Abstract
Hygrophorus olivaceoalbus has long been known as an ectomycorrhizal fungus, formerly designated with the artificial binomen Piceirhiza gelatinosa. Recently, it has been found to be abundant and very frequent under double ambient ozone free air fumigation of mature Norway spruce trees. As it has already been reported that this fungus can form intercellular hyphae within the root meristem, a more detailed study was performed to clarify its type of root colonization. The present study not only revealed intercellular hyphae within the meristematic zone but also intracellular hyphae within root cortex cells which grow towards and into large tannin droplets—phenolic compounds usually deposited as defensive aids—to finally fill them completely. The hyphal assemblages become globular which at first sit as separated hyphal balls within cells still containing cytoplasm. Later on, they are apparently released from the root cells, presumably as microsclerotia for dispersal of the species. Old ectomycorrhizae (ECM) show an apical pore, and later a large orifice of a tube-like cylinder formed by the thick, persistent hyphal mantle. The root tissue is progressively degrading towards proximal parts. Disintegrating root cells apparently liberate the microsclerotia through the orifice. Further studies have to find out the mechanism by which the microsclerotia are liberated and whether they operate as asexual propagules and lastly how and by whom they are propagated. As these ECM are found under ozone stress, and with identical features at higher altitudes, stress impact on trees might be the causative agent for the high frequency and abundance of Hygrophorus olivaceoalbus ECM.
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Acknowledgment
The skilful preparations of the sections by my technicians, Edi Marksteiner and Claudia Bubenzer-Hange, are warmly acknowledged. The help of my PhD student Rita Verma with counting ECM of the Kranzberger Forest plots, calculating absolute frequency and relative abundance and for critically reading the manuscript, and the help of my PhD student Sebastian Gardt for compiling serial sections of the microsclerotia is highly appreciated. Last but not least, I thank Deutsche Forschungsgemeinschaft (DFG) for financial support of our project B7 of SFB 607.
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Agerer, R. Asexual reproduction of Hygrophorus olivaceoalbus by intracellular microsclerotia in root cells of Picea abies – A winner of ozone stress?. Mycol Progress 11, 425–434 (2012). https://doi.org/10.1007/s11557-011-0757-y
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DOI: https://doi.org/10.1007/s11557-011-0757-y