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.
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.
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.
Key message Fungal infection was outlined as a potential reason for the onset of indented annual growth ring formation during the juvenile phase of hazel wood growth. Annual growth ring indentations resulted from the formation of disturbed zones which originated solely in close proximity to leaf traces. Context Hazel wood is an abnormal type of woody tissue that is formed as a result of exogenous stimuli that may trigger long-term responses in the cambium. Cambial responses produce anatomical alterations in the surrounding xylem tissue that can be observed as an indentation of annual growth rings. The chemical profiles of lignan hydroxymatairesinol may provide an indication of its possible role in the protection of a living tree against the spread of a fungal or microbial infection at the onset of indentation. Aims The objectives of this study were to reveal the anatomical differences in the altered woody tissue of Picea abies hazel wood at both the onset and the later stages of annual growth ring indentation and to determine the chemical profiles for hydroxymatairesinol upon elicitation by a fungal infection in the disturbed zones. Methods Light and scanning electron microscopy observations were carried out on radial, tangential, and cross sections of hazel wood zones separated from P. abies stems. Concentrations of hydroxymatairesinol were determined for both the disturbed zones and the non-indented zones using a gradient high-performance liquid chromatography. Results The formation of disturbed zones was accompanied by significant changes in both the direction and width of the tracheids which produced an abnormal formation of intertwined and twisted tracheids. Fungal hyphae, radial cell wall cracks, and unusually large cross-field pitting were all found in the tracheids of the disturbed zones. Conclusion The content of hydroxymatairesinol in the acetone extract determined from the disturbed zones was 3.4 times greater than that present in the non-disturbed tissues. By means of vascular dysfunction in the leaf traces, host trees responded to the fungal infection by plugging the lumens of conductive leaf trace tissue and filling the vascular pathway with polyphenolic compound deposits.
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.
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