2014-2017

These projects were supported by the Australian Government as part of the National Environmental Research Program — Emerging priorities (Phase 1 project: 1 July 2014 to 1 May 2015) and the National Environmental Science Program — Emerging priorities (Phase 2 project: 15 May 2016 to 22 May 2017), administered by the Department of Environment and Energy (now Department of Agriculture, Water and the Environment).

Collaborator: Agriculture Victoria Research Division, Department of Jobs, Precincts and Regions (previously Department of Economic Development, Jobs, Transport and Resources)

Research performed by CSIRO focused on assessing the risk that the fungus Kordyana brasiliensis may pose to non-target native and ornamental plants closely related to wandering trad that are present in Australia. Additional host-specificity tests, to complement testing performed as part of the New Zealand program, were required because Australia has several native species in the Commelinaceae family to which wandering trad belongs to. Tests were undertaken in a quarantine facility in Australia.

Results obtained in these tests further demonstrated that K. brasiliensis is highly host specific towards wandering trad. All Australian populations of wandering trad tested were attacked by the fungus. Non-target plant species tested developed no symptoms or a limited number of small flecks on some leaves – an indication of resistance to infection by the fungus.

An application to release K. brasiliensis into Australia was submitted in November 2016 to the Department of Agriculture and Water Resources. Following a comprehensive risk assessment performed by the Department and consultation with states and territories as well as general public, the fungus was deemed to pose very low (negligible) risk to non-target plants and was approved for release from quarantine on 14 December 2018 (https://www.agriculture.gov.au/biosecurity/risk-analysis/memos/ba2018-32).

Disease symptoms caused by the fungus *Kordyana brasiliensis* on leaves of wandering trad under controlled conditions. Diffuse chlorotic spots on the upper surface of leaves (A) and corresponding whitish lesions on the under surface of leaves (B) at 14 days after inoculation. Lesions become necrotic as they mature (C), eventually causing complete necrosis and death of leaves (D).

As part of these projects, scientists from Agriculture Victoria Research Division also performed host-specificity tests with the Tradescantia leaf beetle, Neolema ogloblini in a quarantine facility to assess risks to non-target plants relevant for the Australian context.

In the Phase 1 project, choice-minus-target testing using leaf beetle adults was undertaken with 16 native and ornamental plants closely related to wandering trad. Oviposition and adult feeding damage by the leaf beetle were lower on the non-target species than on wandering trad, and none of the eggs hatched on any of the non-target plants.

In the Phase 2 project, a no-choice experiment was conducted by placing equal numbers of leaf beetle eggs onto the underside of wandering trad and the non-target species tested during Phase 1. Results showed that eggs hatched on all species and developed to adults on wandering trad and to various life-stages on seven of the Australian native Commelinaceae species tested: Aneilema acuminatum, A. biflorum, Murdannia graminea, Commelina ciliata, C. cyanea, C. diffusa and C. lanceolata. Higher numbers of individuals at all life-stages and more larval feeding damage (skeletonised leaves) were recorded on wandering trad.

Based on these results, a further no-choice adult oviposition experiment was set up using all test plants on which larval development had been recorded. After 3 months, only a single pupa was recovered from the cage containing A. acuminatum, confirming oviposition and development of the beetle to at least this stage on that species. With remaining resources in the project, one further experiment was undertaken to compare utilisation of A. acuminatum and wandering trad by the leaf beetle, by exposing plants to mating adult pairs within enclosed gauze sleeves. Results confirmed that the leaf beetle can oviposit on A. acuminatum but at rates nearly 20 times lower to those recorded on wandering trad. Furthermore, oviposition was only recorded on 2 of the 15 A. acuminatum replicate plants tested. After 14 days, numerous first and second instar larvae were present on wandering trad, but none were observed on A. acuminatum plants.

These experiments showed that the leaf beetle N. ogloblini is potentially not restricted in host range to wandering trad and may be able to develop on a few related Australian native plant species. Additional no-choice adult oviposition and developmental experiments performed over a longer period to allow multiple generations of the beetle to develop are required to fully assess risks before an application for release in Australia can be considered.