Epidemiological surveys were performed in Northern Sardinia (Italy) in a 10-year-old vineyard affected by “Bois noir” disease. Samples collected between May and October 2003 from chlorotic and stunted weeds belonging to 14 different taxonomic groups were indexed molecularly for detection of phytoplasmas. Nested polymerase chain reaction (PCR) assays using primers specific for the phytoplasma 16SrDNA gene showed three of six Calendula arvensis, one of two Solanum nigrum, and one of seven Chenopodium spp. assayed positive. Restriction fragment length polymorphism analyses and sequencing of amplified 16SrDNA fragments identified a putative phytoplasma in the ribosomal subgroup 16SrII-E. Further characterization of the rps3 gene, coding a ribosomal protein, confirmed the identification. However, the weeds and leafhop-per species collected in the vineyard tested negative by PCR assays for the Stolbur phytoplasma, the causal agent of “Bois noir”. This is the first report of a phytoplasma of the 16SrII-E subgroup infecting C. arvensis, S. nigrum, and Chenopodium spp.
An unusual disorder occurred on ‘Vernaccia’ vine, particularly in the typical cultivation area of the variety, in the province of Oristano. Main symptom is the decaying of wood and bark. This causes the loss of the bark on the circumference of the trunk and causes the plants to die. Degradation can develop very deep in the wood rings. Affected rings can detach from the new formed ones.
The infectious process is very serious in the younger plants and can slow their evolution in the years. Furthermore it does not allow the recovery of the affected plants. In some vineyards 4 % of affected plants occur. Mortality can reach up to 20%, of the affected plants and is very high during the early years after infection.
A bacterium has been constantly isolated from decaying tissues; for its morphological and physiological characters and the response to serological tests it has been included in the Pseudomonas syringae Van Hall group. Pathogenicity tests carried out on ‘Vernaccia’ vines and other varieties resulted always positive; the bacterium has always been reisolated from artificially affected areas. The latter were much diffused and, sometimes, reproduced the typical symptomatology of the disease observed in nature.
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