Sporocarpic species of arbuscular mycorrhizal fungi ( Glomeromycota ) , with a new report from Brazil

(Sporocarpic species of arbuscular mycorrhizal fungi (Glomeromycota), with a new report from Brazil). The arbuscular mycorrhizal fungi (AMF) are widely distributed in terrestrial ecossystems; however the sporocarpic species are less documented on AMF surveys. Five of these species were found in natural areas of Atlantic Forest and in agricultural ecosystems of Northeast Brazil: Glomus glomerulatum, G. sinuosum, G. coremioides, G. fuegianum and G. taiwanensis, with the last one being registered for the first time in Brazilian soils.


Introduction
Many arbuscular mycorrhizal fungi (AMF), mostly sporocarpic species, are not well known regarding their distribution.Among the AMF species, the former sporocarpic genus Sclerocystis was poorly documented in tropical countries such as Brazil.Almeida & Schenck (1990) transfered most of the Sclerocystis species to the genus Glomus, maintaining only S. coremioides.Wu (1993) did not agree with this proposal, while Redecker et al. (2000) based on molecular studies, indicated that S. coremioides belongs to a clade that contains Glomus species.Today, among the sporocarpic species of AMF, only two belong to the genus Acaulospora, all others are included in Glomus.
The term sporocarp is used for the arrangement of spores in Acrasiomycota, Myxomycota and Endogonales (Kirk et al. 2001).The AMF, initially included among the Endogonales, were transferred to Glomerales (Morton & Benny 1990) but actually constitute a phylum: Glomeromycota (Schubler et al. 2001).The term sporocarp for this group of organisms is complex, since that similar structures are refered as "cluster" of spores for some authors, while others mention such structures as "sporocarp".However, as considered by Schenck & Pérez (1990), sporocarp is a structure with spores borne closely together that may be surrounded by peridial hypha.The species earlier included in Sclerocystis have a complex arrangement of their sporocarpic structure, while other Glomus species have a less complex arrangement of spores.Species such as Glomus glomerulatum Sieverding whose spores have two subtending hypha, present a more complex hyphal arrangement, while others such as Glomus fasciculatum (Thaxter) Gerd.& Trappe emend.Walker & Koske have only one subtending hypha per spore and a less complex structure.However, other species (G.aggregatum (Schenck & Smith) emend.Koske) show characters that are intermediate, between those of G. glomerulatum and G. fasciculatum, with spores presenting one or two subtending hypha in the same sporocarp.Thus, the term sporocarp used for the AMF include species with spores in clusters and species with more complex structures such as those found in G. coremioides, G. sinuosum and G taiwanensis.This work describes sporocarpic species of AMF registered in some Brazilian soils.

Results
Five species of Glomus are described, with references to the geographical distribution in Brazil.Sieverding, 1987 (Mycotaxon 29:74).
Sporocarps subglobose to irregular.Spores globose (50-70 µm) to subglobose, all of them with 2-3 subtending hypha.Wall in a group with two layers, the first laminated, from gold yellow to dark brown and the second membranous, thin (<1.0 µm) and hyaline.Subtending hypha delicate and interwoven inside the sporocarp.Septum viewed only in one of the hypha, in spores presenting large thickness of the wall next to the point of insertion of the subtending hypha, as referred in the original description.
Sporocarps of G. glomerulatum are similar to those of G. fasciculatum, G. aggregatum and G. microaggregatum Koske, Gemma & Olexia; however in G. glomerulatum all spores present 2-3 subtending hyphae, while in the other species the spores have only one subtending hypha.The spores of G. glomerulatum that we observed possessed an external wall, as described by Sieverding (1987).
Sporocarps globose, without peridium, dark brown at the stereomicroscope and red brown at the light microscope.Presence of debris attached to the sporocarp.Spores clavate to cylindrical (84 µm long, 16.8 µm wide at the base and 18.8 µm wide at the apex), brown to slightly red, with the apex darker.Wall in a group, with the external layer thin, hyaline, evanescent and the inner layer laminated, brown.Wall thinner at the base of the spore (3.7 µm) and wider at the apex (20 µm).Spores formed in a radial distribution.Only one subtending hypha per spore.Central plexus approximately 100 µm diam.Sporophores observed in different developmental stages.
This species is similar to G. clavisporum (Trappe) Almeida & Schenck in arrangement of the spores inside the sporocarp, in form, as well as in colour.However, G. clavisporum presents two spore types: one longer and other wider, with two well defined layers of the same thickness, while G. taiwanensis have only one spore type and also presents an evanescent, hyaline layer, easily detached from the laminated wall layer (Wu 1993).
Glomus fuegianum has clusters that are much more compact than in G. australe (Berkeley) Berch.Besides, the spores of G. fuegianum "tend to be elongated, their shape resulting from multual packing in the tight clusters", as mentioned by Berch & Fortin (1983), while those of G. australe are globose.This is the first report, in Brasil, of G. fuegianum; sporocarps of this species were observed and described in Poland (Blaszkowski et al. 1998  Sporocarp globose to subglobose with peridium brown to dark brown (446×330 µm).Subtending hypha with thick wall, interwoven in a sinuose way.Central plexus around 112 µm diam.Spores elongated (94 µm long), with thin wall (2-3 µm), light brown.Septum easily observed between the spore and its subtending hypha.A hyphal stalk originating the sporocarp, as refered by Wu (1993) was not observed.
At the stereomicroscope G. sinuosum is similar to G. coremioides but differs in the thickness of the peridium as well as in the hyphal arrangement.
At the stereomicroscope, sporocarps of G. coremioides are similar to those of G. sinuosum; however differ in thickness and in the hyphal arrangement of the peridium.In G. coremioides the peridium is thick without a sinuose hyphal structure and the sporocarp is hemispheric, while that of G. sinuosum is globose to subglobose.