Publications (7)14.29 Total impact
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Article: 'Candidatus Phytoplasma solani', a novel taxon associated with stolbur and bois noir related diseases of plants.
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ABSTRACT: Phytoplasmas classified in group 16SrXII infect a wide range of plants and are transmitted by polyphagous planthoppers of the family Cixiidae. Based on 16S rRNA gene sequence identity and biological properties, group 16SrXII encompasses several species, including 'Candidatus Phytoplasma australiense', 'Ca. Phytoplasma japonicum', and 'Ca. Phytoplasma fragariae'. Other group 16SrXII phytoplasma strains are associated with stolbur disease in wild and cultivated herbaceous and woody plants and with bois noir disease in grapevines (Vitis vinifera L.). Such latter strains have been informally proposed to represent a separate species, 'Candidatus Phytoplasma solani', but a formal description of this taxon has not previously been published. In the present work, stolbur disease strain STOL11 was distinguished from reference strains of previously described 'Ca. Phytoplasma' species based on 16S rRNA gene sequence (16S rDNA) similarity and a unique signature sequence in 16S rDNA. Other stolbur and bois noir associated ('Ca. Phytoplasma solani') strains shared >99% 16S rDNA sequence similarity with strain STOL11 and contained the signature sequence. 'Ca. Phytoplasma solani' is the only phytoplasma known to be transmitted by Hyalesthes obsoletus. Insect vectorship and molecular characteristics are consistent with the concept that diverse 'Ca. Phytoplasma solani' strains share common properties and represent an ecologically distinct gene pool. Phylogenetic analyses of 16S rRNA, tuf, secY, and rplV-rpsC gene sequences supported this view and yielded congruent trees on which 'Ca. Phytoplasma solani' strains formed, within the group 16SrXII clade, a monophyletic subclade that was most closely related to, but distinct from, that of 'Ca. Phytoplasma australiense'-related strains. Based on distinct molecular and biological properties, stolbur and bois noir associated strains are proposed to represent a novel species level taxon, 'Ca. Phytoplasma solani'; STOL11 is designated the reference strain.INTERNATIONAL JOURNAL OF SYSTEMATIC AND EVOLUTIONARY MICROBIOLOGY 01/2013; · 2.11 Impact Factor -
Article: Endophytic bacterial community living in roots of healthy and 'Candidatus Phytoplasma mali'-infected apple (Malus domestica, Borkh.) trees.
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ABSTRACT: 'Candidatus Phytoplasma mali', the causal agent of apple proliferation (AP) disease, is a quarantine pathogen controlled by chemical treatments against insect vectors and eradication of diseased plants. In accordance with the European Community guidelines, novel strategies should be developed for sustainable management of plant diseases by using resistance inducers (e.g. endophytes). A basic point for the success of this approach is the study of endophytic bacteria associated with plants. In the present work, endophytic bacteria living in healthy and 'Ca. Phytoplasma mali'-infected apple trees were described by cultivation-dependent and independent methods. 16S rDNA sequence analysis showed the presence of the groups Proteobacteria, Acidobacteria, Bacteroidetes, Actinobacteria, Chlamydiae, and Firmicutes. In detail, library analyses underscored 24 and 17 operational taxonomic units (OTUs) in healthy and infected roots, respectively, with a dominance of Betaproteobacteria. Moreover, differences in OTUs number and in CFU/g suggested that phytoplasmas could modify the composition of endophytic bacterial communities associated with infected plants. Intriguingly, the combination of culturing methods and cloning analysis allowed the identification of endophytic bacteria (e.g. Bacillus, Pseudomonas, and Burkholderia) that have been reported as biocontrol agents. Future research will investigate the capability of these bacteria to control 'Ca. Phytoplasma mali' in order to develop sustainable approaches for managing AP.Antonie van Leeuwenhoek 06/2012; 102(4):677-87. · 2.09 Impact Factor -
Article: Genetic diversity among ‘Candidatus Liberibacter asiaticus’ isolates based on single nucleotide polymorphisms in 16S rRNA and ribosomal protein genes
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ABSTRACT: Citrus Huanglongbing (HLB) is one of the most destructive and widespread diseases of citrus, caused by ‘Candidates Liberibacter’, a non-cultured, phloem-restricted alpha-proteobacterium. In the present study, ‘Ca. Liberibacter’ was detected in symptomatic citrus plants growing in the Karnataka state (South India) by amplification of 16S rRNA and β-operon ribosomal protein (β-rp) genes, using PCR primers specific for African and Asian ‘Ca. Liberibacter’. Sequencing of the 16S rRNA amplified fragment revealed that ‘Ca. Liberibacter’, here identified belongs to the species ‘Ca. Liberibacter asiaticus’. The alignments of 16S rRNA and ribosomal protein gene sequences of all known ‘Ca. Liberibacter asiaticus’related, allowed to recognize Single Nucleotide Polymorphisms (SNPs). Basing on SNP analysis, the strains were grouped in fourteen 16SrRNA SNP genetic lineages (16Sr-I to 16Sr-XIV) and three β-rp SNP genetic lineages (rp-I to rp-III). Only the strains of ‘Ca. Liberibacter asiaticus’ from the Karnataka state belonged to the genetic lineages 16Sr-I and rp-I. RFLP diagnostic tests on the discriminative 16S rRNA SNPs were set up to identify this lineage. These results revealed the presence of a new ‘Ca. Liberibacter asiaticus’ genetic lineage in the Indian sub-continent, where at least four genetically diverse SNP lineages were found. These findings could open new opportunities for in-depth studies on biological niches and traits of ‘Ca. Liberibacter asiaticus’. Key wordsHuanglongbing (HLB)-‘Candidates Liberibacter’-single nucleotide polymorphisms-genetic lineageAnnals of Microbiology 04/2012; 59(4):681-688. · 0.69 Impact Factor -
Article: Restructuring of endophytic bacterial communities in grapevine yellows-diseased and recovered Vitis vinifera L. plants.
