Publications

4501

Wheat blue dwarf (WBD) is one of the most economically damaging cereal crop diseases in northwestern PR China. The agent associated with the WBD disease is a phytoplasma affiliated with the aster yellows (AY) group, subgroup C (16SrI-C). Since phytoplasma strains within the AY group are ecologically and genetically diverse, it has been conceived that the AY phytoplasma group may consist of more than one species. This communication presents evidence to demonstrate that, while each of the two 16 rRNA genes of the WBD phytoplasma shares >97.5 % sequence similarity with that of the ‘CandidatusPhytoplasma asteris’ reference strain, the WBD phytoplasma clearly represents an ecologically separated lineage: the WBD phytoplasma not only has its unique transmitting vector (Psammotettix striatus) but also elicits a distinctive symptom in its predominant plant host (wheat). In addition, the WBD phytoplasma possesses molecular characteristics that further manifest its significant divergence from ‘Ca. P. asteris’. Such molecular characteristics include lineage-specific antigenic membrane proteins and a lower than 95 % genome-wide average nucleotide identity score with ‘Ca. P. asteris’. These ecological, molecular and genomic evidences justify the recognition of the WBD phytoplasma as a novel taxon, ‘CandidatusPhytoplasma tritici’.

"Candidatus Liberibacter solanacearum" is a gram-negative, fastidious bacterium that inhabits and multiplies in the phloem of host plants. The bacterium causes economically important diseases of solanaceous crops such as "zebra chips" of potatoes, and chlorotic weakening of cultivated plants of the Apiaceae family. Beside potatotes, this pathogen causes significant economic losses in tobacco, peper and tomato production. Insect vectors classified in the family Triozidae play an important role in the epidemiology of this bacterium. Insects transfer bacterial cells from infected to healthy plants by feeding on the plant juice from the phloem tissue. This pathogenic bacterium could be transmitted by infected seeds which result in long-distance spread. Based on the analysis of single nucleotide polymorphism (SNP), nine haplotypes (A, B, C, D, E, F, G, H, U) from different geographical regions, host plants and insect vectors have been described. Considering to impossibility of isolation of this bacterium on a nutrient medium, detection and identification are based on the application of molecular methods (conventional PCR, real-time PCR, multiplex PCR, nested PCR and LAMP PCR). Taking into consideration the increasing spread of "Candidatus Liberibacter solanacearum" in Europe, as well as its recent detection in Serbia, the aim of this paper was to raise an awareness about importance of this bacterium and summarize the protocols and molecular methods for its detection and identification.

‘Candidatus Liberibacter asiaticus’, an unculturable α-proteobacterium, is associated with citrus huanglongbing (HLB), a devastating disease threatening citrus production in Brazil and worldwide. In this study, a draft whole-genome sequence of ‘Ca. L. asiaticus’ strain 9PA from a sweet orange (cultivar Pera) tree collected in São Paulo State, Brazil, is reported. The 9PA genome is 1,231,881 bp, including two prophages, with G+C content of 36.7%. This is the first report of a whole-genome sequence of ‘Ca. L. asiaticus’ from Brazil or South America. The 9PA genome sequence will enrich ‘Ca. L. asiaticus’ genome resources and facilitate HLB research and control in Brazil and the world.

Abstract Phy.to.plas‐ma. Gr. masc. n. phytos a plant; N.L. neut. n. Phytoplasma a form from a plant. Phytoplasmas are wall‐less, nutritionally fastidious, and phytopathogenic prokaryotes 0.2–0.8 μm in diameter that morphologically resemble nonhelical members of the class Mollicutes . Sequencing of nearly full‐length PCR‐amplified 16S rRNA genes, combined with earlier studies, provided the first comprehensive phylogeny of the organisms and showed that they constitute a unique, monophyletic clade within the Mollicutes . These organisms are most closely related to members of the genus Acholeplasma within the Anaeroplasma clade as defined by Weisburg et al. Despite decades of efforts and recent progress, sustained pure culture in cell‐free media has not yet been demonstrated for any phytoplasma. Their genome sizes have been estimated to range from 530 to 1,350 kb, and the DNA G + C content is about 23–30 mol%. The presence of a characteristic oligonucleotide sequence in the 16S rRNA gene, CAA GAY BAT KAT GTK TAG CYG GDC T, and standard codon usage indicate that phytoplasmas represent a distinct genus‐level taxon for which the name ‘ Candidatus Phytoplasma’ has been adopted. At present, for any subtaxa within the provisional genus, the designation ‘ Candidatus ’ must still be used. DNA G + C content (mol%) : 23–29. Taxonomic and Nomenclature Notes According to the List of Prokaryotic names with Standing in Nomenclature (LPSN), the taxonomic status of the genus Candidatus Phytoplasma is: preferred name (not correct name) (last update, February 2025) * . LPSN classification: Bacteria / Bacillati / Mycoplasmatota / Mollicutes / Acholeplasmatales / Acholeplasmataceae / Candidatus Phytoplasma Candidatus Phytoplasma could not be recovered in GTDB ** . * Meier‐Kolthoff et al. ( 2022 ). Nucleic Acids Res , 50 , D801 – D807 ; DOI: 10.1093/nar/gkab902 ** Parks et al. ( 2022 ). Nucleic Acids Res , 50 , D785 – D794 ; DOI: 10.1093/nar/gkab776