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. (2010) A total of 195 isolates of Phytophthora infestans were collected from late blight-diseased potatoes grown in several localities in the Czech Republic during the years 2007-2008. The isolates were analysed for mating type using the pairing test, CAPS marker assays and PCR assays. Of the 195 tested isolates, 28% were of the A1 mating type and 75% corresponded to the A2 mating type. Furthermore, oospores of P. infestans were microscopically detected in leaf samples from one locality.

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.

A total of 235 Phytophthora infestans isolates were collected from five regions of the Czech Republic during the growing seasons 2012-2014 and 2016 and examined using the in vitro amended agar method for their sensitivity to metalaxyl-M (MFX), propamocarb-HCl (PCH), and dimethomorph (DMM). A majority of the isolates (50%) were sensitive to MFX. Resistant isolates were found in all four years of the survey; they represented 30% of the samples. The EC 50 values of PCH in inhibiting mycelial growth of 65% of the overall isolates were higher than 100 µg ml -1 , which indicates the occurrence of insensitivity to PCH in the Czech P. infestans populations. DMM was very effective, and the mycelial growth of all isolates tested was completely suppressed at the concentration of 0.1 μg ml -1 . Furthermore, the efficacy of 12 plant essential oils was tested against 20 isolates of P. infestans using the in vitro amended agar method. Essential oils of Cymbopogon winterianus, Litsea cubeba, Mentha spicata, Pelargonium graveolens, Syzygium aromaticum, and Thymus vulgaris were observed to have the highest antifungal activity against P. infestans, with minimal inhibitory concentrations less than or equal to 1 µl ml -1 . dimethomorph, aromatic plants, fungicide resistance, late blight, metalaxyl-M, propamocarb-HCl

Adequate integrated management of potato leaf diseases can have an influence on pathogens which are challenging to control and cause main potato tuber diseases. Deriving from this hypothesis, an experiment was designed to evaluate the efficacy of foliar application of twelve fungicides on late blight in tubers, common scab, black scurf and silver scurf. In the period of 2013 to 2017, the fungicides were equally applied six times in registered doses during the growing seasons. Eight tuber disease indicators and eight yield characteristics were then evaluated in harvested tuber samples. Significant differences were found among the fungicides used. In comparison to the negative control (n. c.), the application of Infinito, Ranman Top and Revus Top reduced the quantity of tubers infected by late blight by 72% on average. The incidence of common scab increased by 65% of n. c. under the effect of copper oxychloride, while an average reduction by 19% of n. c. was observed with the use of Acrobat MZ WG, Curzate Gold and Consento. The occurrence of silver scurf was significantly enhanced by Curzate Gold and Consento (105% of n. c.), while it was suppressed by Revus Top and Revus (85% of n. c.). All fungicides were ineffective on black scurf yet had a positive influence on the potato yield and quality, with the choice of fungicide having a great impact on the quality of tubers. The application of any safe fungicide is important, especially in years similar to 2015, which was the most devastating recent year for potato production in terms of structural changes in yield of tubers.