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(American Journal of Botany. 2009;96:1274-1280.) doi: 10.3732/ajb.0800239 © 2009 Botanical Society of America, Inc.

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Pathogenesis of bryophyte hosts by the ascomycete Atradidymella muscivora¹

Department of Biological Sciences, University of Alberta, Edmonton, Alberta, T6G 2E9, Canada

ABSTRACT

Atradidymella muscivora (Pleosporales) is a bryophyte pathogen that infects the mosses Aulacomnium palustre, Hylocomium splendens, and Polytrichum juniperinum. Light and scanning electron microscopy and extracellular enzyme production were used to characterize the interactions between this fungus and its native hosts and the model host Funaria hygrometrica. Penetration was direct via hyphae or appressoria, and hosts responded by forming layered, darkly pigmented deposits at penetration sites, similar to the papillae formed by vascular plants in response to fungal infection. Infected hosts gradually became chlorotic as hyphae grew intracellularly, presumably killing host cells. Pycnidia of the Phoma anamorph (P. muscivora) and uniloculate pseudothecia were initiated as tightly packed masses of stromatic dematiaceous hyphae within a single host cell. Mature pycnidia and pseudothecia were erumpent. A new microniche among bryophilous fungi is described, whereby A. muscivora supplants the gemmae of Aul. palustre and exploits the normal nutrient-flow of the moss gametophyte. Atradidymella muscivora produced both cellulases and soluble polyphenolic oxidases, allowing it to also function as a saprobe and degrade the cell walls of bryophytes. The saprophytic and pathogenic abilities of A. muscivora suggest it may play a role in nutrient cycling, population dynamics, and small-scale disturbances in boreal ecosystems.

Key Words: bryophilous • cell wall degradation • host response • microniche • papilla • pathogenesis • Phoma muscivora • stroma reduction

Received for publication 14 July 2008. Accepted for publication 27 February 2009.

FOOTNOTES

¹ This work was supported by a Natural Sciences and Engineering Research Council of Canada (NSERC) Canadian Graduate Scholarship (CGS) (Master’s level), a NSERC-CGS (Doctoral level), an Alberta Ingenuity Fund (AIF) Incentive Award, and an Alberta Conservation Association (ACA) Grant in Biodiversity to M.L.D. and a NSERC Discovery Grant to R.S.C.

² Author for correspondence (e-mail: marie.davey{at}umb.no); present address: Department of Ecology and Natural Resource Management, Norwegian University of Life Sciences, Postboks 5003, 1432 Ås, Norway; and Molecular Evolution Research Group, Department of Biology, University of Oslo, Postboks 1066 Blindern N-0316 Oslo, Norway

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