Rhizoglomus venetianum, a new arbuscular mycorrhizal fungal species from a heavy metal-contaminated site, downtown Venice in Italy

Abstract

Rhizoglomus venetianum, a new arbuscular mycorrhizal fungal species, has been isolated and propagated from a heavy metal contaminated site in Sacca San Biagio island, downtown Venice, Italy. Interestingly, under the high levels of heavy metals occurring in the site, the new fungus was able to grow only intraradically. In greenhouse trap and single species cultures under low heavy metal levels, the fungus produced innumerous spores, clusters and sporocarps extraradically, which were formed terminally on subtending hyphae either singly, in small spore clusters, or, preferably, in loose to compact non-organized sporocarps up to 2,500 × 2,000 × 2,000 µm. Spores are golden-yellow to bright yellow brown, globose to subglobose to rarely oblong, 75-145 × 72-140 µm in diameter and have four spore wall layers. Morphologically, the new fungus is similar to R. intraradices, and phylogenetically it forms a monophyletic clade next to R. irregulare, which generally forms irregular spores and lacks, like R. intraradices, the flexible innermost wall layer beneath the structural/persistent third wall layer. A key for the species identification is presented comprising all 18 Rhizoglomus species, so far described or newly combined.

New sporocarpic taxa in the phylum Glomeromycota: Sclerocarpum amazonicum gen. et sp. nov. in the family Glomeraceae (Glomerales) and Diversispora sporocarpia sp. nov. in the Diversisporaceae (Diversisporales)

“…Of the nearly 300 species of the phylum Glomeromycota C. Walker & A. Schüßler (Schüßler et al 2001;Tedersoo et al 2018;Turrini et al 2018) comprising arbuscular mycorrhizal fungi (AMF), only 57 were originally described to form spores at the tip of sporogenous hyphae in epigeous or hypogeous sporocarps, i.e., fruit bodies, with or without a peridium and with a gleba. The peridium is a network of hyphae that partially or completely covers the gleba, which is composed of spores embedded in interwoven hyphae (Gerdemann and Trappe 1974;Morton 1988).…”

New Glomeromycotan Taxa, Dominikia glomerocarpica sp. nov. and Epigeocarpum crypticum gen. nov. et sp. nov. From Brazil, and Silvaspora gen. nov. From New Caledonia

“…The sister species to the Rhizoglomus clade was a member of the genus Sclerocystis, S. sinuosa (Crossay et al, 2018). Molecular phylogenetic analyses performed by Turrini et al (2018) confirmed the basal position and strong genetic divergence of R. neocaledonicum in the Rhizoglomus clade. However, they did not include S. sinuosa in their analyses.…”

“…Recently, a new AMF, namely, Rhizophagus neocaledonicus, was described, which in the field lived in symbiosis with metallophytes in ultramafic soil in New Caledonia (Crossay et al, 2018). It was soon reassigned to the genus Rhizoglomus, as Rhizoglomus neocaledonicum (Turrini et al, 2018), because the generic name Rhizophagus should not be assigned to any species in the Glomeromycota (Sieverding et al, 2014). The assignment of this species into the genus Rhizoglomus (treated as Rhizophagus) was made based on a maximum likelihood phylogenetic analysis of 18S-ITS-28S sequences, even though the Rhizoglomus clade with the basally positioned R. neocaledonicum obtained only 49% bootstrap support.…”

Anchoring the species Rhizophagus intraradices (formerly Glomus intraradices)

“…2008 ) , R. custos ( Cano et al . 2009 ) R. prolifer ( Declerk et al 2000 ) , R. venetianum ( Turrini et al 2018 ), R. aggregatum and R. intraradices ( Schenck & Smith 1982 )) and it is very difficult or impossible to distinguish them from spores collected from field soils. Difficulties in interpreting type species, their descriptions and the possibility of cryptic speciation in the genus Rhizophagus present serious problems for interpreting and assigning species names with confidence.…”