Genetic variation of Fraxinus excelsior half-sib families in response to ash dieback disease following simulated spring frost and summer drought treatments

Ten juvenile Fraxinus excelsior half-sib families from two Lithuanian populations have been tested in the controlled environment for their response to ash dieback disease caused by Hymenoscyphus fraxineus, detecting changes of genetic variation and heritability, as well as estimating genotype by environment (G×E) interaction and phenotypic plasticity following artificial spring frost and summer drought treatments. In 2014, a batch of 200 four-year-old ash seedlings was used for each treatment and control (no treatment). Health condition, bud flushing phenology and height were assessed for each seedling, and disease incidence and survival ratios were assessed for each family both before (at the beginning of the vegetation season) and after the treatments (at the end of the vegetation season). Disease incidence ratio increased from 0.77-0.80 up to 0.90-0.95. Tree mortality rates during one vegetation season were significantly lower in the frost treatment (21%) than in the drought treatment (25%) or control (31%). None of the tested F. excelsior families were completely resistant to ash dieback, although significant among-family differences in disease incidence and damage rates suggest an additive mode of gene action and thus a quantitative resistance to the disease. Neither disease incidence rates, nor tree health condition scores differed significantly among the applied treatments (including control) indicating in general a negligible effect of the simulated adverse conditions on health status of the ash seedlings. However, G×E interaction was found to be significant (at P > 0.05) for disease incidence, length of necrotic shoots and tree survival, implying that susceptibility of ash families to the dieback disease unequally depends on environmental conditions, and indicating a presence of genetic variation in plasticity and reaction norms of the tested families across environments (treatments). Substantially increased coefficients of additive genetic variation and heritability in health condition following both frost and drought treatments and compared to control showed that simulated stress conditions may noticeably contribute to expression of differences among the tested F. excelsior families in their resistance traits, thus enabling a better evaluation of performance of different families, an effective family selection for resistance, and achievement of a marked genetic gain

Impact of forest fire on occurrence of Heterobasidion annosum s.s. root rot and other wood-inhabiting fungi in roots of Pinus mugo

Forest fires result in disturbance of wood- and soil-inhabiting fungal communities and also have an impact on the persistence of rot-causing fungi that are present in infected root systems. The aims of the present study were to (1) investigate the occurrence of the root pathogens Heterobasidion and Armillaria in root disease centres on burned and non-burned sites in Pinus mugo forest and (2) study the impact of forest fire on the community structure of other wood-inhabiting fungi colonizing tree roots. A total of 18 root disease centres were investigated in 120-year-old plantations on sandy dunes in the Curonian Spit of western Lithuania, 14 of which were located on burned and 4 on non-burned sites. A total of 484 fungal isolates representing 16 taxa were obtained from 270 P. mugo root systems sampled at 10–30 cm in the soil. The two most frequently isolated fungi were Trichoderma viride and Penicillium sp. found in all disease centres and 96.7 per cent and 39.6 per cent of root systems, respectively. Heterobasidion annosum s.s. was the most commonly isolated basidiomycete found in 15 disease centres. Overall, it was isolated from 19.3 per cent of the root systems. The fungus gave growth from 42.5 per cent of root systems on non-burned and from 15.2 per cent of root systems on burned sites, and the difference was statistically significant (chi-squared test; P < 0.001); thus forest fire in disease centres seemingly had reduced occurrence of the pathogen. Nevertheless, H. annosum s.s. persisted on 11 burned sites, and on four of those fresh sporocarps were observed. Armillaria borealis was less commonly isolated (3.0–5.0 per cent of the root systems)Vytauto Didžiojo universitetasŽemės ūkio akademij

Response of juvenile progeny of seven forest tree species and their populations to simulated climate change-related stressors, heat, elevated humidity and drought

The study aimed to evaluate response and phenotypic plasticity of juvenile progeny of seven forest tree species Pinus sylvestris, Picea abies, Quercus robur, Fraxinus excelsior, Alnus glutinosa, Betula pendula and Populus tremula and their populations to climate change-related stressors, simulated in a phytotron - heat and elevated humidity and heat and drought - in comparison to performance in ambient (control) conditions. Treatment effect on sapling morphometric, physiological and biochemical traits was significant except for health condition, transpiration and photosynthetic rates and water use efficiency (WUE). Species effect and species-by-treatment interaction were strongly significant in most traits studied, indicating a great inter-specific variability of responses to the applied treatments. Compared to control, stem diameter increment was lower for most species following both hot-wet and hot-dry treatments, while treatment impact on height increment was less pronounced and sometimes even positive. Drought caused significant defoliation in P. tremula, A. glutinosa and B. pendula, while under hot-wet treatment the defoliation in most species was lower than in control. Following hot dry treatment, WUE in P. abies, P. sylvestris and B. pendula was lower than following both hot-wet treatment and control, while in P. tremula, A. glutinosa and Q. robur WUE was higher. This suggests that the latter species are able to maintain a balance between photosynthesis and transpiration. Photosynthetic rate was highest in P. tremula, B. pendula and A. glutinosa, however it was much more negatively affected by water deficit in these three species than in other tested species. In most cases, drought had a negative effect on production of pigments in deciduous tree species, which, together with increased amounts of malondialdehyde and hydrogen peroxide, indicated a presence of an oxidative stress. Significant population effect and population-by-treatment interactions found for most traits showed different plasticity and response of tree populations to the treatments. Although, only 19% of the populations showed significant ecovalencies. Some of the observed reactions may not be considered as adaptive acclimation as decreasing growth of some species and populations indicates deteriorating performance which may lead to changes in their competitiveness, thus compromising regeneration, persistence of natural successions and sustainability of forest ecosystems

Biogeographical patterns and determinants of invasion by forest pathogens in Europe

A large database of invasive forest pathogens (IFPs) was developed to investigate the patterns and determinants of invasion in Europe. Detailed taxonomic and biological information on the invasive species was combined with country-specific data on land use, climate, and the time since invasion to identify the determinants of invasiveness, and to differentiate the class of environments which share territorial and climate features associated with a susceptibility to invasion. IFPs increased exponentially in the last four decades. Until 1919, IFPs already present moved across Europe. Then, new IFPs were introduced mainly from North America, and recently from Asia. Hybrid pathogens also appeared. Countries with a wider range of environments, higher human impact or international trade hosted more IFPs. Rainfall influenced the diffusion rates. Environmental conditions of the new and original ranges and systematic and ecological attributes affected invasiveness. Further spread of established IFPs is expected in countries that have experienced commercial isolation in the recent past. Densely populated countries with high environmental diversity may be the weakest links in attempts to prevent new arrivals. Tight coordination of actions against new arrivals is needed. Eradication seems impossible, and prevention seems the only reliable measure, although this will be difficult in the face of global mobility