Arboriculture & Urban Forestry 33(6): November 2007 411 species, infrequent species were included in the key either as important tree pathogens or as aggressive decay agents on standing trees (Strouts and Winter 1994; Lonsdale 1999; Nicolotti 2004b). Selection of Characters and Key Construction Only characters resulting from macroscopic observations of the basidiomata, of their longitudinally cross-sections, or of the color of spore print were retained as good characters for taxa discrimination in this work. Selected characters were: the absence or the presence and the point of insertion (i.e., lateral, central) of the stalk; the general shape of the basidi- omata (i.e., resupinate, applanate, ungulate, and so on); the type of hymenophore (i.e., smooth, lamellate, with pores); the color of the hymenophore and its reaction when bruised; pore shape and size; the color, the consistency, and the general features of the sterile surface, including the presence of hairs or other appendages and its reaction to fire exposure; the color and the odor of the context, and the presence of differ- ently colored lines or layers within the context as assessed through observations of longitudinally cross-sections of the basidiomata; and the color of the spore print. All these characters were used to describe each of the previously selected wood-rotting basidiomycetes. Data col- lection was performed by comparing the descriptions of de- cay fungi available from the literature (Breitenbach and Kränzlin 1986; Breitenbach 1991, 1995; Lonsdale 1999; In- tini et al. 2000; Bernicchia 2005) and by accurate observa- tions of fresh specimens of the Herbarium of the Department of Exploitation and Protection of the Agricultural and For- estry Resources–University of Torino (Torino, Italy), previ- ously identified with the aid of analytical keys (Breitenbach and Kränzlin 1986; Breitenbach 1991, 1995, 2005). Key Validation Basidiomata were identified in the field with the aid of the key included in the present paper singly by eight MSc stu- dents of Forestry and Environmental Sciences (University of Torino). After field identification, basidiomata were col- lected, transferred to the laboratory, and determined with ana- lytical keys by mycologists as described previously. The validation of the key was assumed to be accomplished if the number of basidiomata successfully identified with the field key on the total number of basidiomata collected, over- all and for each taxon, was over 0.7 (validation cutoff ratio). RESULTS Sixty-four fungal taxa were included in the key (Appendix). Taxa, which are listed in Table 1, belonged to the following families: Bolbitiaceae, Bondarzewiaceae, Coniophoraceae, Fistulinaceae, Fomitopsidaceae, Ganodermataceae, Gloeophyl- laceae, Hapalopilaceae, Hymenochaetaceae, Marasmiaceae, Meripilaceae, Meruliaceae, Pleurotaceae, Polyporaceae, Schizo- phyllaceae, Stereaceae, and Strophariaceae. The key was built to determine wood-rotting basidiomy- cetes at the species level. Armillaria mellea complex and Heterobasidion annosum complex represent two exceptions and are referred in the key as Armillaria spp. and Heteroba- sidion spp., respectively. Basidiomata collected and identified in the laboratory for key validation belonged to 55 of the 64 taxa included in the field key. Two to three basidiomata were found for each fungal taxon, resulting in a total of 992 case studies (124 basidiomata × eight identifiers). Overall, the determination with the field identification key matched that obtained with the analytical key in 893 case studies (validation ratio 0.900). With the exception of Ganoderma adspersum, all the taxa resulted in validation ratios higher or equal to 0.750 (Table 1). DISCUSSION The most common wood-rotting species of basidiomycetes occurring on standing trees in central and southern Europe were considered for key construction, irrespective of their ecological behavior. In addition to strict saprobes, the species list includes root pathogens (e.g., Armillaria spp., Heteroba- sidion spp., Inonotus dryadeus, Ganoderma adspersum), stem pathogens (e.g., Chondrostereum purpureum, Phellinus pini, Inonotus hispidus), and fungi associated with the root system or the bole and known for their negative interactions with the tree stability either in the forest (i.e., Climacocystis borealis) (Rigling et al. 2005) or in urban landscape (i.e., Perenniporia fraxinea) (Nicolotti 2004b). Taxonomic keys are generally built to discriminate taxa within systematic groups. This is true also for wood decay fungi. Keys to Corticiaceae s.l. (Hjortstam et al. 1978), Polyporaceae s.l. (Bernicchia 2005), and even Aphyllopho- rales (Breitenbach and Kränzlin 1986), although very analyti- cal, fail to some extent in that, in each of them, one or more groups of decay fungi are lacking, and consequently, none can be used as a unique tool for the identification of decay fungi occurring in standing trees. Members of 17 families of all the four orders of wood decay basidiomycetes, including Agaricales, are considered in our field key. In general terms, this represents a great advantage with respect to other pub- lished keys, because it would allow the determination to non- mycologists that could ignore the differences of basidiomata at the family level, which is rarely reported in traditional keys. The key is validated, because the ratio of basidiomata suc- cessfully identified on the total number of basidiomata in- cluded in the validation process was greatly higher than the adopted validation cutoff ratio. Ganoderma adspersum was characterized by the lowest validation ratio (0.708) and was mostly confused with G. applanatum. Very low divergences ©2007 International Society of Arboriculture
November 2007
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