Non-specificity of Orchid Mycorrhizal Fungi

Abstract

While isolating the mycorrhizal fungi from various species of native Wisconsin orchids, several features were noted which are at variance with the usually reported results of European investigators concerning the specificity of mycorrhizal infections. Thirty-three isolations have been made from temperate species, of which at least 16 are morphologically different. All of the strains possess typical Rhizoctonia “spore-forms” as described by Bernard for fungi from tropical and European orchids. One also has a perfect stage with basidia, but its exact taxonomic status has not yet been determined. There is an apparent correlation between ecological habitat and fungus type, rather than between orchid species and fungus, For example, Habenaria leucophaea from a tamarack-sphagnum bog was infected with a different strain of Rhizoctonia from that found in the same orchid growing in an open prairie. The two fungus strains differed markedly in spore size, growth characteristics and physiological properties. On the other hand, 4 other orchid species from the above sphagnum bog, Habenaria dilatata, H. hyperborea, H. lacera, and Pogonia ophioglossoides, were all infected with a fungus strain morphologically identical with that from the bog H. leucophaea. In another instance, 3 widely separated orchid species, Goodyera pubescens, Habenaria psycodes, and Liparis liliifolia, growing in and on the sides of a rocky pine-covered ravine, all contained the same fungus. The extent of this non-specific infection is seen in the number of distinct strains found in the same orchid species from diverse localities in Wisconsin. Thus 3 Rhizoctonia strains were isolated from Spiranthes cernua, 3 from Pogonia ophioglossoides, and 4 from Habenaria leucophaea. Perhaps the most significant finding was the growth of 2 entirely different strains of Rhizoctonia from opposite ends of the same root piece of Habenaria leucophaea on the isolation plate.