Genetic variability in phytoplasmas associated with papaya yellow crinkle and papaya mosaic diseases in Queensland and the Northern Territory

Samples of papaya (Carzca papaya L.) showing symptoms of papaya yellow crinkle (PYC) or papaya mosaic (PM) diseases were collected from two study sites in Queensland (Rockhampton and Caboolture) and from Katherine in the Northern Territory. Phytoplasmas were detected in these samples using polymerase chain reaction (PCR) and fluorescence microscopy techniques. The genetic variability of the phytoplasmas was studied using Southern blot hybridisation, restriction fragment length polymorphism (RFLP), and sequence analysis. RFLP analysis of PYC samples collected from Caboolture indicated that only the tomato big bud (TBB) type phytoplasma was present, whereas both PYC and PM samples collected from Rockhampton exhibited two phytoplasma types, sweet potato little leaf variant (SPLL-V4) and TBB. PYC samples collected from Katherine showed even greater variability with cactus witches’ broom (CWB), which was first described from Indonesia, detected in addition to SPLL-V4 and TBB which are common throughout Australia. Although PYC and PM diseases have different symptoms, no genetically distinct phytoplasma could be found in exclusive association with either disease