Terminology
The morphological description of AMF species is based on the analysis of characteristics of asexual spores, including size, color, presence of ornamentation, mode of spore formation, and on the analysis of their subcellular structures.
The contents of the pages below include information on how AMF spores are formed (sporogenesis) as well as the different terminologies proposed by Walker (1983), Morton et al. (1995) and Sieverding & Oehl (2006), used to describe the different differentiated phenotypic structures differentiated by AMF spores.
Mode of spore formation
The mode of spore formation mode (sporogenesis) refers to the pattern that the spores are formed at the beginning of their ontogeny from the fertile hypha. Although several modes of spore formation are reported in the literature for AMF, four main modes are recognized herein: glomoid, acaulosporoid, gigasporoid, and ambisporoid.
GLOMOID: Glomoid spores are formed blastically at the end of a single subtending hypha. This mode of spore formation is the most common within the Glomeromycota and shared by species in all Orders. Taylor et al. (2013) recorded glomoid spores formed in vitro by a species of Acaulospora.
Genera with glomoid mode of spore formation: Glomus, Epigeocarpus, Sclerocarpum, Funneliformis, Rhizophagus, Sclerocystis, Septoglomus, Kamienskia, Dominikia, Oehlia, Halonatospora (Family Glomeraceae), Claroideoglomus (Family Claroideoglomeraceae), Redeckera, Diversispora, Corymbiglomus, Desertispora (Family Diversisporaceae), Paraglomus, Innospora (Family Paraglomeraceae), Pervetustus (Family Pervetustaceae), Pacispora (Family Pacisporaceae), Ambispora (morfotype glomoid), and Acaulospora (considering results of Taylor et al. 2013).
ACAULOSPOROID: the acaulosporoid mode of spore formation is characterized by the formation of a sporiferous saccule prior to spore formation. The sporiferous saccule is an ephemeral structure, formed blastically at the tip of a hypha with very condensed content when young. Afterwards, the spores are differentiated laterally or inside the neck of the sporiferous saccule. Acaulosporoid spores are found in two Orders (Diversisporales and Archaeosporales) and three families (Acaulosporaceae, Archaeosporaceae, and Diversisporaceae).
Genera with acaulosporoid mode of spore formation: Acaulospora (Family Acaulosporaceae), Archaeospora, Palaeospora (Family Archaeosporaceae), Otospora, Tricispora (Family Diversisporaceae), Sacculospora (Family Sacculosporaceae), and Entrophospora (genus incertae saedis).
Obs.: species forming spores inside the neck of the sporiferous saccule were included in the genus Entrophospora. Species in this genus have been transferred to other genera based on molecular characters.
GIGASPOROID: the gigasporoid mode of spore formation is characterized by spores formed terminally in a subtending hypha with a bulbous sporogenous cell. Organisms forming gigasporoid spores are restricted to the family Gigasporaceae (order Diversisporales).
Genera with gigasporoid mode of spore formation: Gigaspora, Racocetra, Cetraspora, Scutellospora, Dentiscutata, Bulbospora, Intraornatospora, Paradentiscutata.
AMBISPOROID: this mode of spore formation can be considered a variant of the acaulosporoid mode as a sporiferous saccule is differentiated previously to the spore formation. However, in the ambisporoid mode of formation, the spores are formed at the tip of a subtending hypha (pedicel) that branches from the neck of a sporiferous saccule. This mode of spore formation is restricted to the family Ambisporaceae (order Archaeosporales). A diferença é que neste modo de formação, os esporos são formados na extremidade de uma ramificação (pedicelo) que se forma lateralmente ao sáculo esporífero. Este modo de formação é restrito a família Ambisporaceae na Ordem Archaeosporales.
Genus with ambisporoid mode of spore formation: Ambispora
Reference:
Taylor, A., Walker, C. & Bending, G.D. 2013. Dimorphic spore production in the genus Acaulospora. Mycoscience. http://dx.doi.org/10.1016/j.myc.2013.03.001
TERMINOLOGY OF:
- Morton, Bentivenga and Bever (1995)