Abstract
Grapevine Bois noir (BN) is associated with infection by “Candidatus Phytoplasma solani” (CaPsol). In this study, an array of CaPsol strains was identified from 142 symptomatic grapevines in vineyards of northern, central, and southern Italy and North Macedonia. Molecular typing of the CaPsol strains was carried out by analysis of genes encoding 16S rRNA and translation elongation factor EF-Tu, as well as eight other previously uncharacterized genomic fragments. Strains of tuf-type a and b were found to be differentially distributed in the examined geographic regions in correlation with the prevalence of nettle and bindweed. Two sequence variants were identified in each of the four genomic segments harboring hlyC, cbiQ-glyA, trxA-truB-rsuA, and rplS-tyrS-csdB, respectively. Fifteen CaPsol lineages were identified based on distinct combinations of sequence variations within these genetic loci. Each CaPsol lineage exhibited a unique collective restriction fragment length polymorphism (RFLP) pattern and differed from each other in geographic distribution, probably in relation to the diverse ecological complexity of vineyards and their surroundings. This RFLP-based typing method could be a useful tool for investigating the ecology of CaPsol and the epidemiology of its associated diseases. Phylogenetic analyses highlighted that the sequence variants of the gene hlyC, which encodes a hemolysin III-like protein, separated into two clusters consistent with the separation of two distinct lineages on the basis of tufB gene sequences. Alignments of deduced full protein sequences of elongation factor-Tu (tufB gene) and hemolysin III-like protein (hlyC gene) revealed the presence of critical amino acid substitutions distinguishing CaPsol strains of tuf-type a and b. Findings from the present study provide new insights into the genetic diversity and ecology of CaPsol populations in vineyards.
Highlights
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]
Other plant pathogens [39], hemolysins act as virulence factors
The restriction fragment length polymorphism (RFLP)-based typing method used in the present study could be considered to be a valuable tool for research on the ecology of CaPsol and the epidemiology of its associated diseases
Summary
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]. 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. Multiple gene typing analysis was applied to investigate genetic diversity in various bacterial taxa [16,17,18,19] Such molecular typing was used to improve knowledge in phytoplasma classification [1,20,21,22,23] and improve knowledge of the epidemiology of phytoplasmal diseases [4,6,7,8,24]. The study identified new molecular markers useful for fine differentiation of CaPsol genetic lineages associated with different biological and geographic features
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