Potential for biological control of the weed Angled Onion (Allium triquetrum) by the fungus Stromatinia cepivora in Australia

The fungus Stromatinia cepivora (Berk.) Whetzel, which causes white rot of cultivated Allium species, was assessed as a biological control agent for Angled Onion (Allium triquetrum L.), a widespread noxious invasive environmental weed in southern Australia. A. triquetrum showed relatively little genetic diversity, suggesting it was a suitable target for biological control. Genetic analysis of plants from 23 sites in the three main infested Australian states by internal transcribed spacer (ITS) and randomly amplified polymorphic DNA (RAPD) analysis suggested biotypes of A. triquetrum in Australia grouped by state, except for samples from Westernport Bay and Ararat (Victoria). Pathogenicity and virulence of two S. cepivora isolates were assessed on up to 13 A. triquetrum provenances, 6 cultivated Allium species and 9 Australian endemic monocotyledons in test-tube and pot trials. In test-tubes, sclerotia killed plants from all provenances. In pot trials with sclerotia and mycelium, the more pathogenic isolate killed plants from all but one provenance. No A. triquetrum provenance was resistant to S. cepivora, nor were common cultivated Allium species, but common Australian endemic monocotyledons from habitats infested with A. triquetrum showed no disease symptoms 90 days post-inoculation. S. cepivora thus has potential as a biological control agent for A. triquetrum in native bushland in Australia where the risk of it spreading to horticulturally important Allium species is low and can be controlled.