The influence of Streptomyces avermiti/is, 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 doublelayer WA with S. orient a/is 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. orienta/is on double-layer WA but was stimulated by S. orientalis in four-compartment petri plates when

the two organisms were in separate quadrant.s. 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.