Investigation on ‘bois noir’ epidemiology in north-eastern Italian vineyards through a multidisciplinary approach

A multidisciplinary approach, based on field surveys, molecular biology techniques, and spatial data analyses, was utilised to investigate the Bois noir (BN) epidemiology in north-eastern Italian vineyards during the years 2010–12. Symptomatic grapevines, weeds and specimens of the insect vector Hyalesthes obsoletus were monitored and mapped. Leaf samples from symptomatic grapevines and weeds, and captured insect specimens were analyzed by real-time PCR to identify BN phytoplasma (BNp; ‘Candidatus Phytoplasma solani’ species), the etiological agent of BN. Data spatial distribution was analyzed using SADIE (Spatial Analysis by Distance IndicEs). Bois noir phytoplasma strains identified in weed candidates for an epidemiological role were characterised by RFLP-based analyses of tuf gene amplicons. Results highlighted that, in the examined areas, the host systems Convolvulus arvensis – H. obsoletus and Urtica dioica – H. obsoletus play the main role in BN diffusion. It was also evidenced that other weeds (i.e. Chenopodium album and Malva sylvestris) spatially associated with symptomatic grapevines and/or insect vectors and infected by the same tuf type identified in grapevines and insects, could play a role in BN diffusion. On the other hand, some weeds (i.e. Trifolium repens) were uninfected and not associated with symptomatic grapevines and/or insect vectors. The synergic application of our multidisciplinary approach improved the knowledge of BN epidemiology, and provided helpful indication for designing experimental plans to contain BN spreading in vineyards through weed management. The approach described in the present work could be used to investigate the complex epidemiology of other phytoplasma diseases.