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concepts within the order Glomales (Zygomycetes) still are in their formative
stages and require input from different character sets. Morphological and
developmental characters in the genus Gigaspora were compared among
nine isolates of five species. To test plasticity of these characters, replicate
cultures of the fungi were grown on Sorghum bicolor and Asparagus
officinalis under controlled conditions. Sequences of spore wall development
were divided into three discrete stages that were identical in all Gigaspora
isolates. Neither development nor adult spore morphology of isolates
varied significantly between the two host plant species, suggesting strong
constraints on plasticity. Gross morphological characteristics of mycorrhizae
and extramatrical auxiliary cells did not differ among the various isolates.
However, spore size and color varied significantly among species, validating
current morphological species concepts within Gigaspora. Comparisons
of spore wall development in this study provide a biological rationale for
character concepts because characters now can be rooted in a process (development)
rather than from static observation. These developmental characters provide
the basis for a model of diversity in Gigaspora and its sister
genus, Scutellospora. In this monograph, the genus Gigaspora is
redescribed, along with each species. Three species are rejected as synonyms
of other species and a dichotomous key to the remaining species of Gigaspora
is presented. |
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