The ectomycorrhizal morphotype Pinirhiza sclerotia is formed by Acephala macrosclerotiorum sp. nov., a close relative of Phialocephala fortinii

Abstract

Relatively few ectomycorrhizal fungal species are known to form sclerotia. Usually, sclerotia are initiated at the extraradical mycelium. In this study, we present anatomical and ultrastructural evidence for the formation of sclerotia directly in the hyphal mantle of the mycorrhizal morphotype Pinirhiza sclerotia. A dark-pigmented fungal strain was isolated from Pinirhiza sclerotia and identified by molecular tools as Acephala macrosclerotiorum sp. nov., a close relative of Phialocephala fortinii s.l. As dark septate fungi are known to be mostly endophytic, resyntheses with Pinus sylvestris and A. macrosclerotiorum as well as Populus tremula x Populus tremuloides and A. macrosclerotiorum or P. fortinii s.l. were performed under axenic conditions. No mycorrhizas were found when hybrid aspen was inoculated with A. macrosclerotiorum or P. fortinii. However, A. macrosclerotiorum formed true ectomycorrhizas in vitro with P. sylvestris. Anatomical and ultrastructural features of this ectomycorrhiza are presented. The natural and synthesized ectomycorrhizal morphotypes were identical and characterized by a thin hyphal mantle that bore sclerotia in a later ontogenetic stage. The Hartig net was well-developed and grew up to the endodermis. To our knowledge, this is the first evidence at the anatomical and ultrastructural level that a close relative of P. fortinii s.l. forms true ectomycorrhizas with a coniferous host.

Root-Associated Ectomycorrhizal Fungi Shared by Various Boreal Forest Seedlings Naturally Regenerating after a Fire in Interior Alaska and Correlation of Different Fungi with Host Growth Responses

“…Two small ribotypes contained members of the genus Phialocephala, known to contain dark septate endophytes (24,50). A Phialocephala-related fungus was found to form ectomycorrhizas on pine (but not aspen [34]). Dark septate endophytes which enhance plant growth have been observed (1,53), but there are also reports of negative and neutral effects (24).…”

Sexual and asexual states of some endophyticPhialocephalaspecies ofPicea

“…(Grünig and Sieber 2005). Acephala currently comprises two species and the generic name has been applied informally to a phylogenetically diverse range of sterile strains apparently congeneric with Phialocephala (Grünig et al 2009, Münzenberger et al 2009). The current taxonomic concept of Phialocephala is therefore polyphyletic but with most sequenced species within a lineage encompassing the VibrisseaLoramyces-Mollisia clades sensu Wang et al (2006a, b) and Grünig et al (2009).…”

Chlorovibrissea korfii sp. nov. from northern hemisphere and Vibrissea flavovirens new to China

“…1, MPBP/NJBP = 99%/99%). Acephala was thought to be congeneric with Phialocephala by some authors, and differentiated only by the lack of observed sporulation in culture (Grünig et al 2009;Münzenberger et al 2009;Tanney et al 2016). Phialocephala species are commonly isolated as dark-septate endophytes from coniferous tree roots or from decomposing wood (Menkis et al 2004), and attributed to Vibrisseaceae mainly based on sequence data (Wang et al 2006;Kirk et al 2008).…”

“…Acephala was erected for the non-sporulating species of Phialocephala that contain a small group of dark septate root endophytes (Grünig and Sieber 2005;Grünig et al 2008;Grünig et al 2009;Münzenberger et al 2009;Wang et al 2009;Day et al 2012). About 80 species are currently accepted in the family, among which two species are in Acephala, six in Chlorovibrissea, one in Leucovibrissea, 33 in Phialocephala, and 36 in Vibrissea (Grünig et al 2008;Kirk et al 2008;Grünig et al 2009;Münzenberger et al 2009;Wang et al 2009;Day et al 2012;Johnston et al 2014;Sandoval-Leiva et al 2014;Index Fungorum 2017). The previous phylogenetic studies on the vibrisseaceous fungi showed that Chlorovibrissea and Vibrissea are not closely related, and the family was presumably polyphyletic (Wang et al 2006;Sandoval-Leiva et al 2014).…”