Hidden genetic diversity of ‘Candidatus Phytoplasma solani’ strains in Istrian vineyards: how small can be rich

Abstract

Grapevine Yellows (GY) are economically important diseases associated to phytoplasmas (genus ‘Candidatus Phytoplasma’), uncultivable bacteria from the class Mollicutes. In Euro-mediterranean region, GY are mainly attributed to phytoplasmas belonging to ribosomal 16SrXII-A subgroup ('Ca. P. solani'; Bois Noir phytoplasma; BNp) and 16SrV group (flavescence dorée phytoplasma; FDp), with the latter one being a quarantine pathogen (Plavec et al. 2015, Quaglino et al. 2013). Although symptomatology can be similar, epidemiology of FDp and BNp is very different as they are transmitted by different insect vectors and could have different alternative hosts. In Croatia, GY diseases have been continuously monitored since 1997 with FDp appearing only in 2009 (Šeruga Musić et al. 2011). While BNp is more diverse and widespread, FDp belonging to 3 map phylogenetic clusters are differently distributed throughout regions. Istria is heavily affected with FDp since 2014 with only one genotype (mapFD2/M54) being attributed to great losses (Plavec et al. 2019). On the contrary, information on BNp diversity is scarce with only couple of genotypes detected so far (Plavec et al, manuscript in preparation). Therefore, the aim of this case study was to assess the diversity of BNp genotypes in a small selected area of Istria, in order to draw attention to the presence and importance of BNp as GY agent in this important Croatian viticultural region.