Dichotomous keys for morphological identification of spores produced by arbuscular mycorrhizal fungi (phylum Glomeromycota) integrating the mode of spore formation and a spore developmental model.

Taxonomy of arbuscular mycorrhizal fungi (AMF) fungi (Glomeromycota) has long relied on spore morphological characteristics, which are distinguishable and evolutionarily stable structures in these fungi. Mode of spore formation and germination properties in AMF identify higher order taxa. Species level traits include external and internal spore morphology (e.g. size, color, spore wall structure, surface ornamentation) and some characteristics at the region of hyphal attachment. Comparative studies of AMF spore ontogeny led to a developmental model where characters were defined by their origin, position in ontogeny, and constraints on variation. The goals of this work are (i) to revisit the spore developmental model, the model's premises and interpretations for morphological taxonomy of AMF, (ii) to describe and compare the main modes of spore formation as the first step to define taxa, and (iii) to organize these data into dichotomous keys as a tool for AMF species identification. Such an aid will facilitate a more accurate identification of fungal specimens collected and investigated in field-based and ecological studies, in organization and maintenance of germplasm deposited in culture collections, and in production and utilization of commercial inoculants.