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

Roberto Pierro,Marco Ginanni,Alessandro Passera,Augusto Loni,Andrea Lucchi,Andrea Luvisi,Alessandra Panattoni,Alberto Materazzi,Fabio Quaglino,Piero Attilio Bianco

doi:10.3390/pathogens9040268

Roberto Pierro, Marco Ginanni + Show 8 more

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https://doi.org/10.3390/pathogens9040268

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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.

Highlights

Grapevine yellows (GY) diseases, associated with phytoplasmas, constitute a major threat to viticulture worldwide
26 of these vines (54.2%) exhibiting severe symptoms were inserted in class 3; 12 of these vines (25%) exhibiting moderate symptoms were inserted in class 2; and 10 of these vines (20%) exhibiting mild symptoms were inserted in class 1 (Table 1)
Survey on grapevine yellows (GY) symptoms showed that the disease incidence (6.7%) in the vineyard in Greve in Chianti was stable in comparison with the previous year (7.2%), and confirmed the prevalence of diseased vines exhibiting severe symptoms (54.2% in 2017 vs. 47.2% in 2016)

Summary

Introduction

Grapevine yellows (GY) diseases, associated with phytoplasmas, constitute a major threat to viticulture worldwide. Bois noir (BN), one of the most important GY disease, is associated with. CaPsol largely spread in Europe, Mediterranean regions and Iran, and has been sporadically reported from China, Chile, and South Africa [1,2,3]. The cixiid Hyalesthes obsoletus Signoret, the main vector of BN [4], acquires CaPsol from its preferred host plants (Convolvulus arvensis L. and Urtica dioica L.), and occasionally transmits it to grapevine, a phytoplasma dead-end host [5,6]. Typing of CaPsol strains using different molecular markers improved the knowledge of BN spreading, highlighting the crucial role of Vitex agnus-castus L. and Crepis foetida L. as the main CaPsol source plants for H

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