Prevalence of a ‘Candidatus Phytoplasma solani’ strain, so far associated only with other hosts, in Bois Noir‐affected grapevines within Tuscan vineyards

Abstract

Due to its complex epidemiological cycle, including several polyphagous insect vectors and 27 host plants, and the absence of efficient control strategies, Bois noir (BN) disease of grapevine is 28 encroaching wider territories in the main viticultural areas worldwide. Molecular approaches allowed to increase the knowledge about its etiological agent (Bois noir phytoplasma, BNp), 30 revealing interesting features concerning BNp population structure and dynamics and transmission 31 routes in vineyard agro-ecosystems. In the present study, a multi-locus sequence typing approach 32 (tufB, vmp1 and stamp genes) was utilized for describing the genetic diversity among BNp strain 33 populations in 17 vineyards localized in five districts of Tuscany (central Italy). The results 34confirmed that BNp ecology in Tuscan vineyards is mainly associated to the bindweed-related host 35 system, and allowed the identification of 13 collective BNp genotypes. Interestingly, the prevalent 36 BNp genotype was never found in grapevines outside of Tuscany. Moreover, statistical analyses 37 showed significant differences between the composition of BNp strain populations identified in 38 grapevines from distinct weather condition zones (north-western and central-eastern Tuscany). 39These results reinforce the hypothesis that environmental conditions can drive the selection of BNp 40 strains, also favouring the entrance of unusual genotypes, in vineyards.

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

“…Sequence identity analysis performed on 143 stamp gene amplicons allowed the identification of four sequence variants. Comparison with the stamp gene dataset, previously published in [13,14] and provided in Table S1, revealed that three of these sequence variants were identical to previously reported variants St5, St10, and St18; one variant, identified for the first time in this study and named St59, showed a similarity coefficient of 92.6% (35 SNPs) with St10. The nucleotide sequence of St59 was deposited in the NCBI GenBank repository under the Accession Number MN557212.…”

“…Molecular detection of GY phytoplasmas confirmed the absence of flavescence dorée (FD) in the examined vineyard. In order to investigate Bois noir (BN) epidemiology and possible differences in the phytoplasma virulence, 'Candidatus Phytoplasma solani' (CaPsol) strains identified in grapevine, insects and weeds were characterized by sequence analyses of variable genes stamp and secY, largely utilized in previous studies [20][21][22], and comparison with sequence variant datasets by Pierro and colleagues (Tables S1-S3) [13,14].…”

“…No amplification was obtained in negative controls. St10 − a , symbol "−": negative to amplification reaction; b ,CaPsol gene sequence variant determined by nucleotide sequence identity value versus sequence variants of the published datasets [13,14].…”

“…Recently, a CaPsol strain, previously detected only in other host plants and characterized by carrying stamp gene sequence variant St10, was found prevalent in BN-affected vineyards in the Chianti Classico area, Tuscany. Due to its widespread distribution and moderate virulence, it was hypothesized that this CaPsol strain coevolved in the Tuscan vineyard agroecosystem, adapting to grapevine and other hosts [13,14]. Interestingly, previous studies conducted in vineyards located in the same area revealed the abundant presence of the cixiid Reptalus quinquecostatus (Dufour) [15], found able to transmit CaPsol to feeding medium and to periwinkle and suspected to be a CaPsol vector to grapevine [16,17], and of spontaneous weeds largely infected by CaPsol [18].…”

Biochemical Changes in Leaves of Vitis vinifera cv. Sangiovese Infected by Bois Noir Phytoplasma

“…However, most studies focus on white-berried grape cultivars, which have different symptoms (yellow and chlorotic leaves) from red-berried grape cultivars (purple-reddish leaves).The aim of this study was to investigate the effect of BN disease on the primary and secondary metabolism parameters in leaves of a yet untested red-berried grape cv. Sangiovese, which is one of the most widespread Italian cultivars whose susceptibility to BN has been reported [22,23]. Specifically, the sugar accumulation, photosynthetic pigments and the compounds of phenylpropanoid pathways, such as phenolic compounds, flavonoids, proanthocyanidins, anthocyanins, and lignin, and their respective amounts were evaluated in BN-positive and BN-negative leaves, in two periods, according to symptom appearance (asymptomatic or symptomatic).…”