Molecular and spatial analyses reveal new insights on Bois noir epidemiology in Franciacorta vineyards

Bois noir (BN) grapevine disease is associated with ‘Candidatus Phytoplasma solani’ (CaPsol), a pathogen with a complex ecology including multiple insect vectors and plant hosts. A key point to improve the effectiveness of BN control strategies consists in determining the epidemiological role of ground-cover weeds. The present study employed a multidisciplinary approach, based on the application of spatial (spatial analysis by distance indices) and molecular (stamp gene typing) analyses, to identify weeds with a potential role in BN epidemiology in northern Italy. Generated data showed that in addition to Convolvulus arvensis, one of the main CaPsol inoculum sources, Chenopodium album, Polygonum aviculare and Trifolium repens were found associated with BN epidemiology. CaPsol molecular typing highlighted that the strains prevalent in symptomatic grapevines were characterised by stamp sequence variants St19, St11 (nettle-related) and St5 (bindweed-related). The latter was prevalent also in Hyalesthes obsoletus and weeds, suggesting their main association with bindweed-related epidemiology. On the other hand, nettle-related CaPsol strains were occasionally found in H. obsoletus and weeds. Considering that H. obsoletus-mediated transmission of CaPsol occurs mainly with young instars, further investigations will confirm if, in addition to bindweed and nettle, weeds associated with BN epidemiology in Franciacorta can represent larval developmental hosts and, consequently, act as CaPsol reservoirs for transmission to grapevine. Moreover, other studies are needed to clarify the relationship between such weeds and CaPsol alternative vectors.