Comparative studies of sequence motifs in the RNA polymerases and nucleic acid helicases of positive-sense RNA plant viruses have provided a new scheme for the classification of these pathogens. We propose a new luteovirus supergroup which should be added to the already described Sindbisvirus-like and picornavirus-like supergroups. Sequence motifs of nucleic acid helicases and RNA polymerases which previously were considered to be specific for each of the two supergroups now occur together within this new supergroup. We propose that this new viral supergroup provides an evolutionary link between the other two supergroups.

A phytoplasma was detected in naturally diseased 'Chardonnay' grapevines exhibiting symptoms of Australian grapevine yellows disease. The use of PCR designed to amplify phytoplasma DNA resulted in detection of phytoplasma DNA in all of the diseased plants examined; no phytoplasma DNA was detected in healthy seedling grapevines. The collective restriction fragment length polymorphism (RFLP) patterns of amplified 16s ribosomal DNA differed from the patterns described previously for other phytoplasmas. On the basis of the RFLP patterns, Australian grapevine yellows phytoplasma was classified as a representative of a new subgroup, designated subgroup 16SrI-J, in phytoplasma 16s rRNA group 16SrI (aster yellows and related phytoplasmas). A phylogenetic analysis in which parsimony of 16s rRNA gene sequences from this and other group 16SrI phytoplasmas was used identified the Australian grapevine yellows phytoplasma as a member of a distinct subclade (subclade xii) in the phytoplasma clade of the class Mollicutes. A phylogenetic tree constructed on the basis of 16s rRNA gene sequences was consistent with the hypothesis that there was divergent evolution of Australian grapevine yellows phytoplasma and its closet known relative, European stolbur phytoplasma (subgroup 16SrI-G), from a common ancestor. The unique properties of the DNA from the Australian grapevine yellows phytoplasma clearly establish that it represents a new taxon, "Candidatus Phytoplasma australiense."

An epidemic of grapevine leafroll disease (GLD), caused by grapevine leafroll-associated virus 3 (GLRaV-3), was monitored over an 11-year period in Nuriootpa, South Australia. Inoculum originated from infected budwood, and initial GLD incidence at the time of transplanting in 1986 was 23.1%. Infected vines were planted in a random spatial pattern. Change in disease incidence was not observed until 8 years after planting, when disease incidence increased to 27.9%. Disease incidence increased to 51.9% by 1996. Disease progress and rate curves (dy/dt versus time) indicated that the logistic (R2 = 96.2) and Gompertz (R2 = 96.3) growth models would best describe disease progress. However, the logistic model, which has a simpler data transformation with fewer model assumptions, was chosen for the purpose of comparing this epidemic (South Australia) with a GLRaV-3 epidemic in Cabernet Sauvignon grapevines in New Zealand. The logistic rate of GLD spread with respect to time was 0.35 logit/year in South Australia and was nearly three times faster (1.19 logits/year) for GLRaV-3 spread in New Zealand. Ordinary runs analyses indicated that the arrangement of infected vines within rows in South Australia was random up to 8 years after transplanting but subsequently became highly aggregated. Thus, GLD-infected plants are contributing to new infections (i.e., there is evidence for plant-to-plant spread), and a biotic vector with a steep dispersal gradient from each point source is likely to be involved.

Grapevine viruses are found throughout the viticultural world and have detrimental effects on vine productivity and grape and wine quality. This report provides a comprehensive and up-to-date review on grapevine viruses in Australia with a focus on “Shiraz Disease” (SD) and its two major associated viruses, grapevine virus A (GVA) and grapevine leafroll-associated virus 3 (GLRaV-3). Sensitive grapevine cultivars like Shiraz infected with GVA alone or with a co-infection of a leafroll virus, primarily GLRaV-3, show symptoms of SD leading to significant yield and quality reductions in Australia and in South Africa. Symptom descriptors for SD will be outlined and a phylogenetic tree will be presented indicating the SD-associated isolates of GVA in both countries belong to the same clade. Virus transmission, which occurs through infected propagation material, grafting, and naturally vectored by mealybugs and scale insects, will be discussed. Laboratory and field-based indexing will also be discussed along with management strategies including rogueing and replanting certified stock that decrease the incidence and spread of SD. Finally, we present several cases of SD incidence in South Australian vineyards and their effects on vine productivity. We conclude by offering strategies for virus detection and management that can be adopted by viticulturists. Novel technologies such as high throughput sequencing and remote sensing for virus detection will be outlined.