Siegfried Fink

DETECTION OF DECAY IN TREES WITH STRESS WAVES AND INTERPRETATION OF ACOUSTIC TOMOGRAMS

Summary Cross-sectional maps of stems of beech, Horse chesnut and Norway maple affected by Ganoderma adspersum (Schulz) Donk, Pleurotus ostreatus (Jaquin: Fr.) Kumm and Kretzschmaria deusta (Hoffm.: P. Martin) (=Ustulina deusta (Fr.) Petrak), respectively showing fungal decay were obtained from living trees. Zones of altered fresh- and dry- matter density were constructed, and these compared with Picus® acoustic tomograms of the same cross-sections. The studies shown demonstrate that within a sample cross-section, a zone of decay can be determined accurately for its size and moderately accurately for its position. The shape of the sample cross section influences the accuracy of the acoustic tomograms. Thus the greater the deviation from a circular outline, the poorer the accuracy. Likewise, the number of sensors naturally affects the accuracy. Wood decay caused by Kretzschmaria deusta can be detected by the Picus® acoustic tomograph. The resolution of the tomograms is still worthy of improvement as reaction zones cannot yet be represented, despite their high density. Although capable of improvement in some respects, the Picus® acoustic tomograph currently offers a very good diagnostic support for evaluating the condition of trees and hence their resistance to fracture.

Dual modes of degradation by Fistulina hepatica in xylem cell walls of Quercus robur.

Sequential effects of colonisation by the wood decaying Fistulina hepatica were examined microscopically in naturally infected and artificially inoculated heartwood of pedunculate oak (Quercus robur). For 6 mo, the deposition of brown materials within parenchyma cells containing hyphae was the only visible effect of colonisation. After 12 mo degradation occurred but was initially confined to parenchyma of xylem rays, in which the secondary cell walls showed helically orientated internal cavities containing hyphae, as in a soft rot. The hyphae were covered with a resinous material and persisted in a herringbone pattern after the secondary walls became heavily degraded. The adjacent libriform wood fibres also showed cavity formation. By contrast fibre-tracheids were mainly affected by a brown rot. uv-microscopy indicated that cell types in which the soft rot mode occurred were rich in syringyl lignin, whereas the brown rot was associated with cells rich in guaiacyl lignin. Thus, the present study shows that F. hepatica possesses dual modes of degradation which appear to correlate with the different lignin composition within cell types of oak.

Latent infections of Fomes fomentarius in the xylem of European beech (Fagus sylvatica)

Fungal colonisation originating from endophytic thalli in wood of healthy European beech trees (Fagus sylvatica) was studied. Fungi were isolated from wood immediately after felling and after incubation for 8, 16 and 24 weeks under two different drying regimes. Two media were used to isolate fungi: malt extract agar with and without thiabendazol. Thiabendazol was added to inhibit non-basidiomycetes. The two drying regimes had no influence on the species composition of the recovered mycobiota and the frequency of isolation of these species. Mycelia of basidiomycetes except Coniophora puteana emerged only from wood samples inoculated onto malt extract agar containing thiabendazol. Only a few isolates were obtained from freshly cut wood, but a great number of isolates was recovered already after eight weeks of wood incubation. Four taxa accounted for 88 % of the total number of isolates: Hypoxylon fragiforme, Trichoderma spp., and the basidio-mycetes Coniophora puteana and Fomes fomentarius. The latter had not been considered an endophyte before. The isolates of F. fomentarius were made exclusively from the stem and some large diameter branches, which are the locations of its basidiocarps on dying trees. Every isolate of F. fomentarius was genetically different as revealed by tests for somatic compatibility. Advantages of the presumed endophytic strategy of F. fomentarius are discussed. Microscopic investigations showed a great number of hyphae within the cell lumina of vessels and a distinct wood degradation already after eight weeks of wood incubation.

