The cultivation and production of cucumber are seriously affected by downy mildew caused by Pseudoperonospora cubensis. Downy mildew damages leaves, stems and inflorescences, and then reduces the yield and quality of cucumber. This review summarized the research advances in cucumber downy mildew, including pathogen detection and defense pathways, regulatory factors, mining of pathogens-resistant candidate genes, proteomic and genomic analysis, and development of QTL remarks. This review may facilitate clarifying the resistance mechanisms of cucumber to downy mildew.
Cucumis sativus/genetics* ; Oomycetes/genetics* ; Peronospora ; Plant Diseases/genetics* ; Proteomics

Many members of the Saprolegniales (Oomycete) cause mycoses and disorders of fishes, of which Achlya and Saprolegnia are most ubiquitous genera worldwide. During a survey of the diversity of freshwater oomycetes in Korea, we collected seven isolates of Achlya, for which morphological and molecular phylogenetic analyses enabled them to identify as Achlya americana and Achlya bisexualis. In Korea, only a species of Achlya, A. prolifera, has been previously found to cause seedling rot on rice (Oryza sativa), but none of the two species have been reported yet. Importantly, A. bisexualis was isolated from a live fish, namely rice fish (Oryzias sinensis), as well as freshwater, and this is the first report of Achlya-causing mycoses on freshwater fishes in Korea. The presence of A. americana and A. bisexualis on live fish in Korea should be closely monitored, as considering the well-known broad infectivity of these species it has the potential to cause an important emerging disease on aquaculture industry.
Achlya ; Aquaculture ; Fishes ; Fresh Water ; Korea ; Mycoses ; Oomycetes ; Saprolegnia ; Seedlings

A severe damping-off disease of bush okra caused by Pythium aphanidermatum, was diagnosed in plastic houses in Der Attia village, 15 km southwest of El-Minia city, Egypt, during the winter of 2001. Bush okra seedlings showed low emergence with bare patches inside the plastic houses. Seedlings that escaped pre-emergence damping-off showed poor growth, stunting and eventually collapsed. Examination of the infected tissues confirmed only Pythium aphanidermatum, showing its typical intercalary antheridia, and lobulate zoosporangia. P. aphanidermatum was shown to be pathogenic on bush okra under pot and field experiments. Bacteria making inhibition zones against the damping-off fungus P. aphanidermatum were selected. Agar discs from rhizosphere soil of bush okra containing colonies were transferred onto agar plate culture of P. aphanidermatum. After 2 days of incubation, colonies producing clear zones of non-Pythium growth were readily detected. The two bacteria with the largest inhibition zones were identified as Pseudomonas fluorescens. Bush okra emergence(%) in both pot and plastic houses experiments indicated that disease control could be obtained by applying P. fluorescens to the soil or coating the bacteria to the bush okra seeds before sowing. In the plastic houses, application of the bacteria onto Pythium-infested soil and sowing bush okra seeds dressed with bacteria gave 100% emergence. In addition, This was the first reported disease of bush okra by this oomycete in Egypt.
Abelmoschus* ; Agar ; Bacteria ; Egypt ; Fungi ; Oomycetes ; Plastics ; Pseudomonas fluorescens* ; Pseudomonas* ; Pythium* ; Rhizosphere* ; Seedlings ; Soil ; United Nations

The effect of four sub-lethal concentrations (400, 800, 1,200 and 1,600 microg/ml) of three amino acids such as isoluecine, aspartic acid and phenylalanine on vegetative growth and sexual and asexual reproduction of Achlya racemosa, A. proliferoides and Saprolegnia furcata was investigated. The density of vegetative growth and diameters of vegetative colonies of species of the Oomycetes fungi decreased with rising the concentration of the applied amino acid. Vegetative hyphae of treated fungi almost appeared branched in case of S. furcata, thick in case of A. racemosa and distorted in case of A. proliferoides as compared with control. The different treatments with amino acids depressed both sporangial formation and discharge, which were dependent on the tested species of zoosporic fungi, the amino acid and its dosage. Phenylalanine was the most effective amino acid in inhibiting sporulation and S. furcata was the most sensitive fungal species. Aspartic acid and isoleucine stimulated germination of discharged spores through the formation of germlings. Gemmae formation by the three fungi was reduced at the low concentrations of amino acids and nearly missed at high concentrations. Sex organs (oogonia and antheridia) were affected partly; rudiment oogonia were observed at low concentrations (400 and 800 microg/ml) and disappeared at higher concentrations, whereas antheridial branch formation was stimulated as the fungi were treated with isoleucine and to some extent phenylalanine.
Achlya* ; Amino Acids* ; Aspartic Acid ; Fungi ; Germination ; Hyphae ; Isoleucine ; Oogonia ; Oomycetes ; Phenylalanine ; Reproduction, Asexual ; Saprolegnia* ; Spores

OBJECTIVETo study the pathogen of opium poppy downy mildew and its biological characteristic for further research on the disease.

