Phytoplasma diseases in sub-tropical and tropical Australia

Phytoplasmas are phloem-limited plant pathogens that have been identified in over 1000 plant species worldwide. Outbreaks of the phytoplasma-related disease, papaya dieback, has resulted in 10 - 100% crop losses in south-east Queensland and Western Australia. Strawberry lethal yellows and green petal disease outbreaks in Queensland have led to 10 - 50% of strawberry runners being destroyed. Lucerne yellows disease has been reported to cause an annual loss of AU$ 7 million to the lucerne seed industry. Disease surveys in Australia have increased our understanding of phytoplasma diseases in Australia and these fastidious organisms have been detected in similar to 70 native and introduced plant species. The majority of the Australian phytoplasmas are assigned to the 16SrII group, however, a member of the 16SrXII group is more commonly associated with economically important diseases in Australia such as strawberry lethal yellows, papaya dieback and grapevine yellows. These phytoplasma diseases have been diagnosed using PCR primers specific for their 16S rRNA gene. Screening hundreds of samples using PCR is time consuming and expensive so current and future studies are characterising an Australian phytoplasma genome and identifying suitable targets for the development of a more rapid diagnostic test for phytoplasmas.