Phytoplasmas associated with papaya diseases in Australia

Leaf, petiole, and crown samples were taken from papaya with dieback or mosaic diseases, which have an unknown etiology, and from yellow crinkle disease, which has been associated with a phytoplasma. Using the polymerase chain reaction (PCR) and phytoplasma-specific primers, an amplification product of the expected size (1,076 bp) was observed in samples from papaya with yellow crinkle, mosaic, and dieback, and in none of the samples from asymptomatic plants. A second set of phytoplasma-specific primers was used with samples from each of the three diseases to produce a PCR product of 1,800 bp for restriction fragment length polymorphism (RFLP) analysis of phytoplasma relatedness. The phytoplasmas associated with yellow crinkle and mosaic were identical by RFLP analysis using three restriction enzymes, but the phytoplasma from dieback disease differed from the other two. The phytoplasma associated with dieback is related to the Stolbur phytoplasmas that form part of the aster yellows phytoplasma strain cluster. The phytoplasma associated with yellow crinkle and mosaic, along with sweet potato little leaf, appears to be related to a phytoplasma, crotalaria witches'-broom from Thailand, which in turn is related to the western X-phytoplasma.