Biological Species ofArmillariaIsolated from Sour Cherry Orchards in Michigan

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Abstract
In Michigan, Armillaria root rot severely affects Montmorency sour cherry trees growing in sandy soils. Haploid, single basidiospore cultures were established from basidiocarps of Armillaria collected from 56 sour cherry, two sweet cherry, four peach, one apple, and five oak trees. A total of 77 trees from 20 orchards and from one nonorchard site were sampled. Where basidiocarps or viable basidiospores were absent, haploid isolates were recovered from diploid isolates by inducing somatic segregation. Based on the sexual compatibility of paired isolates, three intersterile groups of Armillaria were identified among the collected isolates. These intersterility groups were compatible with North American intersterility groups I, III, and VI of Armillaria as designated by Anderson and Ullrich. From the 72 orchard trees sampled, groups I, III, and VI were collected from 58,3, and 11 trees, respectively. Group VI was also collected from five oaks at one location. North American group I, which corresponds with the taxonomic species. A. ostoyae, was widely distributed in Michigan orchards. Group VI, A. mellea sensu stricto, and group III were restricted in their distribution. All three biological species should be considered pathogens of orchard crops.

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