METHODDevelopment of the disease was observed systematically in the field. Germination rate of sporangium in different temperature, pH and nutrition was examined with suspending-drop method. Slide-germination method was used to observe its germination in different humidity maintained by different concentration of H2SO4.

RESULT AND CONCLUSIONThe disease manifests itself in two forms: severely infected plants (systematic infection) and leaf spots (nonsystematic infection). Sporangia of the pathogen are oval or globular, thin walled, smooth, hyaline, with 7.74-16.34 microns diameter in base 1 and 8.34-15.05 microns in base 2.0 ospores are light yellow with 33.87-70.54 microns x 19.34-62.64 microns in base 1 and 36.85-49.68 microns x 42.08-55.76 microns in base 2. Conidiophores are stout, erect, whose branching times and length are different between those in base 1 and those in base 2. Sporangia sprot directly in two hours. Film of water is necessary for sporangium to sprot. The optimum temperature range of sporangium sprot is 12-21 degrees C, the best being 16 degrees C, the pH range is 4.53-9.18 the best optimum at pH 7.38, and the extract of leaf of 1:5 is good for its germination.

Humidity ; Hydrogen-Ion Concentration ; Oomycetes ; growth & development ; ultrastructure ; Papaver ; microbiology ; Plant Diseases ; microbiology ; Spores, Fungal ; growth & development ; ultrastructure ; Temperature

OBJECTIVETo screen effectual fungicides for field control because of the seriousness of opium poppy mildew and importance of chemical control on plant diseases.

METHODSeven fungicides were screened in Lab experiment and field test during 1996-1997.

RESULT AND CONCLUSIONAll of them and their different dosages were effective to control conidia of Peronospora arborescens. Among them, 72.2% propamocarb of 1203 and 902.5 ppm were the most effective both in Lab experiment and field test with efficacy 79.91% and 79.33% respectively in field test, and the efficacy of other fungicides was over 50%. Seven fungicides tested can be used to control nonsystematic symptom of opium poppy mildew.

Carbamates ; pharmacology ; Fungicides, Industrial ; pharmacology ; Oomycetes ; drug effects ; pathogenicity ; Papaver ; microbiology ; Plant Diseases ; microbiology ; Plants, Medicinal ; microbiology

The genus Peronospora, an obligate biotrophic group belonging to Oomycota, causes serious damage to a variety of wild and ornamental plants, as well as cultivated crops, such as beet, rose, spinach, and tobacco. To investigate the diversity of Peronospora species parasitic to Stellaria and Pseudostellaria (Caryophyllaceae) plants in Korea, we performed a morphological analysis on dried herbarium specimens and molecular phylogenetic inferences based on internal transcribed spacer rDNA and cox2 mitochondrial DNA sequences. As a result, it was confirmed that there are four species of Peronospora parasitic to specific species of Stellaria and Pseudostellaria, all of which were hitherto unrecorded in Korea: P. alsinearum (ex Stellaria media), P. stellariae-aquaticae (ex Stellaria aquatica), P. stellariae-uliginosae (ex Stellaria alsine), and P. pseudostellariae (ex Pseudostellaria palibiniana). In addition, Peronospora specimens parasitic to Pseudostellaria davidii differed morphologically from P. pseudostellariae owing to the large and ellipsoidal conidia; this morphological discrepancy was also validated by the high genetic divergence between the two species. Peronospora casparyi sp. nov. is described and illustrated here.
Beta vulgaris ; Caryophyllaceae ; Classification* ; DNA, Mitochondrial ; DNA, Ribosomal ; Host Specificity ; Korea* ; Oomycetes ; Peronospora* ; Phylogeny* ; Spinacia oleracea ; Spores, Fungal ; Stellaria* ; Tobacco

