The diploma thesis deals with ash dieback caused by pathogenic agent Hymenoscyphus pseudoalbidus. This pathogenic fungus has spread across the whole Europe during the last twenty years and became a serious threat for European ash populations (Fraxinus sp.). This work is mainly focused on H. fraxineus symptomatology in relation to phenology of Fraxinus excelsior L. in situ. Artificial infectious experiments were carried out and several control measures were tested. The methodology of inoculation with ascospores and methodology of evaluation of ash stands infected by H. fraxineus were designed. Outside the terms of assignment of this thesis, the speed of infection spread and mortality rate in stands of different ages were observed. One of the most interesting results is a finding that severe infection causes significant slowdown of phenological phases of F. excelsior. Infectious experiments showed high susceptibility of F. excelsior to the infection. The infection broke out in 83.7% of tested individuals. The susceptibility of F. pensylvanica and F. americana was proved to be considerably lower.

This thesis deals with a survey of provenance areas and assessment of attacking Fraxinus excelsior L. and Fraxinus angustifolia by the pathogen Hymenoscyphus fraxineus. The aim of the thesis is to map the incidence of infected trees in these areas and to evaluate the sensitivity of the sites to the pathogen Hymenoscyphus fraxineus. The theoretical part deals with processing of data collected during field work on selected provenance areas Koneprusy and Veltruby. Amongst the evaluated parameters there were: trunk diameter at measuring height, tree height, and especially canopy drying caused by Hymenoscyphus fraxineus. As the outcome of the survey photographs were taken and records were collected for individual trees in the provenance areas. Each of the trees has its own unique label that has accurately defined its location to prevent potential errors in data processing. The processed data was then evaluated in NCSS 8.0 software and cluster analysis was performed in order to compare the provenances. This analysis only compares the provenances, which are located in both provenance areas. The results show that no provenance without the pathogen Hymenoscyphus fraxineus attack appeared in the provenances Koneprusy and Veltruby. Subjects in 4 ŠLP Kostelec nad Černými Lesy - Svojšice and 24 LS Czech Krumlov Chvalšiny proved to be more resistant than others. Although the increase in the tree height and the trunk thickness is the largest on those areas the defoliation rate is high. It is probable that the population of these provenances will gradually die. Due to growing abbility of some individuals located in other provenances it is obvious that habitat conditions and individual resilience are key factors.

Diploma thesis deals with ash dieback, caused by fungus pathogen Hymenoscyphus fraxineus. This is a summary of the available knowledge in literature concerning the problematic of the disease. Research activities were focused on monitoring of this patogen spread in the area of Moravia and eastern Bohemia, with emphasis on forest-typological diversity of habitats and the percentage of ash in the stands. 434 stands of ash were evaluated and the rate of health condition damage of trees with H. fraxineus presence depending on various factors was investigated. Dependence of damage of health status was not determinated as a function of LVS of Plíva (1987) (forest vegetation altitude stage), edaphic category or ecological range of Plíva (1987) as well as age stage of ash, stocking, other tree species composition, location and year of evaluation. Vice versa factors of damage on nature of ashes sites (SLT according Plíva 1987), mixing type and forest regeneration type were significant.

This diploma thesis is interested in effective defense against necrosis of ashes. This disease influ-ences the ash population throughout whole Europe at present. Part of the diploma thesis is inte-rested in function of the ash patosystem. Within this research was realised complex analysis of the soil focused on physically-chemical and chemical atributes of the soil. On the partial variants were aplicated preparations with fungicidal behavior which were applied on the surface of the assimilation part of the plant. Substances should worked negative against successful germination of the ascospores on the leaves of the affected trees. In the second direction of the research was used nitrogen fertilizers which should positively influenced vitality of the host trees and together accelerated decomposition infected saps on the soil surface. Efficiency of defensive measures was evaluated with help of the periodical evaluation of health condition of the treated trees on the research areas. To this rating was used methodology Health condition the forest of ashes evaluation (Rozsypálek, 2015). Efficiency of the substance takes effect by braking or complete stopping worsening health condition. For stopping worsening health condition was recommended applying 20-25 l. ha concentrate Vermaktiv Stimul S16 with ionic sulfur in a higher proportion. Ratio of dilution with water is 1:50 – Vermaktiv S16 – water. As another active substance in relation with health vitality was evaluated ammonium sulfate. This application is implemented on the soil surface with recommended ration 750 kg. ha which represents 150 kg pure nitrogen per 1 ha.