New species of Tulasnella associated with Australian terrestrial orchids in the Cryptostylidinae and Drakaeinae

Analyzing the quality differences between healthy and moldy cigar tobacco leaves during the air-curing process through fungal communities and physicochemical components

Introduction

The air-curing process of cigar tobacco, as a key step in enhancing the quality of cigars, is often susceptible to contamination by mold spores, which severely constrains the quality of cigar tobacco.

Methods

This study employed high-throughput Illumina sequencing technology and a continuous flow analysis system to analyze the differences between the microbial communities and physicochemical components of moldy and healthy cigar tobacco leaves. Furthermore, correlation analysis was performed to reveal the impact of mold on the quality of cigar tobacco.

Results

The differences between the microbial flora and physicochemical compositions of moldy (MC) and healthy (HC) tobacco leaves were analyzed, revealing significant disparities between the two groups. Aspergillus spp. represented the dominant mold in MC, with nine out of twelve isolated molds showing higher quantities on MC than on HC. Mold contamination notably decreased the total nitrogen (TN), total phosphorus (TP), total alkaloids (TA), starch, protein, and flavor constituents while increasing the total fatty acid esters (TFAA), which was accompanied by a shift towards weakly acidic pH in the leaves. Fungal community analysis indicated a significant reduction in the fungal operational taxonomic unit (OUT) numbers and diversity indices in MC, contrasting with the bacterial trends. Aspergillus exhibited significantly higher relative abundance in MC, with LEfSe analysis pinpointing it as the primary driver of differentiation. Furthermore, significant negative correlations were observed between Aspergillus and TP, starch, TA, and protein, while a significant positive association was evident with TFAA. Network analysis underscored the pivotal role of Aspergillus as the species influencing disparities between HC and MC, with its abundance serving as a critical determinant during the air-curing process.

Discussion

This study elucidated substantial quality distinctions between MC and HC during air-curing, with Aspergillus emerging as the key species contributing to leaf mold.

PacBio high-throughput multi-locus sequencing reveals high genetic diversity in mushroom-forming fungi

Multi-locus sequence data are widely used in fungal systematic and taxonomic studies to delimit species and infer evolutionary relationships. We developed and assessed the efficacy of a multi-locus pooled sequencing method using PacBio long-read high-throughput sequencing. Samples included fresh and dried voucher specimens, cultures and archival DNA extracts of Agaricomycetes with an emphasis on the order Cantharellales. Of the 283 specimens sequenced, 93.6% successfully amplified at one or more loci with a mean of 3.3 loci amplified. Our method recovered multiple sequence variants representing alleles of rDNA loci and single copy protein-coding genes rpb1, rpb2 and tef1. Within-sample genetic variation differed by locus and taxonomic group, with the greatest genetic divergence observed among sequence variants of rpb2 and tef1 from corticioid Cantharellales. Our method is a cost-effective approach for generating accurate multi-locus sequence data coupled with recovery of alleles from polymorphic samples and multi-organism specimens. These results have important implications for understanding intra-individual genomic variation among genetic loci commonly used in species delimitation of fungi.

Culture age of Tulasnella affects symbiotic germination of the critically endangered Wyong sun orchid Thelymitra adorata (Orchidaceae)

Orchids (Orchidaceae) are dependent on mycorrhizal fungi for germination and to a varying extent as adult plants. We isolated fungi from wild plants of the critically endangered terrestrial orchid Thelymitra adorata and identified them using a multi-region barcoding approach as two undescribed Tulasnella species, one in each of phylogenetic group II and III (OTU1) of the Tulasnellaceae. Using symbiotic propagation methods, we investigated the role of Tulasnella identity (species and isolate) and age post isolation, on the fungus's ability and efficacy in germinating T. adorata. The group II isolate did not support germination. Seed germination experiments were conducted using either (i) three different isolates of OTU1, (ii) 4- and 12-week-old fungal cultures (post isolation) of a single isolate of OTU1, and (iii) T. subasymmetrica which is widespread and known to associate with other species of Thelymitra. Culture age and fungal species significantly (P < 0.05) affected the time to germination and percentage of seed germination, with greater and faster germination with 4-week-old cultures. Tulasnella subasymmetrica was able to germinate T. adorata to leaf stage, although at slightly lower germination percentages than OTU1. The ability of T. adorata to germinate with T. subasymmetrica may allow for translocation sites to be considered outside of its native range. Our findings on the age of Tulasnella culture affecting germination may have applications for improving the symbiotic germination success of other orchids. Furthermore, storage of Tulasnella may need to take account of the culture age post-isolation, with storage at - 80 °C as soon as possible recommended, post isolation.