The effects of different concentrations of three amino acids as carbon and or nitrogen sources on mycelial dry weights, changes in pH values of synthetic medium, ammonia secretion and extracellular protease activity by three zoosporic fungi, pathogens of fish and shellfish, were studied. As compared with the control, the addition of isoleucine and aspartic acid as nitrogen sources were generally stimulative for mycelial dry weight production whereas phenylalanine was inhibitory irrespective to the tested fungal species. When amino acids served as carbon and nitrogen sources, the mycelial dry weights of the three fungi were increased (mostly non-significantly) relative to untreated control but weights were decreased as the concentrations of the three amino acids raised. The addition of individual amino acids as carbon and nitrogen sources to the medium significantly increased pH values of the medium comparable to the control. The addition of each of the three amino acids as carbon and nitrogen sources to the medium significantly induced ammonia secretion by the three species of zoosporic fungi. Ammonia secretion in synthetic medium amended with amino acids as nitrogen source raised by the three zoosporic fungi relative to untreated control except in case of Achlya racemosa treated with isoleucine. Extracellular protease activity was almost promoted in case of Achlya proliferoides and Saprolegnia furcata cultures treated with isoleucine and aspartic acid individually in presence of glucose and vice versa in case of phenylalanine. However, extracellular protease activity of A. racemosa decreased compared with the control at various concentrations of isoleucine and both phenylalanine and aspartic acid assumed inconsistent effects. Extracellular protease activity of the three zoosporic fungi in the medium devoid of glucose varied depending upon zoosporic fungal species, the tested amino acid and the applied concentrations. The values of protease activity were approximately less two folds than that obtained in presence of glucose.
Achlya ; Amino Acids* ; Ammonia* ; Aspartic Acid ; Carbon ; Fungi ; Glucose* ; Hydrogen-Ion Concentration ; Isoleucine ; Nitrogen ; Oomycetes* ; Phenylalanine ; Saprolegnia ; Shellfish ; Weights and Measures

Thailand is one of the largest citrus producers in Southeast Asia. Pathogenic infection by Phytophthora, however, has become one of major impediments to production. This study identified a pathogenic oomycete isolated from rotted roots of pomelo (Citrus maxima) in Thailand as Phytophthora nicotianae by the internal transcribed spacer ribosomal DNA sequence analysis. Then, we examined the in vitro and in vivo effects of Chaetomium globosum, Chaetomium lucknowense, Chaetomium cupreum and their crude extracts as biological control agents in controlling this P. nicotianae strain. Represent as antagonists in biculture test, the tested Chaetomium species inhibited mycelial growth by 50~56% and parasitized the hyphae, resulting in degradation of P. nicotianae mycelia after 30 days. The crude extracts of these Chaetomium species exhibited antifungal activities against mycelial growth of P. nicotianae, with effective doses of 2.6~101.4 microg/mL. Under greenhouse conditions, application of spores and methanol extracts of these Chaetomium species to pomelo seedlings inoculated with P. nicotianae reduced root rot by 66~71% and increased plant weight by 72~85% compared to that in the control. The method of application of antagonistic spores to control the disease was simple and economical, and it may thus be applicable for large-scale, highly effective biological control of this pathogen.
Asia, Southeastern ; Biological Control Agents* ; Chaetomium* ; Citrus* ; Complex Mixtures ; DNA, Ribosomal ; Hyphae ; Methanol ; Oomycetes ; Phytophthora* ; Plants ; Seedlings ; Sequence Analysis ; Spores ; Thailand ; Tobacco*

NADPH oxidases (Noxes), transmembrane proteins found in most eukaryotic species, generate reactive oxygen species and are thereby involved in essential biological processes. However, the fact that genes encoding ferric reductases and ferric-chelate reductases share high sequence similarities and domains with Nox genes represents a challenge for bioinformatic approaches used to identify Nox-encoding genes. Further, most studies on fungal Nox genes have focused mainly on functionality, rather than sequence properties, and consequently clear differentiation among the various Nox isoforms has not been achieved. We conducted an extensive sequence analysis to identify putative Nox genes among 34 eukaryotes, including 28 fungal genomes and one Oomycota genome. Analyses were performed with respect to phylogeny, transmembrane helices, di-histidine distance and glycosylation. Our analyses indicate that the sequence properties of fungal Nox genes are different from those of human and plant Nox genes, thus providing novel insight that will enable more accurate identification and characterization of fungal Nox genes.
Biological Processes ; Computer Simulation* ; Eukaryota ; Genome ; Genome, Fungal ; Glycosylation ; Humans ; NADP ; NADPH Oxidase* ; Oomycetes ; Oxidoreductases ; Phylogeny ; Plants ; Protein Isoforms ; Reactive Oxygen Species ; Sequence Analysis*