[T]he aster yellows (AY) phytoplasma group ... contains hundreds of known strains around the globe. The current taxonomic system assigns all the AY strains as ‘Ca. Phytoplasma asteris’-related strains, which grossly masks the differences among the strains ...

Plants infected by phytoplasmas often exhibit remarkable symptoms. These symptoms include virescence (flower petals turning green), phyllody (leafy flowers), cauliflower-like inflorescence (repetitive initiation of inflorescence meristems), and witches’-broom (excessive shoot proliferation). In addition to these characteristic symptoms, phytoplasma infection can also induce some general symptoms seen in diseases caused by various other plant pathogens. Such general symptoms include leaf discoloration (such as purple leaves and leaf yellowing), little leaf, stem fasciation, and stunting. Furthermore, asymptomatic phytoplasma infections were reported as well.