A comparison of the phytoplasma associated with Australian grapevine yellows to other phytoplasmas in grapevine.
The phytoplasma associated with Australian grapevine yellows (AGY) was compared with other phytoplasma diseases of grapes using polymerase chain reaction (PCR) and restriction fragment length polymorphism (RFLP) analysis. Comparison of 8 different Australian isolates suggested that only 1 type of phytoplasma is associated with this disease. Based on RFLP analysis of the 16S rRNA gene, it was shown that AGY is different from the tomato big bud and sweet potato little leaf phytoplasma strains which are widespread in Australia and that it represents the only other phytoplasma strain recorded in Australia to date. Restriction profiles of grape phytoplasmas using MseI suggested that AGY is unique. It most closely resembled those phytoplasmas associated with grape diseases in the stolbur group. Sequence analysis of the 16S rRNA gene and adjacent spacer region supported this association. The uniqueness of AGY was confirmed by PCR assays using non-ribosomal primers; the primer pair STOL11fl/r2 specific for stolbur phytoplasmas did not result in amplification products in grapes affected by AGY; the primer pair fMLO1/rMLO1 which amplified a region of the tuf gene from phytoplasmas in the aster yellows cluster, amplified AGY DNA confirming its association within this phylogenetic group. RFLP analysis of the tuf PCR product highlighted a distinction between AGY and other stolbur phytoplasmas occurring in grapevine. The only other phytoplasma in Australia which is in the stolbur group is associated with dieback in pawpaws. It has the same RFLP profile of the tuf PCR product as AGY.