Kretzschmaria Deusta Research Articles

Interactions between callus cultures of European beech, indigenous ascomycetes and derived fungal extracts.

Ascomycete fungi from the Xylariaceae and Diatrypaceae responded in three distinct ways when grown in dual culture with callus material of beech (Fagus sylvatica L.). Growth of the putative weak pathogens Biscogniauxia nummularia (Bull.) O. Kuntze and Eutypa spinosa (Pers.) Tul. & C. Tul. was stimulated whilst the saprotrophs Ustulina deusta (Hoffm.) Lind. and Xylaria polymorpha (Pers.) Grev. were unaffected by the presence of callus. Sapwood-colonizing fungi displayed a range of responses, with Diatrype stigma (Hoffm.) Fr. being unaffected, Diatrype disciformis (Hoffm.) Fr. stimulated, and Hypoxylon fragiforme (Pers.: Fr.) Kickx and 'Hypoxylon purpureum' inhibited by the presence of callus. Changes in morphology were evident in many of the fungi during interactions, with yeast-like forms being produced by those members of the Xylariaceae which have been recognized as endophytes. Reciprocally, high concentrations of cell free extracts of some of the Xylariaceous fungi resulted in necrosis or inhibition of callus growth, while at sub-lethal concentrations marked stimulation of growth was evident. The importance of these results with respect to pathogenicity testing and elucidation of the biology of tree-fungus interactions is discussed.

Reaction zone relics and the dynamics of fungal spread in the xylem of woody angiosperms

Relics of reaction zones, typical of those found at the margin between fungally colonized and healthy sapwood, have been identified in the decayed xylem of three woody angiosperms. In Aesculus hippocastanum L., decayed by Ustulina deusta (Fr.) Petrak the locations of these relics were indicated both by residual traces of the characteristic induced compounds that accumulate in reaction zones, and by the dark pseudosclerotial plates that are formed by this fungus at reaction zone margins. In Fagus sylvatica L., decayed by a Ganoderma sp., the sites of former reaction zone margins were marked by bands of wood in which a high proportion of the vessels had suberized linings or occluding tyloses. In Fraxinus excelsior L., decayed by Inonotus hispidus Bull. ex Fr.) P. Karst., the sites of reaction zones were indicated by the presence of brown, insoluble, deposits in the cells and vessels of the xylem. In all cases these relics formed narrow, clearly defined bands, typically separated from neighbouring reaction zones (functional or otherwise) by intervening decayed regions largely devoid of characteristic reaction zone features. These results, obtained from three species all somewhat different in the nature of their reaction zone responses, indicate that the invasion of functional xylem tissues by decay-causing pathogens in these trees is discontinuous. Reaction zones form persistent static boundaries to the lesion. When these fail the invasion of previously uncolonized sapwood tissues may be rapid, and is accompanied by little or no dynamic expression of defence or repair responses ahead of the infection front. Ultimately this invasive phase ends, and locally at least, the lesion becomes bounded by a fully developed reaction zone once again. The mechanisms that may limit fungal colonization of these host tissues are discussed.

Fossil ascopores of the parasitic fungus Ustulina deusta in Eemian deposits in Denmark

Records of spores of the parasitic ascomycete Ustulina deusta were compared with the pollen records of potential host trees in Eemian deposits. The results indicate that the distance between sample site and forest has a considerable influence on the frequency records of the fungal spores. Spores are absent in deposits from the relatively large lakes at Hollerup and Herning. The deposit in a small (5 × 5m) hollow at Egernsund shows high frequencies of Ustulina in the vegetational phase 3 ( Fraxinus phase). In phase 4a, dominated by Corylus, the spores of Ustulina were almost absent, whereas phase 4b, dominated by Tilia, shows extremely high frequencies of the ascospores. The relationship between the fungus and its arboreal hosts at Egernsund ( Tilia, Fraxinus) reflects the weak parasitic character of the fungus. Corylus apparently was not infected, which is in agreement with its absence in the records of host plants of Ustulina deusta in the mycological literature.

An Upper Eemian lake deposit from Twente, eastern Netherlands

Study of micro- and macrofossils from a c. 80 cm thick organic deposit at Kamphuis (Twente, eastern Netherlands) provided information about vegetational succession in a lake and the surrounding marsh and forest. The deposit lies at the base of more than 20 m of predominantly sandy Weichselian sediments. The pollen diagram indicates an Upper Eemian (last Interglacial) age: zones E4b, E5 and E6a. The most abundant dry forest pollen types of zone E4b are Corylus, Taxus and Quercus. Zone E5 is mainly characterized by a rise of the pollen curves of Carpinus and Picea and zone E6 shows a pronounced maximum of Picea. The recorded changes in forest composition may have been related to soil development, but there are no palaeoecological indications of an acidification concomitant with the final dominance of Picea. The presence of Ilex and Hedera pollen in zone E6a possibly indicates that this Picea dominance was not related to a decline in mean temperature. The expansion of the midly parasitic fungus Ustulina deusta is apparently related to increasingly unfavourable conditions for the growth of deciduous forest elements. Macrofossils of local aquatic plants, marsh plants and invertebrates indicate a stagnant, eutrophic and base-rich aquatic environment. Some unknown and not generally known micro- and macrofossils are described and illustrated.