after six successive applications of flumorph alone in a plastic house in 2004. Resistant isolates were also detected (4·8%) after eight successive applications of the mixture of flumorph and mancozeb in 2004, although the mixture gave significantly better disease control than flumorph alone and produced a slight delay in the development of resistance. In a second cucumber crop in the same plastic houses in 2004, the frequency of resistant isolates increased to 100% after three successive applications of flumorph or four of flumorph + mancozeb. Under laboratory conditions, most flumorph-resistant isolates showed high levels of resistance and their levels of pathogenicity and sporulation were as high as that of wild-type isolates. Flumorph showed cross-resistance with dimethomorph and iprovalicarb, but not with azoxystrobin, cyazofamid, cymoxanil or metalaxyl. These studies suggest a high risk for the occurrence of resistance to flumorph in Ps. cubensis in cucumber crops under plastic-house conditions. [ABSTRACT FROM AUTHOR]

During the growing seasons between the years 2001 and 2004, 98 isolates of Pseudoperonospora cubensis from nine regions of Czech Republic were collected and screened for tolerance/resistance to the three frequently used fungicides (propamocarb, fosetyl-Al, metalaxyl). Fungicides were tested in five different concentrations, using a floating disc bioassay. Fungicide effectiveness varied considerably. Propamocarb appeared most effective and all the isolates collected in the years 2001–2003 were found sensitive to all tested concentrations [607–9712 μg active ingredient (a.i.)/ml]. In 2004, some strains with increased resistance to propamocarb were detected. These strains were characterized by tolerance at the lowest concentrations (607 μg a.i./ml, eventually on 1214 μg a.i./ml); however, they were controlled by 2428 μg a.i./ml. Fosetyl-Al was effective at the recommended concentration of 1600 μg a.i./ml against all isolates. However, the occurrence of isolates (collected in 2001) which sporulated at low concentrations (400 and 800 μg a.i./ml) indicated that the selection for tolerance occurs in the pathogen population. Nevertheless, this phenomenon was not confirmed with the P. cubensis isolates collected between the years 2002 and 2004. Metalaxyl was found ineffective, because 97% of the isolates showed the resistance to the recommended concentration (200 μg a.i./ml), and the other 3% of isolates expressed tolerant response. The majority of the isolates showed profuse and/or limited sporulation at higher concentrations (400 and 800 μg a.i./ml). A substantial shift to highly metalaxyl resistant strains was evident in the Czech P. cubensis populations during 2001–2004. [ABSTRACT FROM AUTHOR]

Cucurbit downy mildew, caused by Pseudoperonospora cubensis, is among the most devastating diseases of cucurbitaceous plants. In spite of improved cultural practices and breeding for resistant cultivars, chemical control is still a very important tool to manage the disease. During the last several decades, many fungicides from various chemical classes have been developed. The occurrence of strains of P. cubensis resistant/tolerant to some fungicides encouraged research of this phenomenon. The first part of this article summarises the many different methodological approaches such as field trials, in vitro testing on active plant tissues or molecular diagnoses developed for the detection of resistant/tolerant strains of P. cubensis, as well as methods to collect and maintain pathogen isolates. The second part outlines the commonly used fungicides to control P. cubensis and their features like systemicity, biological and biochemical mode of action and translocation behaviour within plants. The last part deals with geographical aspects such as first appearance of resistance problems, distribution of resistance, temporal development of resistance under selection pressure by a fungicide, fitness of resistant subpopulations in competition with sensitive ones in the absence of a fungicide, as well as genetic and molecular sources of resistance. [ABSTRACT FROM AUTHOR]

Cyazofamid (ISO proposed common name), 4-chloro-2-cyano-2V,2V-dimethyl-5-/>-tolylimi-dazole-1-sulfonamide is a novel fungicide exhibiting specific activity against diseases caused by Oomycetes. In tests, cyazofamid at 0.4-1.6mg litre-1 exhibited excellent preventative activity against Phytophthora infestans on tomato and Pseudoperonospora cubensis on cucumber. Minimum inhibitory concentrations of cyazofamid against both diseases were over 63 times lower than those of mancozeb and at least 16 times lower than those of metalaxyl. Cyazofamid at 1.6-25 mg litre-1 exhibited not only preventative activity, but also stable residual activity and rainfastness. Cyazofamid at 6.3mg litre-1 reduced zoosporangia formation of P infestans and P cubensis on host plants by 100 and 94% respectively. Cyazofamid also exhibited translaminar and curative activity. Cyazofamid has a new mode of action for fungicides and exhibits no cross-resistance with other currently registered and commonly used fungicides. These properties lead to a high level control by cyazofamid in field. [ABSTRACT FROM AUTHOR]

A rapid assay for monitoring peroxidase activity in melon as a marker for resistance to Pseudoperonospora cubensis was developed. A high correlation was demonstrated between peroxidase activity and resistance in test wells containing leaf disks of melon plants with known levels of susceptibility or resistance to P. cubensis. The possibility of using such an assay for a preliminary selection of melons resistant to P. cubensis is suggested. [ABSTRACT FROM AUTHOR]

The hyphac of Pseudoperonospora humuli were examined at 3, 4, 5 and 6 days after inoculation of hop leaves. The structure and occurrence of lomasomes, centrioles, Golgi bodies, mastigonemes, crystalline inclusion bodies and invaginated mitochondria are discussed. [ABSTRACT FROM AUTHOR]

The part of the host plasmalemma invaginated around the haustorium of Pseudoperonospora humuli was examined after staining with (a) Uranyl acetate followed by lead citrate and (b) a mixture of phosphotungstic acid and chromic acid. It was also examined by using a tilting and rotating goniometer stage. After staining with uranyl acetate and lead citrate the membrane could only be detected on about 45 % of the periphery of the haustorium transected in a section and only the outer dark component of the triplet unit membrane structure could be detected. The use of phosphotungstic acid-chromic acid enabled the whole of the triplet membrane structure to be seen but did not enable the membrane to be detected over a greater percentage of the haustorium periphery than with the first procedure. The use of the goniometer stage resulted in the membrane being seen around 95% of the periphery of the haustorium. [ABSTRACT FROM AUTHOR]

Evaluates the effectiveness of using cultivars with increased resistance, applying fungicides and performing short-term forecasting of disease appearance to control Pseudoperonspora cubensis on cucumber in Ukraine. Predictors for downy mildew forecasting; Determination of critical days for development of disease; Yield of cucumbers under different schemes of protection with fungicides.

An abstract of the article "Pseudoperonospora cubensis causing downy mildew disease on Impatiens irvingii in Cameroon: a new host for the pathogen," by H. Voglmayr, M. Piatek, and D.C. Mossebo is presented.