"Candidatus Phytoplasma australiense" in Coprosma robusta in New Zealand

A phytoplasma is reported from wild plants of Coprosma robusta, where it is associated with leaf reddening or bronzing and dieback of shoots and branches. It was detected by electron microscopy of phloem tissue, and by one-step and nested PCR using phytoplasma-specific primers targeting the 16S rRNA gene. The sequence of the 16S product closely matches that of the Phormium yellow leaf phytoplasma and places the phytoplasma in the putative species "Candidatus Phytoplasma australiense". It was transmitted by grafting to C. robusta and C. macrocarpa. The symptoms of the disease caused by the phytoplasma (Coprosma lethal decline) in clonally matched graft-inoculated versus ungrafted cuttings of C. robusta included interveinal chlorosis and abnormal leaf yellowing or reddening, slowing of growth, and shoot dieback. A field survey of C. robusta indicated that shoot dieback and abnormal leaf coloration are common throughout much of New Zealand. "Ca. P. australiense" was detected in some, but not all, symptomatic plants, indicating it may play a role in causing such symptoms in the field. It is proposed that infected C. robusta plants provide a reservoir of "Ca. P. australiense" that leads to infection of other hosts.