Peach witches’-broom, an emerging disease associated with ‘Candidatus Phytoplasma phoenicium’ and ‘Candidatus Phytoplasma aurantifolia’ in Iran

During field surveys carried out from 2013 to 2017 in the eight main peach producing provinces of Iran, symptoms of a phytoplasma-like peach witches'-broom disease (PWIB), inducing severe yellowing, little leaf, internode shortening, crown and stem witches\u2019-broom, decline, and death, were observed. The aim of this work was to identify and characterize the agent(s) associated with PWIB by biological assays and molecular analyses. PWIB agents were successfully transmitted under controlled conditions from scions of in field-affected peach trees, exhibiting severe or mild symptoms, to peach and bitter almond seedlings inducing phytoplasma-like symptoms. A 16S rDNA fragment of 1250 bp was amplified by nested-PCR from all PWIB-affected trees and grafted seedlings. Nucleotide sequence identity, presence of species-specific signature sequences, in silico RFLP, single nucleotide polymorphisms, and phylogenetic analyses of 16S rDNA allowed the assignation of the phytoplasma strains identified in seven Iranian provinces in peach trees with severe PWIB symptoms to four SNP genetic lineages of \u2018Ca. P. phoenicium\u2019 (subgroup 16SrIX-B and its variant). PWIB phytoplasma strains identified in Abarkooh (Yazd province) in peach trees with mild symptoms were attributed to the species \u2018Ca. P. aurantifolia\u2019 (subgroup 16SrII-C). This report of a wide spread of \u2018Ca. P. phoenicium\u2019 in association with PWIB in Iran supported its capability of adaptation to a broad range of fruit tree species, such as peach, nectarine, and apricot. As \u2018Ca. P. phoenicium\u2019 and \u2018Ca. P. aurantifolia\u2019 are the etiological agents of other important plant diseases in Iran and neighbouring countries, further investigations are needed to determine the role played by peach in their epidemiological pathways

Development Of A New Probe For Specific And Sensitive Detection Of 'Candidatus Phytoplasma Mali' In Inoculated Apple Trees

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Activity of synthetic and natural compounds for phytoplasma control

A sustainable and rational procedure to evaluate the activity of synthetic and natural substances towards phytoplasma agents of important tree diseases was developed with the aim of finding new strategies of control. The method of testing is based on 1) the utilization of Catharanthus roseus; 2) the artificial infection of periwinkles with two phytoplasma strains; 3) scion dipping, selected as the most suitable method of applying the substances. A series of natural and synthetic compounds were chosen among a) new agrochemical entries, registered as plant-resistance inducers; b) secondary metabolites of fungal and plant origin; c) new and known biologically active substances never tested before for their antiphytoplasmal properties. The activity of this series of compounds on healthy and phytoplasma-infected periwinkles was evaluated on the basis of several parameters: phytotoxicity, evolution of symptoms and microscope observations. The in-volvement of the third component in the triangular interaction between phytoplasma, plant and compound is discussed

Apricot yellows associated with ‘Candidatus Phytoplasma phoenicium’ in Iran

Almond witches\u2019 broom associated with \u2018Candidatus Phytoplasma phoenicium\u2019 is an economically important disease of almond in Iran and Lebanon. During surveys of almond witches\u2019 broom in 2012\u20132015, an apricot yellows disease was observed in Fars Province of Iran. The characteristic symptoms of the disease were leaf yellowing, inward leaf curl, scorch of leaf margins, shortened internodes, production of rosettes at the tips of the branches, and decline, stunting, and death of affected trees. Healthy bitter almond and apricot seedlings, grafted with shoots from symptomatic trees, exhibited phytoplasma-type symptoms. A 16S rDNA fragment of 1,250 bp was amplified by nested-PCR from affected trees and grafted seedlings. Nucleotide sequence identity, presence of species-specific signature sequences, and phylogenetic analysis of 16S rDNA allowed the assignation of the phytoplasma strains identified to the \u2018Ca. P. phoenicium\u2019. In vitro and in silico RFLP analyses of the amplified fragment allowed affiliation of the apricot yellows phytoplasma to a molecular variant in the subgroup 16SrIX-B. Within the population strains identified in this and previous studies, 16 genetic lineages were determined within 16S rDNA nucleotide sequences by the combination of 19 single nucleotide polymorphisms. The apricot yellows phytoplasma strains belong to a unique genetic lineage distinguished by the presence of three lineage-specific SNPs. This first report of \u2018Ca. P. phoenicium\u2019 in association with apricot yellows in Iran opens new perspectives on the epidemiology of almond witches\u2019 broom, suggesting possible adaptation of the phytoplasma to other fruit tree species

