Fungal communities associated with myrtle rust infection and their potential as biocontrol agents against the disease

Abstract

Myrtle rust, caused by Austropuccinia psidii, has spread widely across New Zealand, threatening over 19 native and 17 exotic myrtaceous species. This research aims to investigate fungal communities associated with myrtle rust infection and identify mycoparasite(s) for potential use as biocontrol agents against this pathogen. Symptomatic and asymptomatic leaf samples were collected from ramarama (Lophomyrtus bullata) and pōhutukawa (Metrosideros excelsa) across four sites (Taranaki, Rotorua, Auckland, and Christchurch) for the isolation and identification of the fungal microbiome using metabarcoding. Initial results of the fungal microbiome from plants in Taranaki showed the highest relative abundance of Colletotrichum (28.90%), Simplicillium (25.39%), and Neopestalotiopsis (4.41%) in asymptomatic leaves, while the most common genera in symptomatic leaf samples were Lophiotrema (43.63%), Septobasidium (4.43%), and Conoideocrella (3.1%). Differences in fungal communities between locations and their association with rust infection will be presented. The 201 fungal isolates recovered (148 epiphytes and 53 endophytes) were identified as belonging to 61 fungal genera. Putative mycoparasites from eleven genera (Alternaria, Aureobasidium, Cladosporium, Clonostachys, Colletotrichum, Epicoccum, Myrothecium, Paraconiothyrium, Phlebiopsis, Trichoderma and Sclerostagonospora) were selected for screening for antagonistic activity against A. psidii. Three different in vitro bioassays, including a spore germination test, culture filtrate assay and detached branchlet assay were used to assess each isolate's ability to control myrtle rust. Several isolates capable of inhibiting the germination of A. psidii spores and/or colonizing the pustules have been identified. These isolates are now undergoing further testing for biological control activity against myrtle rust in glasshouse conditions.