AN OVERVIEW OF WOOD DEGRADATION PATTERNS AND THEIR IMPLICATIONS FOR TREE HAZARD ASSESSMENT

Summary The identification of decay fungi in tree hazard assessments is of little value unless information about the likely mechanical effects of the decay can thereby be gained. To this end, knowledge of the broad category of decay caused by the fungus concerned brown-rot, white-rotor soft-rot, is useful but generally insufficient, since the mechanical effects within each category may vary greatly. High resolution light microscopy, combined with strength tests, can provide useful details of the wood degradation patterns that occur in a given host/fungus combinations. Studies of several such combinations have shown the biomechanical importance of the preferential degradation of particular zones within the woody structure in the earlier stages of decay. In this context, the ability of certain white-rot fungi such as Inonotus hispidus to switch between different modes of degradation, including soft-rot in some cases, is of considerable significance. These new data help to explain previous, anecdotal observa...

Interfertile oaks in an island environment: I. High nuclear genetic differentiation and high degree of chloroplast DNA sharing between Q. alnifolia and Q. coccifera in Cyprus. A multipopulation study

The evergreen Quercus alnifolia and Q. coccifera form the only interfertile pair of oak species growing in Cyprus. Hybridization between the two species has already been observed and studied morphologically. However, little evidence exists about the extent of genetic introgression. In the present study, we aimed to study the effects of introgressive hybridization mutually on both chloroplast and nuclear genomes. We sampled both pure and mixed populations of Q. alnifolia and Q. coccifera from several locations across their distribution area in Cyprus. We analyzed the genetic variation within and between species by conducting analysis of molecular variance (AMOVA) based on nuclear microsatellites. Population genetic structure and levels of admixture were studied by means of a Bayesian analysis (STRUCTURE simulation analysis). Chloroplast DNA microsatellites were used for a spatial analysis of genetic barriers. The main part of the nuclear genetic variation was explained by partition into species groups. High interspecific differentiation and low admixture of nuclear genomes, both in pure and mixed populations, support limited genetic introgression between Q. alnifolia and Q. coccifera in Cyprus. On the contrary, chloroplast DNA haplotypes were shared between the species and were locally structured suggesting cytoplasmic introgression. Occasional hybridization events followed by backcrossings with both parental species might lead to this pattern of genetic differentiation.

IN VITRO SCREENING OF AN ANTAGONISTIC TRICHODERMA STRAIN AGAINST WOOD DECAY FUNGI

The objective of the in vitro studies was to identify a Trichoderma strain with a high antagonistic potential against the basidiomycetes Ganoderma adspersum, Ganoderma lipsiense, Inonotus hispidus, Polyporus squamosus and the ascomycete Kretzschmaria deusta. For this purpose dual culture and interaction tests in wood blocks as well as investigations on fungal growth and germination behavior of conidia under different conditions were performed. Hyphal interactions were observed by scanning electron microscopy (SEM). The effect of Trichoderma spp. on wood colonization and degradation of wood decay fungi were quantitatively analyzed by means of dry weight loss measurements of wood and qualitatively by histological studies. The different Trichoderma species all showed an antagonistic potential against wood decay fungi in the in vitro studies. However, significant differences between the species and strains were found (P<0.001). Trichoderma atroviride (T-15603.1) showed the highest competitive activity against most wood decay fungi. An influence of physical and chemical parameters, in particular temperature and water potential on growth and germination behavior of conidia was evident. The species of wood decay fungi showed significant differences in their sensitivity when challenged by Trichoderma. Polyporus squamosus showed an extensive resistance in most laboratory tests indicating that target specificity of the antagonist needs consideration.

Resistance of parenchyma cells in wood to degradation by brown rot fungi

Wood degradation by two basidiomycetes, Fomitopsis pinicola and Laetiporus sulphureus was studied in one conifer and four broadleaved trees: Picea abies (Norway spruce), Acer pseudoplatanus (sycamore), Betula pendula (birch), Quercus robur (common oak) and Robinia pseudoacacia (robinia). Observations of birefringence under polarized light showed that in all hosts both brown rot fungi affected cells of the early wood before those of the late wood. Degradation of cellulose, as shown by the loss of birefringence, was apparent after 6 weeks in the cell wall of fibres and fibre tracheids, but even after 12 weeks, axial parenchyma showed no signs of degradation. The results indicate that both brown rot fungi cause higher weight losses in hosts (P. abies and B. pendula) with a small amount of parenchyma cells, whereas the lowest weight losses are associated with wood containing a high amount of parenchyma cells (Q. robur and R. pseudoacacia). Resistance of parenchyma cells to degradation by brown rot fungi appears to be related to the cell wall morphology of parenchyma cells and may also reflect a low co-evolutionary adaptation of brown rot fungi to the xylem of broadleaved trees.

