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Axenic Germination of Vesicular-Arbuscular Mycorrhizal Fungi: Effects of Selected Streptomyces Species. G. L. Tylka, Former graduate research assistant, Department of Plant Pathology, University of Georgia, Athens, 30602, Present address: Department of Plant Pathology, Iowa State University, Ames, 50011; R. S. Hussey, and R. W. Roncadori. Professors, Department of Plant Pathology, University of Georgia, Athens, 30602. Phytopathology 81:754-759. Accepted for publication 25 February 1991. Copyright 1991 The American Phytopathological Society. DOI: 10.1094/Phyto-81-754.

The influence of Streptomyces avermitilis, S. griseus, and S. orientalis on germination of surface-disinfested Gigaspora margarita, Glomus mosseae, and Scutellispora heterogama spores on 1.5% Noble water agar (WA) was studied. G. margarita and G. mosseae germination was stimulated by S. orientalis. Spores germinated more frequently on double-layer WA with S. orientalis microcolonies suspended in the bottom layer than on WA. Experiments conducted with four-compartment petri plates indicated that stimulation was due to one or more volatile compounds. Germination of G. mosseae spores was also stimulated by S. avermitilis and S. griseus on double-layer WA but was generally poor on WA not containing Streptomyces microcolonies. G. mosseae spore germination on WA was not influenced by pH. S. heterogama spore germination was suppressed by S. avermitilis and S. orientalis on double-layer WA but was stimulated by S. orientalis in four-compartment petri plates when the two organisms were in separate quadrants. Generally, germination of S. heterogama spores was inversely related to WA pH. All three Streptomyces spp. increased pH of WA overlayers by two pH units after 9 days at 25 C.

Additional keywords: soil microorganisms.