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

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

Curtobacterium sp. genome sequencing underlines plant growth promotion-related traits

Endophytic bacteria are microorganisms residing in plant tissues without causing disease symptoms. Here, we provide the high-quality genome sequence of Curtobacterium sp. strain S6, isolated from grapevine plant. The genome assembly contains 2,759,404 bp in 13 contigs and 2,456 predicted genes

New insights on Flavescence dorée phytoplasma ecology in the vineyard agro-ecosystem in southern Switzerland

Phytoplasmas associated with Flavescence dor\ue9e (FDp) grapevine disease are quarantine pathogens controlled through mandatory measures including the prompt eradication and destruction of diseased plants, and the insecticide treatments against the insect vector, the ampelophagous leafhopper Scaphoideus titanus. In the present study, a multidisciplinary approach has been applied to investigate the FDp ecological cycle in a test vineyard agro-ecosystem in Canton Ticino, south Switzerland. Despite the scarce population density of S. titanus, a regular trend of new infections (3.4% of the total vines) through the years was observed. The leafhopper Orientus ishidae was found as the most abundant among the captured insect species known as phytoplasma vectors (245 out of 315 specimens). The population of O. ishidae was evidenced prevalently (167 specimens) in the south-western side of the vineyard and within the neighbouring forest constituted mainly by hazel (Corylus avellana) and willow (Salix spp.). These plant species were found infected by FDp related strains (30% of analysed trees) for the first time in this study. Interestingly, O. ishidae was found to harbour FDp related strains in high percentage (26% of the analysed pools). In addition, 16SrV phytoplasma group was detected for the first time in the insect Hyalesthes obsoletus and a FDp related strain in Thamnotettix dilutior, present in low populations within the test vineyard. Molecular characterisation and phylogenetic analyses of methionine aminopeptidase (map) gene sequences of FDp and related strains, here identified, revealed the great prevalence of the map-type FD2 in grapevines (97%) and in O. ishidae pools (72%). Such a map-type was found also in hazel and in T. dilutior, but not in S. titanus. Moreover, map-types FD1 and FD3 were identified for the first time in Switzerland in several host plants and phytoplasma vectors, including grapevine (FD1), S. titanus (FD1) and O. ishidae (FD1 and FD3). Based on the data obtained in this study, it is reasonable to hypothesise that the ecological cycle of FDp could be related not exclusively to the grapevine-specific feeding diet of S. titanus, but it could include other insect vector(s) and/or plant host(s). Further studies will be needed to prove the role of O. ishidae as vector able to transmit FDp from wild plants (e.g. hazel) to grapevine

Comparative fruit quality parameters of ‘Ninfa’ apricot (Prunus armeniaca L.) grafted on two different rootstocks in a newly established organic orchard

The fruit quality parameters of Prunus armeniaca L. cv ‘Ninfa’ grafted on ‘Myrobalan 29C’ (Prunus cerasifera Ehrh.) and ‘Real Fino’ apricot seedling (Prunus armeniaca L.) were analysed in an experimental orchard under organic management. The study was performed between 2010 and 2012 in the province of Seville (SW Spain). Colour, fruit and stone weights, firmness, soluble solid concentration, and acidity were measured for fruit quality evaluation. Trunk cross-sectional area, main branches, and fruit yield were also determined. In general, ‘Myrobalan 29C’ rootstock produced fruit slightly larger in size and with a bigger weight. By contrast, apricots on ‘Myrobalan 29C’ had less firmness and a lower solid soluble concentration than on ‘Real Fino’. There was little difference in the colour, acidity, and stone dry weights. Trees on ‘Real Fino’ had larger areas of trunk and branches but no significant differences were obtained in relation to fruit yields