Interfertile oaks in an island environment. II. Limited hybridization between Quercus alnifolia Poech and Q. coccifera L. in a mixed stand

Hybridization and introgression between Quercus alnifolia Poech and Q. coccifera L. is studied by analyzing morphological traits, nuclear and chloroplast DNA markers. The study site is a mixed stand on Troodos Mountains (Cyprus), and the analyzed material includes both adult trees and progenies of specific mother trees. Multivariate analysis of morphological traits shows that the two species can be well distinguished using simple leaf morphometric parameters. A lower genetic diversity in Q. alnifolia than in Q. coccifera and a high interspecific differentiation between the two species are supported by an analysis of nuclear and chloroplast microsatellites. The intermediacy of the four designated hybrids is verified by both leaf morphometric and genetic data. Analysis of progeny arrays provides evidence that interspecific crossings are rare. This finding is further supported by limited introgression of chloroplast genomes. Reproductive barriers (e.g. asynchronous phenology, postzygotic incompatibilities) might account for this result. A directionality of interspecific gene flow is indicated by a genetic assignment analysis of effective pollen clouds with Q. alnifolia acting as pollen donor. Differences in flowering phenology and species distribution in the stand may have influenced the direction of gene flow and the genetic differentiation among effective pollen clouds of different mother trees within species.

Resistance of fibre regions in wood of Acer pseudoplatanus degraded by Armillaria mellea

The white rotting Armillaria mellea induced a spatially very distinctive pattern of degradation in sycamore wood, under both natural and artificial conditions. Degradation began preferentially within groups of fibres containing intercellular spaces, whereas fibre regions lacking such spaces were undegraded and remained largely intact even when decay had become advanced elsewhere. The two types of fibre region differed not only in the presence of intercellular spaces, and hence in the potential for gas exchange, but also in their degree of lignification. This was higher in the more resistant type, as shown by staining of undecayed wood with toluidine blue-O, by microspectrometry after staining for the Maule colour reaction, and by uv-microscopy. A spatially similar pattern of cellulose degradation was induced by the brown rotting Laetiporus sulphureus, which is known to cause preferential degradation of less strongly lignified cell walls. By contrast, the white-rotting Ganoderma pfeifferi showed a tendency to degrade the stronger lignified cell walls. Thus, in combination with the application of conventional histological methods, the wood degradation modes observed give additional evidence for stronger and weaker lignified fibre regions within the wood of sycamore.

FIELD EXPERIMENTS TO EVALUATE THE APPLICATION OF TRICHODERMA STRAIN (T-15603.1) FOR BIOLOGICAL CONTROL OF WOOD DECAY FUNGI IN TREES

Field experiments were carried out at different locations and on hosts with T-15603.1, a Trichoderma strain for biological control of wood decay fungi. The objective of the studies was to monitor and optimize conditions for colonization of the antagonist, its survival in time and space and to improve its effectiveness as wound treatment method. A total of 159 angiosperm trees and 1431 wounds from six different species (Platanus x hispanica, Acer pseudoplatanus, Tilia platyphyllos, Populus nigra, Quercus rubra, Robinia pseudoacacia) were treated with different conidial suspensions of T-15603 .1. In comparison to untreated control wounds, T-15603 .I significantly suppressed growth (82.3%) of wounds colonised by three basidiomycetes Ganoderma adspersum, lnonotus hispidus and Polyporus squamosus (P<O.OOI ). Monitoring results with RAPD-PCR showed that spore suspensions applied in a humidity storing gel as a carrier suspension significantly increased the germination rate and therefore colonization of the wound surface by T-15603.1 (P<O.OO I). Interpretation and characterization of the isolated microorganisms such as diversity and succession were analyzed using diversity indices. The results demonstrate that T-15603.1 can be successfully applied as a biological wound treatment against wood decay fungi of urban trees.