Research on grapevine yellows diseases in Piedmont, northern Italy: monitoring of diseases and vectors, typing of pathogens.

In 1998 a serious outbreak of Flavescence dorée (FD) was reported in Piedmont (north-western Italy). Despite insecticide treatments against the vector and roguing of infected plants since 1999, the average number of healthy grapevines has decreased and numbers of recovered plants and those with symptoms has increased. Molecular diagnosis has indicated the presence of FD and Bois Noir (BN) phytoplasmas in affected plants. A novel and quick diagnostic procedure based on RT-PCR was developed. The abundance of leafhopper Scaphoideus titanus Ball, vector of FD, in woodlands containing American grapevine, the occurrence of the planthopper Hyalesthes obsoletus Signoret, vector of BN on different host plants, and the presence in vineyards of other homopterans, suspected vectors of Grapevine yellows (GY) phytoplasmas, have been investigated to study the relationships between suitability of the ecosystem for development of insect vectors and the occurrence of GY. Field samplings included direct counting of nymphs of S. titanus, and inspection of roots of different plants for nymphs of H. obsoletus and other Cixiidae. Insects were analysed to detect GY phytoplasmas. A protocol for identification of molecular variability among BN isolates from grapevine, weeds and vectors has been developed.