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DISEASES ASSOCIATED WITH PHORMIUM YELLOW LEAF PHYTOPLASMA IN NEW ZEALAND

MT ANDERSEN1, LW LIEFTING1, J LONGMORE1, PW SUTHERLAND1, GA WOOD1, RE BEEVER2 and RLS FORSTER1

1HortResearch, Private Bag 92169, Auckland, New Zealand; 2Manaaki Whenua - LandCare Research, Private Bag 92170, Auckland, New Zealand

Background and objectives
Phytoplasmas are associated with over 600 diseases in more than 200 different plant species, and are spread by phloem-feeding leafhoppers or plant hoppers. The best characterized phytoplasma disease in New Zealand is Phormium yellow leaf (PYL). PYL was first described in NZ flax (Phormium spp.) in 1908, but was not determined to be a phytoplasma-associated disease until 1969. Although PYL contributed to the demise of the Phormium fibre industry in New Zealand, the disease was not considered a threat to other plant species as the vector responsible for transmission, Oliarus atkinsoni, is monophagous, and therefore not likely to spread the microoganism to other hosts. Until recently, PYL of NZ flax was thought to be the only significant phytoplasma disease in New Zealand. Since the early 1980s, however, a number of disorders have been reported in New Zealand with symptoms characteristic of phytoplasma-associated diseases, and for which no pathogen has been found. Such symptoms have appeared in plants as diverse as strawberry, boysenberry, and an indigenous icon, the New Zealand cabbage tree (Cordyline australis). Although each disease showed characteristics of being phytoplasma-associated disorders, each case varied considerably in symptoms and severity.

Results and conclusions
DNA extracted from symptomatic and non-symptomatic plants was tested using primers designed to 16S rRNA gene [1]. Nested PCR was used initially with two sets of universal phytoplasma primers to establish the presence of phytoplasma. Classification of detected phytoplasmas was then determined by use of group-specific primers and DNA sequence analysis. Phytoplasmas were detected in strawberries and cabbage trees displaying symptoms of a phytoplasma-like disorder. In all instances the phytoplasmas were determined to be PYL. Phytoplasmas were also detected in some, but not all, symptomatic boysenberries, but not in non-symptomatic plants. The phytoplasma detected was also PYL. A vector for transmission of PYL into strawberry, cabbage tree and boysenberry has not yet been identified.

References
1. Andersen MT, Beever RE, Gilman AC et al., 1998. Plant Pathology (in press).