The epidemiology of potato late blight (Phytophthora infestans) was observed over the three-years with 110 potato varieties from various maturity groups treated or not treated with fungicides. The determined severity values were transformed into AUDPC coefficients characterizing rate of disease spreading across the crop in connection with varietal characteristics, fungicide application and year effects. The analysis of the pathogen population for the distribution of races virulent to usually used resistance genes indicated non-efficiency of these genes; resistance could only be increased by breeding for polygenically determined horizontal resistance. There were important yearly variations observed for the epidemiology of P. infestans. A correlation was detected between increasing AUDPC value and yield reduction in both fungicide treated and non-treated variants. AUDPC value of the treated variant is to a certain extent positively correlated with the value of the non-treated variant. However, particular interaction between potato genotype and applied fungicide program was shown, which could positively or negatively affect disease course in dependence on the variety.

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MAZÁKOVÁ J., TÁBORSKÝ V., ZOUHAR M., RYŠÁNEK P., HAUSVATER E., DOLEŽAL P. They were analysed for mating type using the conventional pairing assay and PCR markers; 107 isolates were of A1 and 92 of A2 mating type. No self-fertile isolate was found. Our study is the first report of the presence and distribution of the A2 mating type of P. infestans in the Czech Republic. The co-existence of the two mating types may enable the pathogen to reproduce sexually, thus enhancing the diversity of its population countrywide.

Beauveria bassiana (Balsamo) Vuillemin is a fungus with broad spectrum insecticidal activity. As a biological control agent used against Colorado potato beetles (Leptinotarsa decemlineata (Say)), this fungus has performed erratically in various field studies. This inconsistent performance has been attributed to formulation problems, UV sensitivity, and humidity. In a multi-site test, B. bassiana controlled Colorado potato beetle larvae in both Poland and the Czech Republic, but not in Maryland. Control was measured by reduction in populations of beetle larvae. One of the major differences among these sites was temperature. In Poland, the mean temperature ranged from 5°C to 23°C; in the Czech Republic the average temperature ranged from 6.7°C to 18.7°C; and in Maryland, temperatures at time of application exceeded 45°C at canopy level. This led us to examine B. bassiana growth in vitro.While B. bassiana grew in the laboratory from 16 to 30°C, the B. bassiana from a formulated product (Mycotrol™, Mycotech, Butte, MT) did not germinate at temperatures above 37°C. Germination and subsequent development of this entomopathogenic fungi are critical factors in the infection and control of the Colorado potato beetle. As a consequence of the inability to germinate at high temperatures, B. bassiana would not be expected to effectively control pest insects in climates with hot summers. This fungus, however, may be suitable for insect control in early spring or in cool temperature climates during the growing season.

Mazáková J., Zouhar M., Ryšánek P., Táborský V., Hausvater E., Doležal P. In the growing seasons from 2003 to 2008, 547 isolates of Phytophthora infestans from five regions in the Czech Republic were collected and examined for their sensitivity to the active ingredients (metalaxyl, dimethomorph and propamocarb-HCl) of frequently used fungicides. The response of the isolates to each of these substances was examined using the in vitro amended-agar method; in 352 of these isolates, the sensitivity to metalaxyl was also assessed by the floating leaf-disc assay. The majority of the isolates were sensitive (89.8%) to metalaxyl. All the isolates that were tested were sensitive to dimethomorph and propamocarb-HCl; these particular substances completely suppressed mycelial growth at 1 µg a.i. per ml.