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  • Author: P. Doležal x
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Virulence and Mating Type of Phytophthora infestans Isolates in the Czech Republic

Abstract

To evaluate the frequency and stability of the occurrence of P. infestans races and mating types in the Czech Republic, 338 monosporic isolates were collected from 31 sites in different potato-growing areas from 2012 to 2014 and in 2016. In total, 142 isolates were evaluated for virulence and race structure using the detached leaflet assay on Black’s differential set, supplemented with cultivar Sarpo Mira and somatic hybrid REG 46F. With the exception of virulence for resistance genes R9 and Rpi-blb-1, all virulence genes were detected among isolates, with a predominance of genes R1, R3, R7, R10, and R11. Most isolates were virulent to five or more R-genes, with a mean virulence complexity of 7.1. Among the 38 races detected, the most commonly occurring races were 1.2.3.4.6.7.10.11 and 1.2.3.4.7.10.11. Of the 338 isolates tested by the pairing test and the cleaved amplified polymorphism sequence (CAPS) marker, 40% were of the A1 mating type and 60% were of the A2 mating type, with an A1 : A2 isolate ratio demonstrating the predominance of the A2 mating type each year of the survey.

Open access
Characterization of Ni-P coating prepared via electroless deposition on AZ31 magnesium alloy

Abstract

This work deals with the characterization of Ni–P coating prepared via electroless deposition on wrought AZ31magnesium alloy. For the application of electroless deposition was proposed and optimized a suitable pretreatment process of magnesium alloy surface followed by Ni–P coating in the nickel bath. The chemical composition of Ni–P based coating was characterized using the scanning electron microscope with chemical composition analysis. Next, physico-chemical properties and mechanical characteristics of Ni–P coating were evaluated. The mechanism of corrosion degradation of the coating and the substrate was also studied in this work.

Open access
Climate Change and its Impact on the Conditions of Late Blight Occurrence

Abstract

The paper is focused on the evaluation of trends in weather indicators influencing conditions for late blight occurrence, and subsequently on trends in the first treatment forecasts, number of infections, and number of infection days. The processing covering the period 1975–2016 was done with a higher density of points for the Czech and Slovak Republics and a lower density for European regions with more important distribution of potato growing on arable land. The obtained results show an unambiguous statistically significant trend in the increase of minimum temperature by around 0.5°C per 10 years; contrarily, no more significant trends were recorded for air humidity. For precipitation no statistically significant decreases were found at any of the processed localities, increases were rarely detected. Considering the number of days with precipitation, for the western part of the studied territory rather increases, while for the eastern part stagnation, and for Ukraine decrease in days with precipitation were recorded. Trends in the processed characteristics using the index method of late blight indicate a statistically more significant earlier onset of the first treatment especially at Czech localities; however, at most localities a slight increase in the number of infection periods and in the number of days with infection pressure was found.

Open access
Improvement of bio-compatible AZ61 magnesium alloy corrosion resistance by fluoride conversion coating

Abstract

Magnesium and its alloys are perspective bio-degradable materials used mainly due to their mechanical properties similar to those of mammal bones. Potential problems in utilization of magnesium alloys as bio-materials may relate to their rapid degradation which is associated with resorption problems and intensive hydrogen evolution. These problems can be eliminated by magnesium alloys surface treatment. Therefore, this work aims with analysis of the influence of fluoride conversion coating on corrosion characteristics of magnesium alloy. Unconventional technique by insertion of wrought magnesium alloy AZ61 into molten Na[BF4] salt at temperature of 450 °C at different treatment times was used for fluoride conversion coating preparation. The consequent effect of the coating on magnesium alloy corrosion was analyzed by means of linear polarization in simulated body fluid solution at 37 ± 2 °C. The obtained results prove that this method radically improve corrosion resistance of wrought AZ61magnesium alloy even in the case of short time of coating preparation.

Open access
Corrosion behavior of wrought magnesium alloys AZ31 and AZ61 in Hank’s solution

Abstract

Corrosion behavior of wrought magnesium alloys AZ31 and AZ61 was studied in Hank’s solution. Potentiodynamic curves measured after short-term of exposure showed higher corrosion resistance of AZ31 magnesium alloy in comparison with AZ61 magnesium alloy. On the contrary, long-term tests measured by electrochemical impedance spectroscopy showed higher corrosion resistance of AZ61 magnesium alloy in comparison with AZ31 magnesium alloy.

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Evolution of microstructure and electrochemical corrosion characteristics of cold compacted magnesium

Abstract

The main advantage of magnesium and its alloys is high specific strength and biocompatibility. A modern approach to magnesium-based materials preparation is powder metallurgy. This technique allows preparation of new materials with a unique structure, chemical composition, and controlled porosity. In this study, cold compaction of magnesium powder was studied. Magnesium powder of average particle size of 30 μm was compacted applying pressures of 100 MPa, 200 MPa, 300 MPa, 400 MPa and 500 MPa at laboratory temperature. Influence of compacting pressure was studied with microstructural and electrochemical corrosion characteristics analysis. The resulting microstructure was studied in terms of light and electron microscopy. Obtained electrochemical characteristics were compared with those of wrought magnesium. Compacting pressure had a significant influence on microstructure and electrochemical characteristics of prepared bulk magnesium. With the increase in compaction pressure, the porosity decreased. Compacting pressures of 300 MPa, 400 MPa and 500 MPa led to the similar microstructure of the prepared material. Polarization resistance of compacted magnesium was much lower and samples degraded faster when compared to wrought magnesium. Also, the corrosion degradation mechanism changed due to the microstructural differences between the material states.

Open access