Hyalesthes obsoletus and bois noir

Bois noir phytoplasmosis was indicated since the beginning, for some infectivity features (nonepidemic), as a grapevine disease close but not identical to FD, because it is not transmissible by means of the leafhopper S. titanus Current knowledge confirms that BN is caused by a phytoplasma nonspecific for grapevine, transmitted by not strictly ampelo-phagous vector(s) Such an epidemiological situation, distinctly different from FD, reflects on the life cycle of the etiological agent of BN, involving different host plants, besides grapevine, and presumably different vectors, besides H. obsoletus, which is presently the only ascertained vector

BN is a long-known typical grapevine yellows in France and is widespread in different grapevine-growing areas of central and Mediterranean Europe, where it was called different names (Vergilbungskrankheit [VK] in Germany, and Legno Nero [LN] in Italy), and in the Middle East (Lessio et al , 2007) In the last few years this disease has constantly spread and stirred more and more concern for production and control The stolbur phytoplasma infects a high number of wild and cultivated plants, in particular vegetables . The disease was first described in central-eastern Europe as epidemic in Solanaceae, such as pepper, tomato, and eggplant Among wild plants this phytoplasma was found in arboreal and herbaceous hosts, many of which are commonly found in the vineyard agro-ecosystem

H. obsoletus is widespread in Europe, the Middle East, Asia Minor, and Afghanistan . H. obsoletus is a polyphagous and heterotopous species that accomplishes, in Europe, one generation per year and overwinters as a juvenile, mostly in the stage of third instar nymph, on the roots of different wild herbaceous plants, among which the most common ones are nettle (Urtica dioica) and convolvulus (Convolvolus arvensis), at a depth of about 100-150 mm (Alma et al ., 1988) . The adults are active in summer and feed occasionally on several herbaceous and shrubby broadleaf plants (Alma et al ., 1988; Sforza et al ., 1999; Sharon et al ., 2005). H. obsoletus may be found more frequently in the grapevine-growing areas where its herbaceous host plants, which are indispensable for egg laying and the development of juveniles, are spread . In these environments the adults feed on grapevine occasionally and for very short times, but enough, however, to inoculate BN, as it was proved also by means of laboratory trials (Lessio et al ., 2007) .

In spite of such evidence, the widespread and varying incidence of this ampelopathy, also in grapevine-growing areas where H. obsoletus was not found, and also the peculiar life cycle of the vector, with underground juveniles, lead to the hypothesis of the involvement of other wild plant hosts as natural infection sources of BN and of different vectors Concerning the role of other leafhoppers or planthoppers, commonly spread in the vineyard agro-ecosystem, serological and molecular investigations detected the stolbur phy-toplasma in many other species and a relevant interest assumes in particular its detection in species of the family Cixiidae, such as Reptalus panzeri (Palermo et al ., 2004), Reptalus quinquecostatus, Hyalesthes luteipes (Trivellone et al ., 2005), and Pentastiridius beieri (Gatineau et al ., 2001) . For all of them the role in checked transmission trials still has to be proved .

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