Isolation of Tulasnella spp. from Cultivated Paphiopedilum Orchids and Screening of Germination-Enhancing Fungi

Ex situ conservation, an important way to increase the survival and sustainability of endangered species, is widely used in the conservation of endangered orchids. However, long-term ex situ conservation might affect the dominant group of orchid symbiotic fungi, which are crucial for orchid growth and reintroduction. This study investigated the culturable Tulasnella spp. associated with Paphiopedilum orchids after long-term greenhouse cultivation, and identified germination-enhancing isolates. A total of 44 Tulasnella isolates were obtained from the roots of 14 Paphiopedilum spp., and 29 of them were selected for phylogenetic analysis. They clustered mainly with Tulasnella deliquescens, Tulasnella calospora, Tulasnella bifrons, and Tulasnella irregularis, but included two potential new groups. Compared with published uncultured data, most of the isolates were grouped together with the reported types, and the dominant Tulasnella associated with P. armeniacum and P. micranthum could still be isolated after ten years of cultivation, most of which were the first isolation. In vitro symbiotic germination showed that certain root isolates could promote seed germination (e.g., parm152 isolated from P. armeniacum, Php12 from P. hirsutissimum, and prhi68 from P. rhizomatosum). These data indicated that the dominant Tulasnella types colonizing the roots of cultivated Paphiopedilum are stable over time, and germination-enhancing fungi colonizing the roots would benefit for seed reproduction after population reintroduction into the wild.

Strong phylogenetic congruence between Tulasnella fungi and their associated Drakaeinae orchids

The study of congruency between phylogenies of interacting species can provide a powerful approach for understanding the evolutionary history of symbiotic associations. Orchid mycorrhizal fungi can survive independently of orchids making cospeciation unlikely, leading us to predict that any congruence would arise from host-switches to closely related fungal species. The Australasian orchid subtribe Drakaeinae is an iconic group of sexually deceptive orchids that consists of approximately 66 species. In this study, we investigated the evolutionary relationships between representatives of all six Drakaeinae orchid genera (39 species) and their mycorrhizal fungi. We used an exome capture dataset to generate the first well-resolved phylogeny of the Drakaeinae genera. A total of 10 closely related Tulasnella Operational Taxonomic Units (OTUs) and previously described species were associated with the Drakaeinae orchids. Three of them were shared among orchid genera, with each genus associating with 1-6 Tulasnella lineages. Cophylogenetic analyses show Drakaeinae orchids and their Tulasnella associates exhibit significant congruence (p < 0.001) in the topology of their phylogenetic trees. An event-based method also revealed significant congruence in Drakaeinae-Tulasnella relationships, with duplications (35), losses (25), and failure to diverge (9) the most frequent events, with minimal evidence for cospeciation (1) and host-switches (2). The high number of duplications suggests that the orchids speciate independently from the fungi, and the fungal species association of the ancestral orchid species is typically maintained in the daughter species. For the Drakaeinae-Tulasnella interaction, a pattern of phylogenetic niche conservatism rather than coevolution likely explains the observed phylogenetic congruency in orchid and fungal phylogenies. Given that many orchid genera are characterized by sharing of fungal species between closely related orchid species, we predict that these findings may apply to a wide range of orchid lineages.

