Variation in Mycorrhizal and Spore Morphology of Glomus occultum and Glomus diaphanum as Influenced by Plant Host and Soil Environment

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Abstract
Spore and mycorrhizal morphology were examined among isolates of G. occultum and G. diaphanum collected from soils with dissimilar physical and chemical properties, and they were maintained in pot culture on 5 plant species. Spore size, color, and structure were not influenced significantly by host or soil environmental interactions. Spore wall structure consistently separated G. occultum and G. diaphanum. Intraspecific variation in overlapping taxonomic characteristics, such as spore size, did not obscure significant differences between species. These results provide further evidence that spore morphological characteristics are valid criteria for identifying and classifying VA [vesicular-arbuscular] mycorrhizal fungi. However, mycorrhizal morphology also differentiated the 2 endophyte species. Intraradical structures formed by G. occultum stained weakly within 2 wk after initial penetration of roots, and disappeared thereafter. G. diaphanum produced arbuscules, vesicles and spores in stained roots. Mycorrhizal morphology and ontogeny of each endophyte were similar in all hosts. Significant variation was expressed in the rate and degree of mycorrhizal development. Disparate, yet consistent, mycorrhizal formed by G. occultum and G. diaphanum indicate that mycorrhizal anatomy also may be important in the classification of VA mycorrhizal fungi.