The first steps towards investigating the molecular epidemiology of Stylosanthes little leaf phytoplasma in Australia

Abstract

Stylosanthes little leaf (StLL) phytoplasmas were first identified from two Fabaceae plant species in Queensland Australia in 1999. More recently, StLL was detected in a potato crop in Victoria, southern Australia, with a small percentage (<1%) of plants showing stunted and deformed growth, including little leaf symptoms. StLL had not been previously detected in potato or in this region of Australia. The 16S rRNA gene of StLL in potatoes was 99.2% identical to the rRNA gene sequence of the 1999 Queensland strain. Phylogenetic analyses of this gene shows that StLL from potato samples shares the highest sequence homology with ‘Candidatus Phytoplasma malaysianum’ (16SrXXXII-A; 97.2%). Phylogenetic analyses that incorporated representative ‘Ca. Phytoplasma’ taxa as well as StLL 16S rDNA sequences showed that all the StLL strains form a wellsupported cluster away from the other phytoplasma taxa. Nucleotide and phylogenetic analyses of genes more variable than 16S rRNA, such as secA, secY, tuf and rp, are being investigated for their suitability as molecular markers for subgrouping within StLL samples. The results may allow for the proposal of a new phytoplasma taxon and to test the usefulness of various genes in subgrouping these phytoplasmas. Importantly, the results may provide a better understanding of the epidemiology of StLL disease in Australia.