Isolation and identification of beneficial orchid mycorrhizal fungi in Paphiopedilum barbigerum (Orchidaceae)

Seed germination and seedling development in nearly all orchid species rely on a symbiotic relationship with mycorrhizal fungi; however, this is not the case with all mycorrhizal fungi. This study aims to provide an understanding about the important role of mycorrhiza in seed germination and growth of Paphiopedilum barbigerum. Therefore, we isolated and identified endophytic fungi from the roots of wild P. barbigerum. The beneficial mycorrhizal fungi Epulorhiza sp. FQXY019 and Tulasnella calospora FQXY017 were screened by seed symbiotic germination tests and found to promote seed germination. However, only the seeds inoculated with FQXY019 progressed from the seed germination to rooting stage. This shows that mycorrhizal fungi and P. barbigerum have a specific relation at different growth phases. In addition, we selected FQXY019 and inoculated it into MS medium, B5 medium, OMA medium, and PDA medium. The results showed that FQXY019 co-cultured on PDA significantly promoted the increase in seedling fresh weight, leaf length, and root length (p < .01). Furthermore, it significantly promoted the root number and leaf number of seedlings compared with those co-cultured on MS, B5, and OMA media and control (p < .05). Thus, this study demonstrated the promoting effect of Epulorhiza sp. FQXY019 on seed germination and seedling development, making it an alternative method for the artificial propagation of P. barbigerum.

New species of Tulasnella associated with Australian terrestrial orchids in the subtribes Megastylidinae and Thelymitrinae

Tulasnella (Tulasnellaceae) is a genus of fungus that can form mycorrhizal associations with orchids (Orchidaceae). Here we used molecular phylogenetic analyses and morphological characteristics of pure cultures across four different media to support the description of five new Tulasnella species associated with commonly occurring and endangered Australian orchids. Tulasnella nerrigaensis associates with Calochilus; T. subasymmetrica and T. kiataensis with Thelymitra; and T. korungensis and T. multinucleata with Pyrorchis and Rimacola respectively. The newly described species were primarily delimited by analyses of five loci: nuc rDNA internal transcribed spacer region ITS1-5.8S-ITS2 (ITS), C14436 (adenosine triphosphate [ATP] synthase), C4102 (glutamate synthase), C3304 (ATP helicase), and mt large subunit 16S rDNA (mtLSU). Tulasnella subasymmetrica is introduced for some isolates previously identified as T. asymmetrica, and this latter species is characterized from multilocus sequencing of a new isolate that matches ITS sequences from the ex-type culture. Morphological differences between the new species are slight. Tulasnella multinucleata has 6-12 nuclei per hyphal compartment which is the first instance of multinucleate rather than binucleate or trinucleate hyphal compartments in Tulasnella. The formal description of these species of Tulasnella will aid in future evolutionary and ecological studies of orchid-fungal interactions.

Taxonomy and phylogeny of the basidiomycetous hyphomycete genus Hormomyces

The taxonomy of the genus Hormomyces, typified by Hormomyces aurantiacus, which based on circumstantial evidence was long assumed to be the hyphomycetous asexual morph of Tremella mesenterica (Tremellales, Tremellomycetes) or occasionally Dacrymyces (Dacrymycetales, Dacrymycetes), is revised. Phylogenies based on the three nuc rDNA markers [internal transcribed spacers (ITS), 28S large ribosomal subunit nrDNA (28S) and 18S small ribosomal subunit nrDNA (18S)], based on cultures from Canada and the United States, suggest that the genus is synonymous with Tulasnella (Cantharellales, Agaricomycetes) rather than Tremella or Dacrymyces. Morphological studies of 38 fungarium specimens of Hormomyces, including the type specimens of H. callorioides, H. fragiformis, H. paridiphilus and H. peniophorae and examination of the protologues of H. abieticola, H. aurantiacus and H. pezizoideus suggest that H. callorioides and H. fragiformis are conspecific with H. aurantiacus while the remaining species are unlikely to be related to Tulasnella. The conidial chains produced by H. aurantiacus are similar to monilioid cells of asexual morphs of Tulasnella species formerly referred to the genus Epulorhiza. The new combination Tulasnella aurantiaca is proposed and the species is redescribed, illustrated and compared with similar fungi. The ecological niche of T. aurantiaca and its possible relationship to orchid root endophytes is discussed. A key to asexual genera with similar conidium ontogeny to T. aurantiaca is provided. Citation: Mack J, Assabgui RA, Seifert KA (2021). Taxonomy and phylogeny of the basidiomycetous hyphomycete genus Hormomyces. Fungal Systematics and Evolution 7: 177-196. doi: 10.3114/fuse.2021.07.09.