A project undertaken by Celeste Linde at the Australian National University, in collaboration with John Dearnaley and Stephen Neate (University of Southern Queensland), Tom May (Royal Botanic Gardens Melbourne) and Michael Weiss (University of Tubingen)
Fungi within the order Sebacinales are ubiquitous plant symbionts, having been found in 27 plant families across four continents. This project aimed to discover novel Serendipita taxa from unexplored Australian habitats and name these using morphological and molecular characterisation. Sebacinales fungi are crucial to conservation work on rare plant species where they are used to germinate seed ex situ and to assist with restoration work. It is important to rigorously characterise and formally describe novel species of Serendipita because species identification underpin practical applications and biosecurity.
S.communis micro-morphological features
S.secunda micro-morphologicalfeatures
S.warcupii micro-morphological features
Sebacinales is noted as the most diverse basidiomycete order. The Sebacinales are globally distributed and taxonomically diverse featuring: ectomycorrhizal, ericoid, endophytic, and orchid mycorrhizal species, both in autotrophs and heterotrophs. Sebacinales are taxonomically distinguished into two groups, Sebacinaceae and Serendipitaceae. Serendipitaceae, is the main focus in this study and contains only one fungal genus Serendipita, which is mainly associated with orchids, ericoid mycorrhizae and as liverwort symbionts. In Australia, Serendipita was originally isolated and identified by Warcup as Serendipita (formerly Sebacina) vermifera. Serendipita vermifera in recent years has come to be recognized as a “morphospecies” encompassing what is actually a cryptic species complex and was shown to be far more diverse than previously thought.
To discover some of the Serendipitaceae diversity in Australia, we attempted Serendipita isolation from terrestrial orchids Caladenia and Eriochilus, from epiphytic Bulbophyllum orchids including B. bracteatum, B. elisae, B. globuliforme, B. lamingtonense and B. shepherdii, as well as from liverworts. Although we were unable to isolate Serendipita from liverworts, multiple Serendipita taxa were isolated from Caladenia and Eriochilus. A phylogenetic analyses of DNA sequences using the loci ITS, nLSU and four other loci, as well as morphological characteristics, revealed at least eight novel taxa of Serendipita from Caladenia. Seven of those have been described in a manuscript which is currently in revision in Mycologia. These include S. australiana, S. communis, S. occidentalis, S. rara, S. secunda, S. talbotiii and S. warcupii. The species range from being binucleate to having up to five nuclei per cell, and all have moniliod cells.
Serendipita fungi from Eriochilus (E. cucullatus and E. dilatatus) were even more diverse than from Caladenia. In total, we isolated 28 operational taxonomic units from Eriochilus. The majority of these fungal taxa cannot be found in other orchids. Although similar levels of fungal diversity in an orchid genus can be found in Europe, it is unprecedented in Australia.By being able to associate with multiple different fungal partners, Eriochilus plants maximise their nutrition benefits, given different fungal lineages have different nutrient uptake abilities. Furthermore, having a range of fungal partners may enable the orchid hosts to to survive in multiple habitats, or even switch fungal partners under extreme environmental conditions, such as drought. One of the Serendipita taxa from E. cucullatus in Queensland have been described as S_. whamiae_ in this project.
Serendipita also associates with epiphytic orchids such as Bulphyllum. We attempted to isolate Serendipita fungi from multiple Bulbophyllum orchids including B. bracteatum, B. elisae, B. globuliforme, B. lamingtonense and B. shepherdii. We had success in isolating the target fungi from three of these orchid species. The fungus from B. bracteatum is very slow growing, has morphology typical of a Serendipita species but proved problematic to DNA sequence. The Serendipita species from Bulbophyllum globuliforme (derived from the upper canopy of a 30m hoop pine) appears to be most closely related to an isolate from Eriochilus cucullatus and two Serendipita species previously obtained from B. exiguum and B. elisae. The _Serendipita_species from B. lamingtonense is identical to a taxon that was previously obtained from B. schillerianium (this study) suggesting that this distinctive new Serendipita species is widespread in south east Queensland (ie. the collection locations were 140km apart).
We had difficulties with inducing teleomorphs from Serendipita taxa apart from S. whamiae with the soil over agar method, the buried slide method and the nutrient agar transfer method. Since the type of Serendipita was originally isolated from the fruiting bodies of a Corticium species (Oberwinkler 1956) we attempted teleomorph formation by co-culturing Serendipita with pure isolates of multiple Australian macrofungal species including Ganoderma spp., Auricularia auricula-judae, Trametes spp., Pycnoporus coccineus, and Rigidoporus vinctus. After several month in vitro growth there was no indication of teleomorph production.
An extremely large diversity of Serendipita fungi has been discovered in this project. Eight of these taxa have been described as species. However, Australia is still seemingly rich in Serendipita diversity which needs to be investigated in future studies. For example, here we investigated the Serendipita endophytes of only two Eriochilus species, yielding 28 Serendipita taxa. There are a further 17 Eriochilus species in Australia that has never been investigated for their fungal diversity. Furthermore, there is growing evidence that these serendipitas may be used in agricultural applications to enhance crop growth.
Figure 1. A leafy liverwort, Chiloscyphus semiteres
Figure 2. Bulbophyllum exiguu
Figure 3. Caladenia flava
Figure 4. Glossodia major
