Proposal of A New Bois Noir Epidemiological Pattern Related to ‘Candidatus Phytoplasma Solani’ Strains Characterized by A Possible Moderate Virulence in Tuscany

Abstract

Bois noir (BN), associated with ‘Candidatus Phytoplasma solani’ (CaPsol), is the most widespread disease of the grapevine yellows complex worldwide. In this work, BN epidemiology was investigated in a case study vineyard where an unusual CaPsol strain, previously detected only in other host plants, was found to be prevalent in grapevine. Experimental activities included: symptom observation; sampling of symptomatic vines, Auchenorrhyncha specimens, and weeds; molecular detection and typing of CaPsol strains; statistical analyses for determining possible relationships between CaPsol relative concentration, strain type, and symptom severity. Among insects, Reptalus quinquecostatus was the most abundant and was found to be highly infected by CaPsol, while Hyalesthes obsoletus, the main CaPsol vector, was not caught. Moreover, R. quinquecostatus harbored CaPsol strains carrying uniquely the stamp sequence variant St10, also identified as prevalent in vines and in the majority of weeds, and all the secY variants identified in the vineyard. Statistical analyses revealed that CaPsol strains carrying the St10 variant are not associated with severe symptoms, suggesting their possible moderate virulence. Based on such evidence, a new BN epidemiological pattern related to these CaPsol strains and involving grapevine, R. quinquecostatus, and/or weeds is proposed. Furthermore, the possible presence of other players (vectors and weeds) involved in CaPsol transmission to grapevines was highlighted.

Multilocus Genotyping Reveals New Molecular Markers for Differentiating Distinct Genetic Lineages among “Candidatus Phytoplasma Solani” Strains Associated with Grapevine Bois Noir

“…These two patterns were identical to those previously reported for CaPsol tuf -type a and tuf -type b, respectively [ 3 ]. These results were consistent with previous findings of two tuf -types present in vineyards of northern [ 5 , 8 ], central [ 10 , 12 ], and southern [ 26 ] Italy. In the present work, CaPsol tuf -type a and tuf -type b were detected in 49.3% and 50.7% of the 142 symptomatic grapevine samples tested, respectively, but the two CaPsol tuf -types were differentially distributed ( Table 1 ).…”

“…Bois noir (BN), a grapevine disease associated with “ Candidatus Phytoplasma solani” (CaPsol) infection, causes typical grapevine yellows (GY) symptoms and results in important crop losses in the majority of vine-growing European countries, in the Middle East, and in South America [ 1 , 2 ]. Due to the involvement of multiple insect vectors and plant hosts, the biological cycle of CaPsol is extremely complex [ 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 ], hindering the development of control strategies for effective control of BN epidemics [ 11 ]. Molecular markers of genetic diversity among grapevine-affecting phytoplasmas set a solid foundation to improve knowledge of BN epidemiology.…”

“…In Europe, sequence analysis of translation elongation factor EF-Tu gene tufB revealed two main tuf -types of CaPsol ( tuf -type a and tuf -type b) present in diseased grapevines, as well as in alternative plant hosts nearby [ 3 ], suggesting that ecological differences could be associated with molecular diversification of CaPsol populations and their differential distributions. Numerous studies on molecular typing, based on anaylses of nucleotide sequences of more variable genes (e.g., secY , stamp , vmp1 ), showed large variability among CaPsol strain populations, shedding light on differences in virulence, origin, and host range of different strains [ 10 , 12 , 13 , 14 , 15 ]. Multiple gene typing analysis was applied to investigate genetic diversity in various bacterial taxa [ 16 , 17 , 18 , 19 ].…”

Symptomatology, (Co)occurrence and Differential Diagnostic PCR Identification of ‘Ca. Phytoplasma solani’ and ‘Ca. Phytoplasma convolvuli’ in Field Bindweed

“…P. solani’ infection in field bindweeds is far from elucidated. Plants can be either symptomatic or non-symptomatic while infected at similar rates and frequencies e.g., [ 3 , 6 , 10 , 12 , 14 , 18 , 21 , 22 , 23 , 24 ]. In our study, only at locality Kladovo symptomatic bindweed plants were infected solely with ‘ Ca.…”

“…Conversely, several more recent studies indicate that non-symptomatic plants of C. arvensis are a natural source of ‘ Ca. P. solani’ infection in agroecosystems [ 6 , 19 , 20 , 21 , 22 , 23 , 24 , 25 ]. Furthermore, the phytoplasma that is most closely related to ‘ Ca.…”