When monitoring the state of health of Fraxinus excelsior trees, unusual symptoms were discovered within a F. excelsior plantation in Bosnia and Herzegovina. These symptoms included the appearance of necrosis and cankers in the basal parts of the trees, followed by the formation of fruiting bodies, however, none of these symptoms were found in the crowns. After sampling and isolation of the necrotic parts from the stem base, pathogen Neonectria punicea was isolated and identified from the characteristics of pure cultures, morphology of the fruiting bodies, and from multilocus sequencing. In field conditions, juvenile F. excelsior trees were inoculated with two N. punicea isolates obtained from the necrotic tissues of both juvenile F. excelsior and mature Fagus sylvatica trees. In both isolates, 12 months post inoculation, the lengths and widths of the necroses were significantly larger compared to the control. Necroses of significantly larger lengths, widths and surfaces were found again in both tested isolates 24 months post inoculation. In the case of the F. excelsior isolate, the lengths of the necroses at both the stem base and at breast height increased by 1.6 times, whereas the F. sylvatica isolate increased in size by up to 1.7 and 1.8 times, respectively. Trees inoculated without a previous bark wound showed no symptoms, similar to the control trees. Scanning electron microscopy and X-ray micro-computed tomography imaging revealed that N. punicea hyphae penetrated from the cankers to the woody outermost annual growth ring and that hyphae were present mostly in the large earlywood vessels and rarely in the axial parenchyma cells. Hyphae also spread radially through the pits in vessels. The infected trees responded with the formation of tyloses in the vessels to prevent a rapid fungal spread through the axial vascular transport pathway. The ability of N. punicea to cause necroses in juvenile ash trees was demonstrated for the first time during this study. It poses a serious threat to planted forests and natural regenerations of F. excelsior especially if F. sylvatica is considered as a possible inoculum reservoir for future infections. This pathogen should be integrated within future ash resistance or breeding programs.

Phytophthora infections are followed by histological alterations, physiological and metabolomic adjustments in the host but very few studies contemplate these changes simultaneously. Fagus sylvatica seedlings were inoculated with A1 and A2 mating types of the heterothallic P. ×cambivora and with the homothallic P. plurivora to identify plant physiological and metabolomic changes accompanying microscope observations of the colonization process one, two and three weeks after inoculation. Phytophthora plurivora-infected plants died at a faster pace than those inoculated with P. ×cambivora and showed higher mortality than P. ×cambivora A1-infected plants. Phytophthora ×cambivora A1 and A2 caused similar progression and total rate of mortality. Most differences in the physiological parameters between inoculated and non-inoculated plants were detected two weeks after inoculation. Alterations in primary and secondary metabolites in roots and leaves were demonstrated for all the inoculated plants two and three weeks after inoculation. The results indicate that P. plurivora is more aggressive to Fagus sylvatica seedlings than both mating types of P. ×cambivora while P. ×cambivora A1 showed a slower infection mode than P. ×cambivora A2 and led to minor plant metabolomic adjustments.

The role of Ophiostoma quercus in oak decline, a significant threat to European oak ecosystems, has been debated for nearly a century. This long-term field experiment assessed the aggressiveness of O. quercus on Quercus petraea and monitored both fungal spread and tree defense responses, combining pathology, microscopy, X-ray tomography, FTIR, HPLC and proteome analyses. Fifty-nine months post-inoculation, 30 % of trees exhibited decline symptoms, while 70 % displayed extensive cankers and lesions, 28.3 times larger than those on controls. Infected trees responded by forming tyloses, blocking water transport around the inoculation site. Following infection, increased deposition of polyphenolic compounds was observed in both barrier and reaction zones. Histopathological observations and FTIR measurements revealed enhanced local deposition of suberin, lignin, lignin-related compounds, and tannins within the lumens of ray parenchyma cells, and the cell walls of both libriform fibers and vessels. Proteomic analyses suggest that host trees are employing a salicylic acid-based defense strategy. At the tissue level, these analyses indicate a shift in metabolic pathways, with downregulation of lignin biosynthesis and upregulation of flavonoid and stilbenoid biosynthesis, as evidenced by increased chalcone synthase abundance. Our groundbreaking use of submicron-computed X-ray tomography on woody tissues could pave the way for the widespread adoption of non-destructive 3D scanning technology in plant-fungal interaction research. The findings of this study demonstrated the aggressiveness of O. quercus towards adult Q. petraea and its contribution to the widespread syndrome of oak decline.

The morphology of cellular elements of juvenile wood of spruce has, in comparing to mature wood, different parameters. Subsequently, indented growth ring zones, caused by genetic predisposition and cambial injury, can significantly change the morphology of these tissues. The aim of the paper compared the morphology of cellular elements of juvenile wood originating in the indented and the normal growth rings. The results confirmed a significant difference in the proportion, the dimensions and shape of parenchyma cells and tracheids. While, in zones containing the indented growth rings the proportions were 15.6 % and 84.4 %, in normal growth rings were 10.4 % and 89.6 %. Tracheids in the indented growth ring zones were shorter and narrower (1.47 mm and 25.4 µm), but in normal growth ring zones longer and wider (2.14 mm and 28.3 µm). Tracheids from marginal and central zones normal growth rings showed considerable inhomogeneity in longitudinal shape (they were twisted). On the basis of change tissue morphology in the juvenile growth phase we can expect the impact of these growth disproportions on the quality production of pulp and paper, mainly in assortments with small diameter.

This short review summarises the history and current knowledge regarding beech bark disease (BBD) in Slovakia. Moreover, the results of ongoing long-term disease monitoring are summarised. The article also provides a list of the 29 Nectria s.l. species found to date in Slovakia, complete with information about their occurrence on host tree species. Above all, we highlight the need for histopathological research on beech tissues attacked by different Nectria spp. Notably, neither the defensive response mechanisms of host cellular tissues at the anatomical and biochemical levels nor the strategy of decomposition by different pathogens have been explored in beech.

Injuries to standing trees caused by logging and the subsequent changes in biochemical composition and anatomy of affected tissues lead to wood quality loss, thus lowering the commercial value of roundwood. In this study, we investigated the influence of various factors that could help mitigate or prevent the spread of infections in the stem caused by injuries. A total of 112 beech logs (tree age: 42-143 years) from ten forest stands at three different sites in central Slovakia were examined, and the extent of discolouration and decay zones in each stem was measured, along with cambial age, stem diameter, injury width, and injury closure period. The results showed that the width of physiologically active wet sapwood and the width of the inactive dehydrated zone in the stem are important factors influencing red heartwood formation. We found no significant differences in the extent of discolouration and decay among different stands and sites. Stem diameter and injury width did significantly affect the penetration of infection through sapwood, and red heartwood formation was significantly affected by cambial age and injury width, while stand age, site slope, beech proportion in the stand and injury closure did not show any significant effect. Binary logistic models were applied to assess the probability of pathogen penetration through sapwood into the stem dehydrated zone as a function of injury width and stem diameter, as well as the probability that this could lead to red heartwood formation based on injury width and cambial age of beech stems.