Javier Palenzuela

Advances in Glomeromycota taxonomy and classification

Concomitant morphological and molecular analyses have led to major breakthroughs in the taxonomic organization of the phylum Glomeromycota. Fungi in this phylum are known to form arbuscular mycorrhiza, and so far three classes, five orders, 14 families and 29 genera have been described. Sensu lato, spore formation in 10 of the arbuscular mycorrhiza-forming genera is exclusively glomoid, one is gigasporoid, seven are scutellosporoid, four are entrophosporoid, two are acaulosporoid, and one is pacisporoid. Spore bimorphism is found in three genera, and one genus is associated with cyanobacteria. Here we present the current classification developed in several recent publications and provide a summary to facilitate the identification of taxa from genus to class level.

Otospora bareai, a new fungal species in the Glomeromycetes from a dolomitic shrub land in Sierra de Baza National Park (Granada, Spain)

A new fungal species of the Glomeromycetes was isolated from the rhizosphere of Pterocephalus spathulatus and Thymus granatensis, two rare endemic plants growing on dolomite in the Sierra de Baza (Granada, southern Spain). The fungus was propagated in pot cultures of Sorghum vulgare and Trifolium pratense for 4 y and it is described here on the basis of the spores found in nature and formed in pot cultures. Its brown spores (140–210 μm diam) form laterally on a persistent, brown stalk (=neck) of a sporiferous saccule. They have two walls without ornamentation: a brown, three- to four-layered outer wall and a hyaline two- to three-layered inner wall. The unique combination of spore formation and spore wall structure does not fit with any of the known fungal genera. Spore formation is similar to that of Acaulospora spp. and Archaeospora trappei, but Acaulospora spp. has three spore walls with a characteristic “beaded” wall, and the outer wall of Ar. trappei is simple, thin, hyaline and only bilayered. Spore wall structure of the new fungus is similar to that of Entrophospora infrequens, however this fungus forms its spores internally, inside the hyphal stalk of the sporiferous saccule. Molecular analyses of the small subunit of the ribosomal gene phylogenetically place the new fungus next to Diversispora spurca, which forms one-walled glomoid spores (i.e. terminally on hyphae). Based on these analyses we place the new fungus into a new genus in the family Diversisporaceae under the epithet Otospora bareai.

Entrophospora nevadensis, a new arbuscular mycorrhizal fungus from Sierra Nevada National Park (southeastern Spain).

A new fungal species in the arbuscular mycorrhiza-forming Glomeromycetes, Entrophospora nevadensis, was isolated from soil near the roots of several endemic and endangered plant species (e.g. Plantago nivalis and Alchemilla fontqueri) growing in Sierra Nevada National Park (Granada, Andalucía, Spain). The fungus was propagated in trap cultures on Plantago nivalis and Sorbus hybrida and in pure cultures on Trifolium pratense and Sorghum vulgare. Spores are yellow brown to brown, 90–115 μm diam and form singly in soil, in the neck of adherent sporiferous saccules that form either terminally or intercalary on mycelial hyphae. Spores have two three-layered walls and conspicuous, 6–12 μm long, spiny, thorn-like projections on the outer wall consisting of hyaline to subhyaline, evanescent tips and yellow brown to brown, persistent bases. In aging spores these projections are usually shorter (1–2.8 μm) and dome-shaped or rounded, sometimes with a central pit on top where the evanescent tip has sloughed off. Molecular analysis with partial sequences of the 18S ribosomal gene places the fungus within the Diversisporales. The new fungus was found in soil near plants with different living strategies but growing in high altitude soils with acidic pH, high soil moisture and organic carbon content, and close to streams.

Ambispora granatensis, a new arbuscular mycorrhizal fungus, associated with Asparagus officinalis in Andalucía (Spain)

A new dimorphic fungal species in the arbuscular mycorrhiza-forming Glomeromycota, Ambispora granatensis, was isolated from an agricultural site in the province of Granada (Andalucía, Spain) growing in the rhizosphere of Asparagus officinalis. It was propagated in pot cultures with Trifolium pratense and Sorghum vulgare. The fungus also colonized Ri T-DNA transformed Daucus carota roots but did not form spores in these root organ cultures. The spores of the acaulosporoid morph are 90–150 μm diam and hyaline to white to pale yellow. They have three walls and a papillae-like rough irregular surface on the outer surface of the outer wall. The irregular surface might become difficult to detect within a few hours in lactic acid-based mountings but are clearly visible in water. The structural central wall layer of the outer wall is only 0.8–1.5 μm thick. The glomoid spores are formed singly or in small, loose spore clusters of 2–10 spores. They are hyaline to pale yellow, (25)40–70 μm diam and have a bilayered spore wall without ornamentation. Nearly full length sequences of the 18S and the ITS regions of the ribosomal gene place the new fungus in a separate clade next to Ambispora fennica and Ambispora gerdemannii. The acaulosporoid spores of the new fungus can be distinguished easily from all other spores in genus Ambispora by the conspicuous thin outer wall.

