Genotypes of Fraxinus excelsior with different susceptibility to the ash dieback pathogen Hymenoscyphus pseudoalbidus and their response to the phytotoxin viridiol - a metabolomic and microscopic study.

Eight European ash (Fraxinus excelsior) genotypes with different known susceptibility to Hymenoscyphus pseudoalbidus were tested against the phytotoxin viridiol and their response described at the microscopic and metabolomic level. All ash genotypes were sensitive to the toxin and necrosis was detectable after 24h. Among the three viridiol concentrations used in the experiment, the lowest concentration (14.7µM) yielded markedly lower mean damage scores compared to those resulting from seedlings tested at higher dosages. The highest damage scores were associated with the susceptible ash clones S-101, S-106 and S-125, but also with resistant clone R-104. Three resistant clones (R-131, R-121, and R-118) had lower mean damage scores compared to susceptible clones. Wilting of leaves was more common 48h after treatment and more pronounced on seedlings with high damage scores. The resulting lesions generally lacked browning of tissue and displayed only surface disruption of cells in direct contact with the toxin. A delay in symptom development was evident on all five resistant clones tested with the two higher concentrations of viridiol. LC-HRMS and MS/MS analyses of ash seedling extracts suggest several secoiridoid compounds as well as compounds related to abscisic acid (ABA) to be produced in response to viridiol. ABA-cysteine and xanthoxin were found at significantly higher concentrations in susceptible clones compared to resistant clones after treatment with viridiol, suggesting a primary role of ABA in response to stress. The results observed in this study suggest that genetic resistance to H. pseudoalbidus among ash genotypes may be explained, in part, by the varied response to phytotoxins produced by the fungus.

Pyrone and pyridone compounds in the liquid culture of Physisporinus sanguinolentus.

Chromatographic separation of the liquid culture filtrate of the basidiomycete fungus Physisporinus sanguinolentus has yielded three new compounds viz., 2-methyl-4-pyrone, 2-methyl-5,6-dihydro-4-pyrone and the pyridone form of 4-hydroxy-2-methylpyridine, together with the known triacetic acid lactone, the sesquiterpene dialdehyde merulidial and a derivative of merulidial. Their structures were elucidated by spectroscopic analysis and by comparison to literature data and a synthetic sample. One of the compounds, merulidial, was shown to inhibit the germination of spores and the hyphal growth of the wood-rotting basidiomycete Heterobasidion annosum and the saprophytic mould Cladosporium cucumerinum.

Genetic differentiation in Fomitopsis pinicola (Schwarts: Fr.) Karst studied by means of arbitrary primed-PCR.

Genetic variation within and among one Finnish and three Swedish populations of Fomitopsis pinicola (Schwarts: Fr.) Karst. were studied by amplifying DNA from haploid isolates originating from single spore cultures using two arbitrary primers. Analysis offspring from single fruit bodies revealed only three pairs of codominant alleles among 42 variable genetic markers, the remaining 38 segregated independently. Genetic similarity was measured in terms of Euclidean distance. Individuals in the Finnish population tended to form a distinct cluster in the principal component analysis. Variation within and among populations/regions was partitioned by Analysis of Molecular Variance-AMOVA. Within population variation accounted for 91.6% of the total genetic variation. The remaining 7.68% was accounted for by variation between the Finnish population and each of the three Swedish ones. Variation among the Swedish populations accounted for only 0.72% of the total variation. Wright's Fst was 0.17 for all four populations and 0.13 for the three Swedish populations. These relatively low values indicate that there is gene flow among all populations or that they are derived from a common ancestral population. The observed pattern of genetic variation is probably the result of effective spore dispersal and the continuous distribution of this common early successional species.