Full paperGrosmannia tibetensis, a new ophiostomatoid fungus associated with Orthotomicus sp. (Coleoptera) in Tibetan subalpine forests
Introduction
Ophiostomatoid fungi have symbiotic relationships with bark beetles. The fungi provide a direct benefit to their beetle partners through producing bark beetle aggregation pheromones and semiochemicals (Zhao et al., 2019a). In many cases, the fungi are virulent to host plants (Brasier, 1979; Harrington, Fraedrich, & Aghayeva, 2008; Wingfield, Seifert, & Webber, 1993), and this may indirectly help the beetles overcome the defensive system of their host plants (Zhao et al., 2019b). This fungal group is polyphyletic and includes numerous genera in two orders, Ophiostomatales (Sordariomycetidae) and Microascales (Hypocreomycetidae) (de Beer & Wingfield, 2013). Ophiostoma and Leptographium sensu lato are the two genera with the greatest species diversity.
Many species of Leptographium s. l. were previously classified in different genera such as Ceratocystis, Grosmannia, or Ophiostoma. Phylogenetic analysis has been based on DNA sequence data such as the nuclear ribosomal large subunit region (LSU), internal transcribed spacer regions 1 and 2 of the nuclear ribosomal DNA operon, including the 5.8S region (ITS), the beta-tubulin gene region (BT), and the transcription elongation factor-1α gene region (EF). These analyses can reveal the relationships and provide accurate classification of the fungi. However, since a single name is now used for the fungi in this group, two generic names, including the older and broader name Leptographium and a teleomorphic name, Grosmannia, are used by taxonomists and require reevaluation (de Beer & Wingfield, 2013; Jacobs & Wingfield, 2013).
In mainland China, the taxonomy of Leptographium is now reasonably well known. Numerous studies using both morphological and DNA-based phylogenetic approaches have identified at least 37 Leptographium species, of which 23 were new (Zhou et al., 2000; Lu, Decock, Zhang, & Maraite, 2008; Lu, Decock, et al., 2009; Lu, Zhou, et al., 2009; Paciura et al., 2010; Yin, Duong, Wingfield, Zhou, & de Beer, 2014; Chang et al., 2019, 2017; Liu et al., 2017; Wang et al., 2019; Wang et al., 2020; Yin, Wingfield, Zhou, & de Beer, 2020). However, only 8 of the 34 Chinese provinces have been surveyed and large areas harboring diverse forest ecosystems remain unexplored. Thus, there is great potential for discovering new species in China. The Tibetan Plateau is an area that is unexplored for ophiostomatoid fungi.
The Tibetan Plateau is the highest and largest plateau in the world. The unique geographical conditions there have produced diverse ecosystems and created favorable environments for species maintenance and formation of new species (Gansser, 1964). As such, the Tibetan Plateau has rich biological diversity (Liu, Wang, Wang, Hideaki, & Abbott, 2006). Many native coniferous trees occur on the Tibetan Plateau (China flora editorial committee of Chinese academy of sciences, 1978). Spruces (Picea spp.) are the dominant trees in the forests. More than half of the 34 world species of Picea occur on the plateau and adjacent regions (Sun et al., 2014). Tibetan spruce forests are often infested by bark beetles (Yin, Huang, & Li, 1984). Nine ophiostomatoid fungus species have been reported in association with four bark beetle species that infest spruces on the plateau margin in Qinghai province (Yin, Wingfield, Zhou, & de Beer, 2016, 2020).
In a survey of the ophiostomatoid fungi on bark beetles infesting Picea likiangensis var. balfouriana (Rehder & E.H. Wilson) Hillier. in forests of the Tibetan Plateau, an undescribed species of Leptographium s. l., was isolated from Orthotomicus sp. adults. Their galleries were characterized by morphological observations and multilocus DNA sequence data. This species is described as Grosmannia tibetensis sp. nov. This is the first report of the presence of tubulin paralogue genes in ophiostomatoid fungi.
Section snippets
Collection of samples and fungus isolations
Fungi were isolated from adults and breeding galleries of Orthotomicus sp., infesting the bark of P. likiangensis var. balfouriana in Zuogong county (29°14′2″N; 98°2′52″E, altitude 3780 m), Tibet autonomous region. Adult beetles and their galleries were individually placed in sterile Eppendorf tubes and envelope bags, respectively. They were stored at 4 °C until fungal isolations were made. Each adult beetle was dismembered into about 15 pieces on the surface of 2% water agar without previous
Collection of samples, isolation of fungi, and sequence comparisons
Twenty adults and 50 breeding galleries of Orthotomicus sp. were collected from P. likiangensis var. balfouriana in Zuogong county, Tibet autonomous region. A total of 225 strains were obtained, of which 52 were identified as ophiostomatoid fungi based on morphological characteristics. Among them, 29 strains were derived from the adult beetles and 23 strains were derived from the galleries. The 52 strains were characterized by olivaceous colored colonies, typical Leptographium and Pesotum
Discussion
Fifty-two strains of ophiostomatoid fungi were isolated from adults and galleries of Orthotomicus sp. infesting P. likiangensis var. balfouriana in forest of the Tibetan Plateau. Using a combination of morphology and phylogeny, G. tibetensis sp. nov. was described and illustrated based on these strains. The species belongs to the “G. penicillata complex” and is the first record of ophiostomatoid fungi from Tibet.
Grosmannia penicillata is the type species of the genus. It forms a well-supported
Declaration of competing interest
The authors declare no conflicts of interest. All the experiments undertaken in this study comply with the current laws of the country where they were performed.
Acknowledgments
This work was supported by the National Natural Science Foundation of China (Project No.: 31770682, 31070571). Dr. Cony Decock gratefully acknowledges the financial support received from the Belgian State (Belgian Federal Science Policy through the BCCM™ research program). We thank LetPub (www.letpub.com) for its linguistic assistance during the preparation of this manuscript.
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These authors contributed equally.