Acaulospora pustulata and Acaulospora tortuosa , two new species in the Glomeromycota from Sierra Nevada National Park (southern Spain)

Two new Acaulospora species were found in two wet mountainous grassland ecosystems of Sierra Nevada National Park (Spain), living in the rhizosphere of two endangered plants, Ophioglossum vulgatum and Narcissus nevadensis, which co-occurred with other plants like Holcus lanatus, Trifolium repens, Mentha suaveolens and Carum verticillatum, in soils affected by ground water flow. The two fungi produced spores in pot cultures, using O. vulgatum, N. nevadensis, H. lanatus and T. repens as bait plants. Acaulospora pustulata has a pustulate spore ornamentation similar to that of Diversispora pustulata, while A. tortuosa has surface projections that resemble innumerous hyphae-like structures that are more rudimentary than the hyphae-like structures known for spores of Sacculospora baltica or Glomus tortuosum. Phylogenetic analyses of sequences of the ITS and partial LSU of the ribosomal genes reveal that both fungi are new species within the Acaulosporaceae. They are most closely related to A. alpina and undescribed Acaulospora species. With 45–72 μm spore size, Acaulospora pustulata is the smallest Acaulospora species known so far, while A. tortuosa has slightly larger spores (61–84(–94) μm), which is in the range known for several other Acaulospora species like A. longula, A. alpina, A. nivalis and A. sieverdingii that have either smooth or pitted spore surfaces. These two fungi might play an important role in helping their endangered hosts O. vulgatum and N. nevadensis to survive under the stressed environments of the high mountains of Sierra Nevada.

Diversispora clara (Glomeromycetes)— a new species from saline dunes in the Natural Park Cabo de Gata (Spain)

A new species of Diversispora (Glomeromycetes) was found in saline sand dunes of the Natural Park Cabo de Gata (Almeria, Andalucia, Southern Spain) in the rhizosphere of Asteriscus maritimus, a plant species especially adapted to saline environments. The new fungal species forms brilliant white spores that are 79-130 × 75-125 µm and have one wall consisting of three layers. The subtending hyphae are, as typical for many spp., thin-walled, hyaline, and cylindrical (or rarely constricted) and flexible and fragile below the septa separating the spore and hyphal contents. The septa form regularly at the spore bases or, less frequently, in subtending hyphae at short distances from the spore base. Phylogenetic analyses of the ITS and partial 28S ribosomal gene confirm that D. clara forms a monophyletic, independent clade within Diversispora .

Acaulospora viridis , a new species in the Glomeromycetes from two mountain ranges in Andalucía (Spain)

A new Acaulospora species was found in two adjacent mountains ranges in Andalucía (southern Spain), i.e. in Sierra Nevada National Park at 1270–3200 m asl around roots of Artemisia umbelliformis, Sorbus hybrida, Laserpitium longiradium among others, and in a shrubland and grassland at 1855–2028 m asl in the Sierra de Baza Natural Park. The fungus produced spores in single species cultures, using Sorghum vulgare or Trifolium pratense as bait plant. The new species was named A. viridis because of its greenish appearance under the dissecting and in the compound microscope. The spores have a smooth surface and are similar in size to several other Acaulospora species, such as A. koskei, A. laevis, A. capsicula, A. colliculosa and A. entreriana. However, the new species can easily be distinguished from all these fungi by the diagnostic staining of the middle wall in Melzer’s reagent. Phylogenetic analyses of sequences obtained from the ITS and partial LSU of the ribosomal genes confirm the new species in a clearly separate clade within the Acaulosporaceae.

Septoglomus altomontanum, a new arbuscular mycorrhizal fungus from mountainous and alpine areas in Andalucía (southern Spain).

A new arbuscular mycorrhizal (AM) fungus was found in Sierra Nevada National Park of Andalucía (Southern Spain). It forms intraradical hyphae, vesicles and arbuscles, typical characteristics of Glomeromycetes. The spores are dark reddish brown to dark reddish black, 132–205 μm diam, and are formed on pigmented subtending hyphae whose pores are regularly closed by a thick septum at the spore base but without support of introverted wall thickening. Phylogenetic analyses on concatenate sequences of the partial SSU, ITS region and the partial LSU of the rDNA confirm the new species, described here as Septoglomus altomontanum, in a monophyletic clade next to S. africanum. An identification key to all Septoglomus species described is given. The new fungus can unequivocally be distinguished from all other Septoglomus species by the combination of spore size, colour and spore wall structure, and especially by the shape and colour of the subtending hyphae. Septoglomus altomontanum has so far been found only in soils with pH 5.9–6.7, located in mountainous and alpine altitudes (1800–3100 m asl) of Sierra Nevada which is well known for a high degree of plant endemism. While it is a frequent fungus in this area, it has so far not been found in lower altitudes in Andalucía.