Armillaria in the Northern 

 Rockies: Delineation of 

 Isolates Into Clones 



Geral I. McDonald 

 Neil E. Martin 



INTRODUCTION 



Soil-inhabiting fungi belonging to the genus Armillaria 

 cause root disease and decay on most woody plant species 

 throughout the world (Wargo and Shaw 1985). Recent 

 findings have contributed to an understanding of the tax- 

 onomy (Korhonen 1978; Morrison and others 1985; Ullrich 

 and Anderson 1978), physiologic interaction (Wargo 1984), 

 and ecological relationships (McDonald and others 1987) of 

 the genus. 



Knowledge about distribution and behavior of Armil- 

 laria spp. in several regions has appeared in recent years. 

 Two reports published in 1978 outlined the concept of 

 intersterility groups and mapping of the geographic extent 

 of clones. One dealt with the genus in the northeastern 

 portion of North America (Ullrich and Anderson 1978) and 

 the other with Armillaria in Finland (Korhonen 1978). 

 The above authors outlined necessary technology to map 

 the extent of both vegetative and sexually active clones. 

 Isolates will fail to join together because they belong to 

 different intersterility groups or they are different 

 genotypes within the same group. 



These reports, together with more recent information, 

 supply technology necessary to tentatively identify the tax- 

 onomic affiliation of vegetatively delineated clones, pro- 

 vided that fresh basidiospores of all species represented in 

 the vegetative population are available. Six intersterile 

 groups have been identified in Europe. Their taxonomic 

 affinities were demonstrated using these techniques. The 

 groups are as follows: Korhonen's (1978) group D = 

 Armillaria mellea (Vahl:Fr.) Kummer, group A = A. 

 borealis Marxmuller et Korhonen, group E = A. bulbosa 

 (Barla) Watling, group B = A. cepistipes Velenosvsky, and 

 group C =^ A. ostoyae (Romagnesi) Herink (Roll-Hansen 

 1985). 



Ten intersterility groups were found in North America 

 (Anderson and Ullrich 1979). Two of the 10 were later 

 consolidated with two others, which resulted in eight 

 groups (Anderson 1986). In the meantime, an additional 

 intersterile group was proposed (Morrison and others 

 1985). Genetic and taxonomic connections were recently 

 reported among A. mellea (North American group VII) 

 growing in the State of Virginia and Korhonen's group D. 

 In addition these connections were shown between A. 

 bulbosa (North American group VII) grovdng in the State 

 of Maryland and Korhonen's group E (Motta and 

 Korhonen 1986). A definite connection was made between 

 Korhonen's group C {A. ostoyae) and North American 

 group I (Anderson and others 1980; Morrison and others 

 1985). Finally, a tentative connection was shown in 

 Anderson and others' (1980) data between A. bulbosa and 



North American group VII and between A. cepistipes and 

 North American group X. 



These gains in clarifying the identity of Armillaria 

 isolates are significant, but several points of confusion still 

 exist. Most workers (Adams 1974; Kile 1981; Korhonen 

 1978; Shaw and Roth 1976) have limited their studies to 

 rhizomorphic and fan collections from diseased plants or 

 stumps in areas of obvious infection or, if collections 

 covered a wider geographic area, they were limited to 

 fruiting bodies (Anderson and Ullrich 1979; Morrison and 

 others 1985). These sampling philosophies may provide a 

 biased view of Armillaria because all populations do not 

 fruit regularly and because potentially pathogenic popula- 

 tions can exist in a nonfruiting status on apparently 

 healthy hosts. Korhonen (1978) concluded that clonal 

 delineation of isolates in Finland by both vegetative and 

 genetic means gave nearly identical results. In terms of 

 clone size, both methods gave similar results in Western 

 North America (Anderson and others 1979). 



Effective management of forests where Armillaria is a 

 potential threat requires the answers to several basic ques- 

 tions. Is risk uniform over a forested area or does it vary, 

 and can it be predicted by applying certain criteria? Are 

 all hosts at equal risk? If not why not? Do certain forest 

 management actions increase the problem and others 

 reduce it? Answers to these questions require knowledge 

 about the distribution and behavior of the genotypes, 

 ecotypes, and species of the causal organism over a large 

 area. A study was conceived to answer some of these 

 questions as they pertain to an area 600 miles in diameter, 

 centered on Moscow, ID. Because our goal was to char- 

 acterize the Armillaria population over the entire area, 

 initial sampling was limited to vegetative structures. This 

 paper reports the delineation of clones and their geo- 

 graphic and host range from Armillaria isolates sampled 

 as vegetative structures on eighty-seven 0.04-hectare ran- 

 dom plots located on 12 National Forests. 



MATERIALS AND METHODS 



Plot selection, plot location, and fungus isolation pro- 

 cedures were described previously (McDonald and others 

 1987). Contaminant-free isolates (individual pure cultures) 

 of the genus were tested for compatibility without know- 

 ing the identity of the isolates (blind challenge test) in the 

 following fashion: Up to six isolates were inoculated onto 

 3 percent malt extract agar (2 percent agar) in 50-mm 

 plastic culture (petri) plates according to the pattern 

 shown in figure 1. A 1-mm plug of each isolate was cut 

 from the edge of an actively growing colony and placed 5 

 mm from its neighbor. All field isolates were presumed to 



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