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  • Author or Editor: K. Körösi x
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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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During the period of 1993-2001 chemical decontaminations of 24 SGs in the units 1-3 of the Paks NPP were carried out by a non-regenerative version of AP-CITROX technology, even in two or three consecutive cycles. A comprehensive investigation of the above decontamination method have revealed that the fundamental issues of analytical chemistry and corrosion science were not taken into consideration during the elaboration of AP-CITROX procedure. Therefore, the non-regenerative version of the technology utilized at Paks NPP can be considered to be not an adequate method for the chemical decontamination of any reactor equipments having large steel surfaces (e.g., SGs). As a consequence of the lack of the appropriate decontamination method, initiation of a R&D project focused on the elaboration of the required technology should not be postponed. In this paper, we present a brief overview on the fundamental issues of the technology development. Selected findings obtained in our laboratory on the field of the improvement of the AP-CITROX technology are also reviewed in order to demonstrate the crucial role of some selection criteria.

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