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  • Author or Editor: F. Virányi x
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The majority of plant pathogens comprising about 60% of the total are belonging to a group of eukaryotic microorganisms, commonly known as FUNGI although this name obviously covers a number of organisms that are not fungi in a strict sense (1(. Yet, all these plant pathogens, having different systematic positions within the livings, are of significance as far as agricultural crop production is concerned.Mycologists in the past were primarily interested in identifying fungal diseases, describing the fungi, studying their life cycle in relation to environment and looking for effective control measures. A big step forward was when investigations expanded toward the physiology of plant diseases and disease resistance. Meanwhile fungal genetics has developed providing a better understanding of plant-fungus relations. Recently, with the introduction of molecular techniques, new approaches of research, such as molecular taxonomy and molecular genetics have been established and the molecular methods were applied in other related fields of studies.For the illustration of changes in research interest worldwide, the main research topics and all the contributions (poster presentations) accepted at and published by the 7th International Congress of Plant Pathology held in Edinburgh, Scotland between 9-16 August 1998 have been scanned. Based on these, some of the most promising research trends with a few examples will be accounted here and then a short overview of what has recently been done by Hungarian mycologists on the subject will be given.

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The main objectives of this study were to determine which of the two overwintering forms of Erysiphe necator (either by hyphae in grapevine buds or via cleistothecia on leaf, cane or trunk surfaces) dominate in different vine-growing regions of Hungary, and to find out their impact on initiating disease epidemics. The only evidence of mycelial overwintering of this fungal pathogen in grapevine buds in 2004 was found in a vineyard in Sióagárd where one single plant showed the typical symptoms of “flag shoot”, whereas in all other cases initial infections by ascospores from overwintering cleistothecia were evident. The appearance and spread of E. necator was quite similar in the vineyards of Eger, Kecskemét and Sióagárd, the first leaf symptoms appearing about three weeks before flowering, and by the time grape bunches became susceptible to powdery mildew attack, a significant amount of inoculum was available that resulted in up to 90–100% infection. Microscopical investigations revealed a relatively low percentage of parasitism of cleistothecia by Ampelomyces sp. in the grapevine cultivars examined.

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The aim of this study was to develop an accurate, fast and safe routine diagnostic method based on protein studies for differentiating between T. caries and T. controversa at species level. Since import of wheat contaminated with T. controversa is restricted by several countries, differentiation of T. controversa from the more prevalent T. caries is of economic interest. The newly developed method is based on distilled water washing followed by the rupturing of the teliospore walls in PBS extraction medium, and an SDS electrophoresis (10% resolving gel). The electrophoretic pattern showed consistent species-related differences in a 106 kDa polypeptide that appeared in each extract of T. controversa, but was not present in the protein extracts of T. caries. The newly developed method could be of value for the authorities performing routine monitoring of T. controversa as an up-to-date diagnostic assay in wheat shipments.

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Downy mildew of sunflower (Plasmopara halstedii) can be effectively controlled by either genetic resistance or chemical pesticides but the development of new pathogen genotypes may lead to a re-emergence of the disease. The aim of the present work was to determine whether chemical inducers of disease resistance such as dichloroisonicotinic acid (INA) and β-aminobutyric acid (BABA) induce resistance to downy mildew in susceptible sunflowers, and affect resistant responses in mildew-inoculated resistant sunflower lines. Treatments of 3-day-old seedlings with one of these chemicals significantly reduced downy mildew disease symptoms (sporulation, stunting) in susceptible plants, and inhibited systemic mycelial growth of the pathogen. Furthermore, host cellular responses, like necrosis and secondary cell division became evident at infection sites. These effects are similar to those found in previous studies with benzothiadiazole, and closely resemble defense responses in sunflower plants carrying P. halstedii resistance genes. Under in vitro conditions, these activators slightly inhibited the germination of zoosporangia.

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In the present work we aimed at comparing the effect of benzothiadiazole (BTH) treatment on defence reactions of sunflower plants to downy mildew and white rot diseases. BTH treatment resulted in reduced disease symptoms in biotrophic and in the early stage of the necrotrophic interactions. To get a better insight into the effect of BTH, changes in the activities of polyphenol oxidase and peroxidase enzymes, as well as the expression of the host response-associated sunflower genes were examined in the plants. Inoculation with Plasmopara halstedii enhanced the polyphenol oxidase and peroxidase enzyme activities, while inoculation with Sclerotinia sclerotiorum did it only at 4 dpi. However, most importantly, in each case extracts from BTH pretreated and inoculated plants showed the highest polyphenol oxidase and peroxidase enzyme activities. Similarly, the accumulation of GST and PDF transcripts was detected following inoculations with both biotrophic and necrotrophic pathogens, and again, BTH pre-treatment enhanced GST and defensine gene activities in the inoculated plants. We suggest that induction of enzyme activities, as well as of the elevated expression of GST, PDF and PR5 genes by BTH pre-treatment may be a significant part of the induced resistance of sunflower to downy mildew and white rot (white mold).

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Effects of habitat characteristics and climatic factors on the occurrence of reed pathogens were investigated in a four-year survey. While diseases caused by Puccinia magnusiana, Polythrinciopsis phragmitis and Stago­no­spora sp. started to increase as early as in August, the other species caused severe infection in September (Deightoniella arundinacea, Puccinia phrag­mitis) or even later in the vegetation period (Deightoniella roumeguerei). For the distribution of some fungal pathogens (Puccinia phragmitis, Deighto­niella arundinacea, D. roumeguerei and Stagonospora sp.) weather conditions (especially precipitation) were profound, while the occurrence of others (Puccinia magnusiana and Polythrinciopsis phragmitis) depend­ed more on the characteristics of reed stands.

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