426 Journal of Basic Microbiology 2008, 48, 426 – 429 © 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.jbm-journal.com Short Communication Two-dimensional fractal growth properties of the filamentous fungus Cryphonectria parasitica: the effects of hypovirus infection Michael R. Golinski 1, 2 , William J. Boecklen 1 and Angus L. Dawe 1, 3 1 Department of Biology, New Mexico State University, Las Cruces, NM 2 Antiviral Research Center, University of California, San Diego, CA 3 Molecular Biology Program, New Mexico State University, Las Cruces, NM Whole-colony two-dimensional fractal growth patterns produced by hypovirus-infected Cryphonectria parasitica (EP155/CHV1-EP713) were measured and compared with those produced by the isogenic virus-free strain (EP155) on solid medium. We have quantified statistically significant differences in the rates of expansion and spatial dynamics of colony growth be- tween the two strains and concluded that fractal dimension is affected by the presence of the hypovirus. Therefore, fractal dimension measurement is an effective quantitative tool for testing the effects of mycovirus infection on fungal growth parameters. Keywords: Fungal colony growth / Hypovirulence / Mycovirus Received: January 19, 2008; accepted March 27, 2008 DOI 10.1002/jobm.200800017 Introduction * The ability of fungal hyphae to penetrate the growth medium and the interconnected nature of a mycelial colony form that permits translocation of nutrients from one zone of growth to another is a crucial advan- tage in the exploitation of resources [1, 2]. The descrip- tion of a fungal mycelium in terms of its two-dimens- ional fractal properties has been successfully employed using solid medium [3] and can be expanded to model the growth of fungi in liquid culture [4, 5]. Analyses of the geometric structure of the apical zone of laboratory isolates of different species of filamentous fungi sug- gested that change in colony radius over time is associ- ated with the fractal growth of hyphae [6]. These stud- ies further concluded that as the colony radius of the fungus increased, the fractal dimension of hyphae changes, so that the mycelium can optimize space utili- zation and nutrient assimilation [7]. Such studies have been expanded recently to include the modeling of behavior under a variety of nutritional and other envi- ronmental changes [8] with the aim of developing tools Correspondence: Angus L. Dawe, Department of Biology, MSC-3AF, PO Box 30001, New Mexico State University, Las Cruces, NM, 88003 E-mail: dawe@nmsu.edu Phone: (575) 646-4003 Fax: (575) 646-5665 for better prediction of mycelial growth in both natural and industrial applications. The organism used in this study, Cryphonectria para- sitica, is the agent responsible for the near-elimination of the American chestnut, Castanea dentata, from its natural range across the eastern United States. This fungus can be infected by a mycovirus that induces characteristic alterations in phenotype that include reduced virulence, reduced asexual sporulation and changes in colony growth rate (reviewed by [9]). Al- though associated with all major classes of fungi [10], the mycoviruses of the family Hypoviridae that infect the chestnut blight fungus C. parasitica represent the only viral agents for this entire host kingdom for which infectious cDNA clones have been developed [11 – 13]. Changes in colony expansion rate and morphology have been observed in hypovirus-infected mycelium of C. parasitica, but they have only been quantified by sim- ple analytical methods such as radial growth measure- ment and biomass production [14, 15]. Since spatial dynamics relate to fungal mycelium spread and are determined by the rate of colony expansion [16], the goal of this study was to apply a quantitative measure- ment to whole-colony morphological properties of C. parasitica and determine if such a measure is im- pacted by hypovirus infection.