Stylosanthes is a Host for Several Phytoplasmas, One of which Shows Unique 16S-23S Intergenic Spacer Region Heterogeneity

Stylosanthes sp. exhibiting characteristic symptoms such as little leaf, witches' broom and floral abnormalities were collected from north Queensland and the Northern Territory, Australia. Previous studies have shown that sweet potato little leaf V4 (SPLL-V4), tomato big bud (TBB), stylosanthes little leaf (StLL) and pigeon pea little leaf (PLL) phytoplasmas are associated with this disease. The detection of an additional phytoplasma type, vigna little leaf (ViLL) is reported herein. The range and severity of symptoms expressed by affected plants is highly variable and is not associated with a particular phytoplasma type. Similarly, host plants infected with a complex of two phytoplasmas did not have unique or more severe symptoms. Of the phytoplasmas associated with stylosanthes little leaf disease, StLL is unique because it lacks the tRNA^Ile gene which is normally situated in the 16S-23S rRNA intergenic spacer region. This phytoplasma was shown to have a second operon containing the expected tRNA^Ile gene in all StLL samples examined. Sequence analysis suggests that the two 16S rRNA genes amplified by polymerase chain reaction from StLL samples originate from the same phytoplasma. This the first report of a phytoplasma having ribosomal operons both with and without an intergenic tRNA^Ile gene.