SUSTAINABLE INTEGRATED MANAGEMENT OF GRAPEVINE BOIS NOIR AND ITS ASSOCIATED INSECT VECTORS

Bois Noir (BN) is a disease of the grapevine yellows (GY) complex associated with ‘Candidatus Phytoplasma solani’ (CaPsol) strains, which causes economic crop losses in viticulture worldwide. The epidemiology of BN is very complex due to the involvement of different herbaceous plants and several insect vectors that transmit CaPsol to grapevine. Therefore, the BN containment is very difficult and require massive efforts for possible spread reduction. The heavy application of chemical insecticides was not successful to control the insect vector presence within the vineyard. The thesis work was framed considering the directives provided by the European council 2009/128/EC regarding the promotion of low use of pesticides in sustainable management approaches. In the present thesis dissertation, CaPsol insect vectors and diseased grapevines were the main targets prioritized for successful containment of BN in organically cultivated vineyards in northern Italy. Since H. obsoletus is the widely distributed insect vector in Europe, the management of the leafhopper population was carefully considered. The use of Vitex agnus-castus as trap plant for H. obsoletus as an indirect control strategy was evaluated. Vitex agnus-castus tended to be a preferred host plant for H. obsoletus, but transmission trials demonstrated its ability to harbor CaPsol and indicated the impossibility of using this plant to avoid BN spread. In addition, the efficacy of different entomopathogenic nematodes and fungi as direct control strategy were evaluated against H. obsoletus nymphs and adults. Their application in a laboratory and semi-field conditions showed a promising killing effect that can be implemented for insect vector control in open field. Due to the very low density of H. obsoletus population in heavily BN infected vineyards questions were raised to figure out the other possible presence of alternative insect vectors. Surveys on Auchenorrhyncha coupled with molecular analyses revealed the presence of numerous putative vectors. Some of them, selected on the basis of their abundance, CaPsol-infection rate and CaPsol strains harbored, went through transmission trials. Eight insects were found able to transmit CaPsol to grapevines. Characterization of the bacterial microbiota associated with H. obsoletus and the alternative insect vectors indicated an interesting perspective regarding the microbial signatures associated with xylem- and phloem-feeding insects, and determinants that could be relevant to establish whether an insect species can be a vector or not, opening up new avenues for developing microbial resource management-based approaches. Moreover, grafting of materials collected from recovered grapevines was conducted in field trials with the aim to evaluate its preventive and curative potentials against BN. Results of symptom observation and CaPsol molecular detection on grafted and non-grafted grapevines showed that grafting of recovered shoots can have a curative effect, increasing the natural recovery. Results obtained in this PhD thesis opened new perspectives to develop integrated sustainable strategies for BN management.