Biological control of the invasive plant Tradescantia fluminensis with the fungus Kordyana brasiliensis in Australia: Host range and initial releases

Abstract

The herbaceous groundcover plant Tradescantia fluminensis (wandering trad) has become a significant invader of temperate and subtropical forest ecosystems in Australia. Classical biological control (biocontrol) offers a sustainable and broad-scale management strategy to reduce wandering trad populations. The leaf-smut fungus Kordyana brasiliensis from Brazil, investigated as part of the New Zealand biocontrol program for wandering trad, was identified as a promising option for biocontrol in Australia. Additional research, however, was required to investigate further the host range of K. brasiliensis and fully assess risks since several native species in the family Commelinaceae are present in Australia. Kordyana brasiliensis only developed lesions on the 14 different accessions of wandering trad tested. Of the 28 non-target plant taxa tested, 5 developed flecks following inoculation with K. brasiliensis. In 2019, initial releases were performed in two regions, the Shoalhaven in New South Wales and Dandenong Ranges in Victoria, to obtain contrasting information on the development of the fungus post-release. Kordyana brasiliensis lesions were detected on wandering trad at the 4 plots in the Shoalhaven within a couple of months of the release. In contrast, a few lesions were detected only 5 months after the release at a few of the 9 plots in the Dandenong Ranges. Cooler temperatures in the Dandenong Ranges may have hampered development of the fungus. After 26–32 months of those initial releases, wandering trad foliage cover had declined substantially in 3 of the 4 plots in the Shoalhaven but had remained stable in the Dandenong Ranges plots. While the reduction in wandering trad cover may have resulted from recurrent disease caused by K. brasiliensis at the Shoalhaven plots, a longer post-release monitoring period is required to support this conjecture with greater certainty.