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ABSTRACT: Length heterogeneity-PCR assays, combined with statistical analyses, highlighted that the endophytic bacterial community associated with healthy grapevines was characterized by a greater diversity than that present in diseased and recovered plants. The findings suggest that phytoplasmas can restructure the bacterial community by selecting endophytic strains that could elicit a plant defense response.Applied and environmental microbiology 05/2011; 77(14):5018-22. · 3.69 Impact Factor -
Article: Endophytic bacterial diversity in grapevine (Vitis vinifera L.) leaves described by 16S rRNA gene sequence analysis and length heterogeneity-PCR.
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ABSTRACT: Diversity of bacterial endophytes associated with grapevine leaf tissues was analyzed by cultivation and cultivation-independent methods. In order to identify bacterial endophytes directly from metagenome, a protocol for bacteria enrichment and DNA extraction was optimized. Sequence analysis of 16S rRNA gene libraries underscored five diverse Operational Taxonomic Units (OTUs), showing best sequence matches with gamma-Proteobacteria, family Enterobacteriaceae, with a dominance of the genus Pantoea. Bacteria isolation through cultivation revealed the presence of six OTUs, showing best sequence matches with Actinobacteria, genus Curtobacterium, and with Firmicutes genera Bacillus and Enterococcus. Length Heterogeneity-PCR (LH-PCR) electrophoretic peaks from single bacterial clones were used to setup a database representing the bacterial endophytes identified in association with grapevine tissues. Analysis of healthy and phytoplasma-infected grapevine plants showed that LH-PCR could be a useful complementary tool for examining the diversity of bacterial endophytes especially for diversity survey on a large number of samples.The Journal of Microbiology 08/2009; 47(4):393-401. · 1.10 Impact Factor -
Article: Identification and Molecular Characterization of ‘Candidatus Phytoplasma mali’ Isolates in North‐western Italy
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ABSTRACT: Apple proliferation (AP) is an important disease and is prevalent in several European countries. The causal agent of AP is ‘Candidatus Phytoplasma mali’ (‘Ca. Phytoplasma mali’). In this work, isolates of ‘Ca. Phytoplasma mali’ were detected and characterized through polymerase chain reaction (PCR) and restriction fragment length polymorphism (RFLP) analyses of 16S rRNA gene and non-ribosomal DNA fragment. The presence of three AP subtypes (AT-1, AT-2 and AP-15) was identified in 31 symptomatic apple trees and two samples each constituted by a pool of five insects, collected in north-western Italy, where AT-1 is a dominant subtype. Subsequent nucleotide sequence analysis of the PCR-amplified 1.8 kb (P1/P7) fragment, containing the 16S rDNA, the 16S–23S intergenic ribosomal region and the 5′-end of the 23S rDNA, revealed the presence of at least two phytoplasmal genetic lineages within the AT-1 subtype, designed AT-1a and AT-1b. Moreover, in silico single nucleotide polymorphism (SNP) analysis based on 16S rDNA sequence can differentiate AT-1 subtype from AT-2 and AP-15 subtypes. Our data showed a high degree of genetic diversity among ‘Ca. Phytoplasma mali’ population in north-western Italy and underlined the possible use of the 16S rDNA analysis for the identification and the geographical origin assignation of isolates of AP phytoplasma. Molecular markers on 16S rDNA, here identified, could be useful for studying the epidemiology of AP disease.Journal of Phytopathology 04/2009; 158(2):81 - 87. · 0.79 Impact Factor -
Article: A novel Bacteroidetes symbiont is localized in Scaphoideus titanus, the insect vector of Flavescence dorée in Vitis vinifera.
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ABSTRACT: Flavescence dorée (FD) is a grapevine disease that afflicts several wine production areas in Europe, from Portugal to Serbia. FD is caused by a bacterium, "Candidatus Phytoplasma vitis," which is spread throughout the vineyards by a leafhopper, Scaphoideus titanus (Cicadellidae). After collection of S. titanus specimens from FD-contaminated vineyards in three different areas in the Piedmont region of Italy, we performed a survey to characterize the bacterial microflora associated with this insect. Using length heterogeneity PCR with universal primers for bacteria we identified a major peak associated with almost all of the individuals examined (both males and females). Characterization by denaturing gradient gel electrophoresis confirmed the presence of a major band that, after sequencing, showed a 97 to 99% identity with Bacteroidetes symbionts of the "Candidatus Cardinium hertigii" group. In addition, electron microscopy of tissues of S. titanus fed for 3 months on phytoplasma-infected grapevine plants showed bacterial cells with the typical morphology of "Ca. Cardinium hertigii." This endosymbiont, tentatively designated ST1-C, was found in the cytoplasm of previtellogenic and vitellogenic ovarian cells, in the follicle cells, and in the fat body and salivary glands. In addition, cell morphologies resembling those of "Ca. Phytoplasma vitis" were detected in the midgut, and specific PCR assays indicated the presence of the phytoplasma in the gut, fat body and salivary glands. These results indicate that ST1-C and "Ca. Phytoplasma vitis" have a complex life cycle in the body of S. titanus and are colocalized in different organs and tissues.Applied and Environmental Microbiology 03/2006; 72(2):1467-75. · 3.83 Impact Factor
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Institutions
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2009–2013
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University of Milan
- Department of Plant Production
Milano, Lombardy, Italy -
Università degli Studi del Sannio
Benevento, Campania, Italy
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