Epidemiology of Phytoplasma-Associated Papaya Diseases in Queensland, Australia.

Three phytoplasma-related diseases of papaya (Carica papaya), dieback, yellow crinkle, and mosaic, are recognized within Australia. Immature leaf material was sampled every week for 8 months from a cohort of 60 female plants, located within a commercial papaya plantation, to determine the minimum time between infection and symptom expression. Phytoplasma DNA was detected using the polymerase chain reaction (PCR) with primers specific for phytoplasmas in general, and for the stolbur group of phytoplasmas. The dieback-associated phytoplasma was detected 1 week prior to (four cases) or the same week (nine cases) as symptom expression, while phytoplasma DNA was detected between 3 and 11 weeks prior to expression of mosaic symptom (six cases). Lateral shoot regrowth on the lower stem of plants which had suffered dieback disease failed to generate stolbur-specific PCR products in 15 cases. A dual infection with dieback and yellow crinkle or mosaic was diagnosed in a further two cases, using restriction fragment length polymorphism digests, and both cases were interpreted as secondary infections by the dieback-associated phytoplasma. Regrowth in three of seven cases of yellow crinkle- and three of nine cases of mosaic-affected plants tested positive for phytoplasma-specific DNA. Ratooning of dieback-affected plants and removal of yellow crinkle- or mosaic-affected plants is suggested for the management of these diseases.