An epidemiological study on a grapevine yellows disease called bois noir was carried out for 3 years in the Rhone valley (France). This yellows is caused by a stolbur type phytoplasma. Vectors and alternative host plants were searched, and the inoculation period was determined. Detection of stolbur phytoplasma in insects and plants was obtained using primers STOLl 1 f2,rl. In addition, a nested polymerase chain reaction (PCR) was used with primers P1/P7 and fU5/rU3 for detection in stolburinfected plants with low titre. Several thousand insects were captured and species of Hemiptera were listed. Fourteen wild or reared Hemiptera species were used in transmission trials. Thirty-four wild species were monitored for phytoplasma DNA by PCR. A planthopper.Hvalesthes obsoletus Sign., tested positive for stolbur at a level of 28% (98,/343) in 1995(98,/343) in and 38% (205,529) in 1996(98,/343) in . In 1995 leafhoppers, Mocydia crocea (1 78) and Euscelis tineolatus (2/309), were infected at a much lower ratio. Successful experimental transmission to grapevine, periwinkle and thorn apple was only obtained with H. obsoletus. Among wild plant species, hoary cress (Cardaria draba L.), bindweed (Convolvulus arvensis L.), sweet cherry {Prunus sp,), plum (Prunus domestica L), lilac (Syringa vulgaris L.), fig tree [Ficus carica L.) and elm {Ulmus sp.) were shown to be stolbur infected and hoary cress was identified as a new host plant for H. obsoletus in France. The role of some fallow lands close to vineyards as sites where the inoculum of stolbur phytoplasma was maintained in insect vector and reservoir plants, is discussed. The natural inoculation period to grapevine was shown to extend from June to August, corresponding to the adult activity of H. obsoletus. Together with the close relationships of the phytoplasmas involved in vergilbungskrankheit, a German grapevine disease, and bois noir. The results of this study suggest that the two yellows are very close. Zusammenfassung Bedeutung von Hyalesthes obsoletus (Hemiptera: Cixiidae) fur das Auftreten der Bois-noir-Krankheit der Weinrebe in Frankreich Im franzosischen Rhonetal wurde eine 3-jahrige epidemiologische Studie iiber die Bois-noir-Vergilbungskrankheit der Weinrebe durchgefuhrt. Diese Krankheit wird von einem Phytoplasma des Stolbur-Typs ausgelost. Es wurde nach Vektoren und alternativen Wirtspflanzen gesucht, und die Inokulationsperiode wurde bestimmt. Die Detektion von Stolbur-Phytoplasmen in insekten und Pftanzen erfolgte mit Hilfe der Primer STOL 1! f2/rl. Zudem wurde eine genestete PCR mit den Primem P1 /P7 und fU5 rU3 zur Detektion in stolburinfizierten Pflanzen mit niedrigem Titer durchgefuhrt. Mehrere tausend Insekten wurden gefangen, und die Hemiptera-Arten wurden aufgelistet. 14 wilde oder geziichtete HemipteraArten wurden in Ubertragungsversuchen verwendet, und 34 Wildarten wurden mittels PCR auf Phytoplasma-DNA untersucht. Der Fulgoride Hvalesthes obsoletus Sign, war 1995 mit 28% (98/343) und 1996 nut 38% (205/529) der getesteten Tiere stolburpositiv. ...

The syndrome "basses richesses" of sugar beet (SBR) was first observed in 1991 in Burgundy, France. A cixiid planthopper, Pentastiridius beieri, has been proved to be involved in the transmission to sugar beet of a stolbur phytoplasma, which could be detected in some affected plants. In 2000, periwinkle and sugar beet exposed to field-collected cixiids developed symptoms similar to SBR on sugar beet. Use of 4'-6-diamidino-2-phenylindole (DAPI) staining and transmission electron microscopy confirmed the presence of phytoplasma in some of the plants, which were also positive for this pathogen in a polymerase chain reaction (PCR) analysis. A phloem-restricted gram-negative bacteria was seen in all other plants with symptoms but PCR-negative for phytoplasma. Three primer pairs reported as diagnostic for phloem-limited bacteria were tested but only primers specific for 'Candidatus Phlomobacter fragariae' gave a positive signal, which related to the presence of DAPI-stained bacteria-like objects in diseased plants. Although phytoplasma and bacterium-like organisms were associated with the same macroscopic symptoms on sugar beet, histochemical analysis of phloem cells showed that phytoplasma were associated with cell necrosis and cell wall lignification, while bacteria were associated with these same abnormalities as well as deposit of phenolic compounds in the lumen of phloem cells.

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The incidence and transmissibility of Flavescence dorée phytoplasma (FDP) in populations of the vector Scaphoideus titanus Ball (Homoptera: Cicadellidae) were investigated by periodically collecting nymphs and adults of the leafhopper species in four vineyards with high incidence of Flavescence dorée (FD)‐diseased grapevines. Insects were tested individually for FDP with an ELISA procedure, after transmission assays to broadbean seedlings and further transmission to grapevine cuttings. No transmission occurred when early or middle instar nymphs were used to inoculate broadbeans, although a limited number of fifth‐instar nymphs and young adults transmitted the pathogen to broadbean seedlings. However, the same batches of insects transmitted FDP more efficiently to grapevine cuttings during prolonged inoculation periods, confirming the existence of a latent period before infected insects become infective. The proportions of ELISA‐positive individuals in the three categories of insects used for transmission assays reflected the rate of FDP transmission to grapevine cuttings. According to the data obtained by ELISA and from field sampling of first‐instar nymphs, we adapted the proportions of nymph hatching, of infected leafhoppers, and of infective leafhoppers (assuming a conservative latent period in the vector of 30 days) to logistic models as a function of degree‐days. We then discussed the possible use of the model developed for improving vector control decisions in FD‐infected vineyards.