Conservation in the wake of myrtle rust – a case study on two critically endangered Australian rainforest plants

Abstract

We investigated ex situ conservation options for two Australian rainforest species severely affected by myrtle rust in the wild -Rhodamnia rubescens (Benth.) Miq. and Rhodomyrtus psidioides (G.Don) Benth. Both species were successfully initiated into tissue culture though the rate of contamination was high and not significantly improved by the disinfection techniques tested. Explants surviving initiation grew well on Murashige and Skoog medium (MS; pH 6.0) with 30 g L À1 sucrose, 1 mM benzyl adenine and 0.2 mM indole-3-butyric acid. Culture of R. rubescens for eight weeks on MS with 0, 5, 10 or 20 mM indole-3-butyric acid resulted in root production for some plantlets, and successful transfer to potting mix; no significant differences in root production among treatments were detected. Both species were successfully propagated by semi-hardwood cuttings with strike rates of 0-67% for R. rubescens and 0-75% for R. psidioides. For R. rubescens, pretreatment of cuttings with Zaleton Ò and incubation in Preforma Ò plugs reduced the time to root development and significantly improved the strike rate (P ¼ 0.001). R. rubescens seed proved to be orthodox and suitable for standard seedbanking; R. psidioides seed proved to be freezing sensitive but suitable for storage at 48C. As the two species now produce few viable seeds in the wild, however, conservation by seedbanking will first require the establishment of a seed orchard from vegetatively propagated plants. We recommend swift action to conserve species in the Pacific similarly affected by myrtle rust before their growth and reproductive capacity are seriously diminished.

Myrtaceae in Australia: Use of Cryobiotechnologies for the Conservation of a Significant Plant Family under Threat

“…Approximately 95% of the Myrtaceae are thought to have orthodox seed suitable for storage in a seedbank [72] and seedbanks in Australia currently hold collections for a total of 1534 taxa from 72 genera [73]. The remainder of the family falls into the category of 'exceptional' [74], with species that no longer produce seeds due to myrtle rust (e.g., Rhodamnia rubescens and Rhodomyrtus psidioides [70,75]), or that produce seeds that are intolerant of desiccation (e.g., Syzygium spp. [72,76]) or storage at −20 • C (e.g., Backhousia citriodora [77] and Rhodamnia maideniana [78]).…”

Plant Diversity Conservation Challenges and Prospects—The Perspective of Botanic Gardens and the Millennium Seed Bank

“…If the plants are not killed outright, the disease often affects the flowers and fruit and therefore collecting of seeds from the wild is usually not an option. The disease can be controlled in cultivation; however, progress of the disease may outpace germplasm capture for ex situ conservation such is the scale of the problem [76,100].…”

The Climate Change Alliance: botanic garden horticulturists as agents for change

“…Over 380 Australian taxa are potentially at risk from infection, with 43 severely affected (Makinson et al, 2020). The disease has impacted some relatively common species in their natural range so severely that two taxa (Rhodomyrtus psidii and Rhodamnia rubescens) are now listed as Critically Endangered (Makinson, 2018;Sommerville et al, 2020). In April 2013, myrtle rust was first detected at RBGV's Melbourne Gardens on Lophomyrtus obcordata (Fig.…”