School of Applied Sciences, RMIT University (Australia) and Lund University (Sweden)
Advisors: Prof Ann Lawrie, Dr David McLaren and Dr Robin Adair
Tutsan (Hypericum androsaemum) is a noxious weed in south-eastern Australia and New Zealand. It is shade tolerant and competitive, establishing quickly in disturbed areas and growing on south-facing slopes and cliffs in forests and pastures. A rust fungus (Melampsora hypericorum) has shown to be highly specific to tutsan and caused 99% eradication of the weed in Apollo Bay in the 1990s. Currently, herbicides are the primary method used to control tutsan; but biological control using artificial inoculation with tutsan rust may be more cost-effective and self-sustaining.
Recent observations found that virulence of tutsan rust infection differs across populations, so a fundamental of plant pathology – the disease triangle – was used to investigate the cause of this by researching the host, pathogen and environment in turn. Genetic and phylogenetic analysis of tutsan and tutsan rust showed variation in the populations of both host and pathogen. A potential relationship between host and pathogen ITS-sequence phylogenies was found. Species-specific primers were designed to isolate regions of M. hypericorum DNA for further phylogenetic analysis.
A cross-inoculation trial was conducted and the results were investigated using Scanning Electron Microscopy (SEM), however there was no sign of tutsan rust infection. Field observations showed that tutsan rust prefers a wetter climate than the range tolerated by tutsan, and environmental similarities between rust infected tutsan populations were correlated with phylogenetic grouping of tutsan rust ITS sequences. Changes to the inoculation program currently used by the DPI to inoculate tutsan populations with tutsan rust, are recommended to reflect this.
Top left: Map of Victoria and New South Wales collection and observation sites
Top right: ITS phylogeny of six Hypericorum androsaemum populations collected from Apollo Bay, Black Spur, Ned’s Gully, Falls Rd and Harrietville in Victoria, and Jenolan in New South Wales. Bootstrap support values indicated at the nodes. Chrysochlamys glauca is used as the outgroup (bold). Populations infected with Melampsora hypericorum are indicated in red. Derived clades are grouped as shown in blue.
Bottom left: Tutsan infestation, Wentworth Falls, NSW
Bottom right: ITS phylogeny of three Melampsora hypericorum isolates from Turton’s Creek, Havilah and Apollo Bay (RED) and other sequences from GenBank (including NCBI accession numbers), with bootstrap support values indicated at the nodes. Puccinia graminis is used as the outgroup (bold).
SEM images of the abaxial leaf surface of Hypericum androsaemum from Turton’s Creek, showing infection with Melampsora hypericorum (collected 30/03/2012). (a) Tutsan rust pustule; (b) collapsed, tutsan rust spores with wart-like projections within a rust pustule; (c) collapsed M. hypericorum spore with germ tube leading into stoma of H. androsaemum; (d) M. hypericorum germ tube leading into H. androsaemum stoma. Scale as indicated on each image. SEM images recorded on 14/05/12.