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 to other phytoplasma diseases of grapevine using the polymerase chain reaction (PCR) and restriction fragment length polymorphism (RFLP) analysis. Comparison of eight different Australian isolates suggests that only one 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 grapevine phytoplasmas using Mse I suggest that AGY is unique but most closely resembles those phytoplasmas associated with grapevine diseases in the stolbur group. Sequence analysis of the 16S rRNA gene and adjacent spacer region supports this association. The uniqueness of AGY was confirmed by PCR assays using non-ribosomal primers; the primer pair STOL11f/r2 specific for stolbur phytoplasmas did not result in amplification products in grapevines affected with AGY; the primer pair fMLOl/rMLOl which amplifies 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 tufPCR product again 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 papaya, and it has the same RFLP profile of the tuf PCR product as AGY.