E&E PhD Exit Seminar: Mycorrhizal potential and disease suppression of Australian orchid Serendipita species in barley

ABSTRACT

Serendipita is a genus of beneficial root-associated fungi (Basidiomycota) that promotes plant growth, enhances nutrient acquisition, and improves plant resilience to environmental stresses. Australia represents a global centre of Serendipita diversity, yet many orchid-associated species remain undescribed, and their agricultural potential is poorly understood. This study investigated the diversity, species boundaries, phylogenetic relationships, and plant growth-promoting potential of Australian orchid-associated Serendipita isolates.

An integrative species delimitation approach combining ITS phylogenetic analysis, Species Hypotheses (SHs) from the UNITE database, BLAST-derived sequences (≥ 93% similarity), and ASAP species partitioning identified five novel Serendipita species. The study highlights potential limitations of relying solely on fixed percentage sequence divergence thresholds for species delimitation in Serendipita. Similarly, assigning SH in UNITE database needs to be re-evaluated as some of the SHs may not always correspond to biologically meaningful species boundaries. Mycorrhizal potential studies showed that orchid-associated Serendipita isolates successfully colonized barley (Hordeum vulgare) roots, although colonization patterns and plant responses varied considerably among isolates, indicating substantial functional diversity within Serendipita. Some of these Serendipita isolates also changed nutrient transporter gene expression in barley in a nutrient-dependent manner, demonstrating functional interactions with a cereal host despite limited evidence of enhanced nutrient uptake. Finally, a passive nurse-plant colonization system was developed to facilitate fungal transfer between plants, demonstrating an effective approach for greenhouse inoculation or hydroponic growth systems. Although Serendipita colonization did not reduce spot blotch disease caused by Bipolaris sorokiniana, the results confirm the capacity of Australian orchid-associated isolates to establish stable associations with barley roots under diverse experimental conditions. Collectively, this research expands knowledge of Australian Serendipita diversity and provides a foundation for future studies exploring their application in sustainable agriculture.

BIOGRAPHY

Hosna Ara Chowdhury Nisha is a plant pathologist with a strong interest in plant-fungi interactions, particularly beneficial fungi. Her interest in this area began during her undergraduate studies and deepened during her Master’s in Plant Pathology, where her thesis focused on the characterization of Stemphylium vesicarium causing leaf blight of onion. She started her academic career as a Lecturer in the Department of Plant Pathology at Sher-e-Bangla Agricultural University in Bangladesh in 2014 and is currently on study leave. In 2022, she began her PhD at The Australian National University, Research School of Biology, under the supervision of Celeste Linde (ANU), John Dearnaley (UniSQ), and Peter Solomon (ANU). Her PhD research focused on the diversity and mycorrhizal potential of orchid-associated Serendipita fungi, including their ability to colonize barley roots, promote plant growth and the expression of nitrogen (N) and phosphorus (P) transporter genes, and affect plant responses to foliar pathogens. After completing her degree, she aims to continue research on beneficial plant-fungal interactions and their applications in sustainable agriculture.