Abstract
Examination of fungal specimens collected in the Atlantic rain forest ecosystems of Northeast Brazil revealed many potentially new epigeous and semihypogeous glomerocarp-producing species of the phylum Glomeromycota. Among them were two fungi that formed unorganized epigeous glomerocarps with glomoid spores of almost identical morphology. The sole structure that distinguished the two fungi was the laminate layer 2 of their three-layered spore wall, which in spores of the second fungus crushed in PVLG-based mountants contracted and, consequently, transferred into a crown-like structure. Surprisingly, phylogenetic analyses of sequences of the 18S-ITS-28S nuc rDNA and the rpb1 gene indicated that these glomerocarps represent two strongly divergent undescribed species in the family Glomeraceae. The analyses placed the first in the genus Dominikia, and the second in a sister clade to the monospecific generic clade Kamienskia with Kamienskia bistrata. The first species was described here as Dominikia glomerocarpica sp. nov. Because D. glomerocarpica is the first glomerocarp-forming species in Dominikia, the generic description of this genus was emended. The very large phylogenetic distance and the fundamental morphological differences between the second species and K. bistrata suggested us to introduce a new genus, here named as Epigeocarpum gen. nov., and name the new species Epigeocarpum crypticum sp. nov. In addition, our analyses also focused on an arbuscular mycorrhizal fungus originally described as Rhizophagus neocaledonicus, later transferred to the genus Rhizoglomus. The analyses indicated that this species does not belong to any of these two genera but represents a new clade at the rank of genus in the Glomeraceae, here described as Silvaspora gen. nov.
Highlights
In the phylum Glomeromycota, the largest group is represented by species producing glomoid spores, which arise blastically at tips of cylindrical or funnel-shaped sporogenous hyphae, as spores of Glomus macrocarpum, the type species of Glomus and the Glomeromycota (Clements and Shear, 1931; Schüßler and Walker, 2010; Oehl et al, 2011)
As we expected based on exploratory morphological and molecular phylogenetic analyses, our extended phylogenetic analyses of sequence alignments containing representatives of all genera of the Glomeraceae, using 18S-ITS-28S and rpb1 data, unambiguously and strongly confirmed our hypothesis that the two glomerocarps found in Northeast Brazil are two new species of the Glomeromycota (Figures 1–3)
The divergences of 18S-ITS-28S and rpb1 sequences between the new species, D. glomerocarpica and E. crypticum, were 18.5–19.0% and 11.0–11.8%, respectively. Another interesting finding in our analyses was that the sister species of D. glomerocarpica was D. aurea (Figures 1–3), which presents significant morphological differences
Summary
In the phylum Glomeromycota, the largest group is represented by species producing glomoid spores, which arise blastically at tips of cylindrical or funnel-shaped sporogenous hyphae, as spores of Glomus macrocarpum (see Supplementary Table 1 for species authors), the type species of Glomus and the Glomeromycota (Clements and Shear, 1931; Schüßler and Walker, 2010; Oehl et al, 2011). Of the 330 known species of the Glomeromycota, approximately 60 were originally described to form glomoid spores in epigeous or hypogeous unorganized glomerocarps, i.e., fruit bodies with randomly distributed spores inside them (Gerdemann and Trappe, 1974; Morton, 1988; Jobim et al, 2019). Of the glomerocarpic species, only seven (Diversispora epigaea, Funneliformis mosseae, Glomus arborense, G. macrocarpum, Glomus pallidum, Glomus tenerum, and Glomus warcupii) were managed to grow in culture, and only eight (D. epigaea, Diversispora sporocarpia, G. macrocarpum, Redeckera megalocarpa, Redeckera fulva, Redeckera pulvinata, Sclerocarpum amazonicum, and Sclerocystis sinuosa) were provided with molecular data (Jobim et al, 2019), which essentially makes this group of fungi ascribed to the Glomeromycota difficult to characterize and classify. Previously found from our studies in the Brazilian Northeast, there were two whose glomoid spores first seemed to be identical in morphology to each another but differed from glomoid spores of described species of the Glomeromycota.
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