- Four isolates of Glomus mosseae, collected from diverse
geographic locations, were pot cultured on varied host plants or
stored in the same soil as collected. Spores of three isolates failed
to germinate on any of five agar media while the fourth germinated
well on all media. Lack of germination on agar media was not
attributable to lack of viability as spores of all four isolates germinated
when enclosed in nylon screen bags and buried in pasteurized
soil mix containing a coleus plant. Scanning electron micrographs
determined that morphological characteristics of the four isolates
differed as well.
A new endomycorrhizal species, Glomus epigaeus, produces
abundant chlamydospores in sporocarps on the soil surface. This
species has been maintained for more than 1 year in pot culture on
various hosts and produces 8-15 sporocarps monthly from each pot.
A simple technique of shaking sporocarps in water with broken glass
chips is described for the separation of spores from sporocarps.
The epigeous habit, narrow, thin-walled, inserted hyphal
attachment and bright yellow to yellow brown wall color in transmitted
light separate G. epigaeus from Glomus macrocarpus, which
is not known to fruit epigeously and has a much broader, thick-walled,
noninserted hyphal attachment and brown wall color in transmitted
The influence of physical and chemical factors on germination
of Glomus epigaeus spores was tested in nonsterile soil. Soil moisture,
temperature, and to a lesser degree, pH, appear to influence
germination, while the levels of soil fertility and spore density tested
had little or no effect. Maximum spore germination occurred in soil
at or above field capacity, between 18-25° C and between 6-8 pH.
These conditions seem closely related to the conditions optimal for
growth of many host plants, and this relationship is discussed.
Spore germination of Glomus epigaeus was completely inhibited
in forest, dune and agricultural soils which were autoclaved, and in
Chehalis silt loam which was gamma-irradiated or pasteurized as
well as autoclaved. However, 65-80% germination occurred in most
nonsterile soils, autoclaved or nonsterile kaolin and activated charcoal.
Similar levels of germination occurred on nonsterile Chehalis
silt loam containing nonmycorrhizal, ectomycorrhizal and VA
mycorrhizal seedlings, although penetration and infection was evident
only in VA mycorrhizal host seedlings.