Diversity of Serendipitaceae Mycorrhizal Associations of Australian Terrestrial Orchids
Creators: name: Oktalira, Fitria
Publisher: name: The Australian National University
Year: 2021

description: Mycorrhizal fungi play an essential role in the orchid establishment. This study will focus on four Australian orchid genera which form orchid mycorrhizal associations with the fungus Serendipita. The expected outcome of this thesis is to construct a continent-wide phylogeny and establish a biogeographical pattern of distribution for Serendipita in Australia. In chapter one (published in Fungal Ecology), I focused on fungal symbionts in two Caladenia species-pair contrasts, each pairing one widely distributed species with a closely-related species of narrow distribution. Across four orchid species, we identified 70 fungal isolates and 121 clone sequences of the fungal genus Serendipita. The widespread C. pectinata and narrowly distributed C. procera both associate with two operational taxonomic units (OTUs). Four OTUs were identified in widespread C. tentaculata compared to one OTU in the narrow endemic C. atrovespa. Germination trials showed seeds from all orchids are compatible with more OTUs than were observed in adult plants, suggesting lower specificity during germination. Fungi germinating narrowly distributed orchids are themselves widespread and are therefore unlikely to limit orchid distribution. In chapter two, I investigated the ability of 33 isolates of nine Serendipita OTUs to utilize a range of carbon, nitrogen and phosphorus sources. This study was undertaken because I observed a wide variation in the ability of Serendipita in germinating orchid seeds, both within or/and between fungal operational taxonomic units (OTUs). This lead to the question of whether OMF lineages might also vary in metabolic traits that interact with plant nutrition. Significant variation in nutrient utilisation among and within OTUs were observed, suggesting fungal individuals have adapted to specific environments. In general, Serendipita isolates from common orchids were not significantly better at utilising nutrients than those from rare orchids. In chapter three, I investigated whether Serendipita fungi in Australia are broadly distributed and shared between south-western and south-eastern Australia, and whether regions with lower soil fertility (south-western Australia) also show a higher Serendipita diversity. Fungal distribution patterns have consequences for future conservation studies. Fungal symbiont diversity of species-pair comparisons of four orchid genera (Eriochillus, Glossodia Elythranthera, Caladenia), one species of each genus occurring in either south-western or south-eastern Australia, were investigated. At least 35 OTUs of Serendipita were identified with ITS sequencing from the eight orchid species pairs. Serendipita diversity (number of OTUs) does not differ between geographic regions. Depending on the tribe of orchids studied, some tribes were highly specialised in their fungal associations, while Eriochilidinae is a true generalist associating with 30 OTUs. In total, 14 out of the 35 OTUs were found on both sides of the continent, suggesting they have wide distribution patterns. In the last chapter, seven new Serendipita species associated with Australian orchid genera were described based on a species delimitation analysis using a multilocus DNA sequence (three mtDNA and four nuclear loci) molecular phylogenetic analysis. To aid in the description of these species, various cultural and morphological characteristics were examined. These species were identified with up to 4.31 % sequence divergence within taxa and a minimum of 3.04 % among taxa divergence. This is adding to the limited number of formally described Serendipita species globally. Given that Serendipita is commonly found in Australia associating with several orchid genera, it is likely an even larger diversity of Serendipita will be discovered in Australia in future studies.