Molecular tracing of the transmission routes of bois noir in Mediterranean vineyards of Montenegro and experimental evidence for the epidemiological role of Vitex agnus-castus (Lamiaceae) and associated Hyalesthes obsoletus (Cixiidae)

Abstract

Epidemiological aspects and transmission routes of bois noir (BN), a grapevine yellows disease induced by 'Candidatus Phytoplasma solani', have been exhaustively studied in the affected vineyards of continental Europe but not in the Mediterranean coastal zone. Because 'Ca. Phytoplasma solani' and its principal vector Hyalesthes obsoletus presumably originate from the Mediterranean, gaining knowledge of the epidemiological peculiarities of the disease in this area is essential for understanding its global spread and diversification, as well as for designing local management strategies. In this study, molecular epidemiology was applied to trace transmission pathways of 'Ca. Phytoplasma solani' in the Mediterranean vineyards of Montenegro, using multilocus sequence typing of tuf, vmp1 and stamp genes of the isolates associated with various hosts. Thus, 'Ca. Phytoplasma solani' was tracked from a tentative reservoir plant (inoculum source) through an associated vector population to the infected grapevine. Three pathways of transmission were documented, originating from Urtica dioica, Convolvulus arvensis and Vitex agnus-castus; however, only the route originating from U. dioica was direct, whereas the latter two were overlapping and could be intermixed. Vitex agnus-castus is a natural source of 'Ca. Phytoplasma solani', representing an important link in disease epidemiology in the Mediterranean and a possible origin of several genotypes occurring in central Europe. Experimental confirmation of the role of Vitex-associated H. obsoletus in BN transmission in Montenegrin vineyards indicates its tentative role as a vector in the wide area of the Mediterranean, where some of the major wine-producing regions are located.