Analysis of selected factors affecting the occurrence of Chalara fraxinea in the environment.

The dissertation thesis is aimed to identify the environmental and other factors responding for development of the disease caused by the invasive alien pathogen Hymenoscyphus fraxineus with use of statistical approach. It was supposed that many environmental factors and different characteristics of vegetation are involved in the epidemiology and in the disease impact. The investigation was performed in highly heterogeneous landscape of Lusatian Mts. where common ash is highly abundant and, moreover, the pathogen population is established. The field investigation was performed during 2011 -- 2013 in different vegetation types in the rural landscape (solitaires, scattered plantations, riparian stands, scree forests and mixed ash-alder alluvial forests). There were established 80 permanent plots in the area and in total 35 variables were evaluated in them: the rate of ash dieback (dependent variable), 20 independent variables describing the host presence and its other characteristics and 14 independent variables describing the environment. The developed GLM model explained ca 27% ofdisease variation. Particular models developed for vegetation types differed importantly from each other and explained 28 -- 46% of the disease variability. For instance it was found out that the rate of ash in the stands, canopy closure and other factors positively affected the disease impact whereas the tree height, slope etc. had the negative effect on the disease development. The influence of other pathogens and first of all the air humidity were identified as highly important. The hypothesis that the environmental factors importantly influence the disease impact was fulfilled

Analysis of selected factors affecting occurrence of Chalara fraxinea in the environment.

Extensive investigation of ash dieback impact on different rural vegetation types (solitaires, scattered plantations, riparian stands, scree- and ash-alder alluvial forests) was performed in the Lusatian Mts. (the Czech Republic) between 2011 and 2013. The rate of ash dieback and 27 environmental variables were investigated in 80 research plots with a total of 1045 evaluated trees. The developed model (GLM) explained ca 27% of the disease variability. Particular models for each vegetation type importantly differed from each other and explained 28--46% of the disease variability. The variables that positively affected the disease impact included the host crown area, ash area and rate of ash in the stands, tree layer area, canopy closure, north aspect, shrub and herbaceous layer canopy, vertical heterogeneity and standard deviation of TPI. Tree height, the distance and damage of the nearest host as well as the water source distance, slope and its standard deviation affected it negatively. The coincidental attack of the trees by Armillaria sp. and Hylesinus fraxini positively affected the disease progress, whereas the presence of Nectria sp. and Aceria fraxinivorus conclusively decreased progress, most likely via the induction of secondary metabolites. The highly conclusive regression of ash dieback on the number of days with an air humidity of >95% between 6--11 a.m. in the main period of ascospore spread was identified. Because the air humidity near the ground was highly affected by local factors, a GLM model explaining the variability of air humidity with that of investigated factors was developed. This model explained 77% of the variability attributed to air humidity, local factors (TPI and SD of TPI, aspect, slope, altitude, distance from open water, tree and shrub layers canopy, tree stand height, etc.) greatly affected the disease impact related to air humidity. The landscape form was identified as a factor (most likely via air humidity) that affects the impact of the disease -- for example, the stands on mountain tops and slopes were less affected than the stands in valleys. The vegetation types highly differed in the disease extent. In general, the solitaires and scree forests were significantly less damaged than mixed ash-alder forests and riparian stands. The smaller stands were less affected than the more extended, the stands enclosed in canopy of other forests were less damaged than comparable vegetation in open landscapes and stands with higher humidity (riparian stands and mixed ash-alder forests) were more damaged than those without water. The outcome clearly supports the possibility of development and usefulness of appropriate forest and landscape management of the disease

Micropropagation of common ash (Fraxinus excelsior L.)

The aim of the methodology is to provide an optimized process of micropropagation of common ash, which can support the production of its elite genotypes with a higher degree of tolerance to the invasive fungal pathogen Hymenoscypus fraxineus causing our domestic species of ash (Fraxinus excelsior and F. angustifolia) so called necrosis of ashes (known in Europe as " ash dieback "). The methodology includes two integrated in vitro propagation techniques, which are based either on juvenile plant material (from seeds) or on adult trees using apical buds

Potential risk of occurrence of <i>Phytophthora alni</i> in forests of the Czech Republic

<p><i>Phytophthora</i><i>alni</i> is an invasive organism that causes root and collar rot in alders, which significantly damages the forest and riparian vegetation of alder trees in Central and Western Europe. In the Czech Republic, this pathogen was first confirmed in 2001, and since then it has been gradually spreading from the west to the east. Here, we applied a model of potential distribution that estimates the level and spatial variability of the pathogen occurrence and spread risk for Czech Republic forests to target the early detection and control the further invasion of <i>P. alni</i> in this region. Our predictions are based on a rigorous statistical analysis of data obtained from field survey as well as available geodatabases. We used two sets of predictor variables describing (i) the forest stands and (ii) neighbourhood of the stands, and generalized linear modelling with forward stepwise selection of predictors. The results of statistical analysis showed the significant effect of the area of the forest stand, forest vegetation zone, presence of watercourse and area of alder stands in the neighbourhood on the probability of occurrence of <i>P. alni</i> in the study region. The map derived based on the final model shows the potential risk of occurrence and impact of <i>P. alni</i> in forests of the Czech Republic as classified on a five-point scale ranging from very low risk for alder stands with a low level of likely invasion to very sensitive alder stands with high probability of pathogen occurrence and high levels of damage. This is a unique output not only for the Czech Republic but also throughout Europe.</p