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

We investigatedex situconservation options for two Australian rainforest species severely affected by myrtle rust in the wild - Rhodamnia rubescens(Benth.) Miq. andRhodomyrtus 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-1 sucrose, 1 mu m benzyl adenine and 0.2 mu m indole-3-butyric acid. Culture ofR. rubescensfor eight weeks on MS with 0, 5, 10 or 20 mu m 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% forR. rubescensand 0-75% forR. psidioides. ForR. rubescens, pretreatment of cuttings with Zaleton(R)and incubation in Preforma(R) plugs reduced the time to root development and significantly improved the strike rate (P = 0.001). R. rubescensseed proved to be orthodox and suitable for standard seedbanking;R. psidioidesseed proved to be freezing sensitive but suitable for storage at 4 degrees C. 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.