Association of "Candidatus phytoplasma australiense" with sudden decline of cabbage tree in New Zealand

Sudden decline of the New Zealand cabbage tree (Cordyline australis) result s in the rapid death of affected plants within months of first external sym ptoms becoming apparent. Symptoms, which have been observed in saplings and mature trees, include vascular discoloration and leaf yellowing followed b y leaf desiccation and eventual plant collapse. Previous work failed to lin k the disease with any causal agent. A phytoplasma has now been detected in all symptomatic saplings and some symptomatic trees tested, using one-step and nested polymerase chain reaction (PCR) to amplify portions of the 16S rRNA gene. This phytoplasma was not detected in nonsymptomatic plants. Phyt oplasma DNA was found in shoot and rhizome apices, leaves and wood tissue o f saplings, and in the rhizome apex and trunk tissues of adult trees. Seque ncing of the PCR products from selected samples indicated that the phytopla sma is "Candidatus Phytoplasma australiense." Phytoplasma cells were detect ed by transmission electron microscopy in phloem sieve tubes of the rhizome s of affected saplings. One sapling with early symptoms recovered after inj ection with tetracycline antibiotic, but two saplings with advanced symptom s did not recover. It is concluded that "Candidatus Phytoplasma australiens e" is present in symptomatic plants and is the cause of sudden decline.