1,721,013 research outputs found
Molecular tools in COST FA0807 Action
Full text linkFollowing the application of molecular technologies the phytoplasma phylogeny was resolved and led to the new trivial name of phytoplasma and to the designation of a new taxon named ‘Candidatus phytoplasma’. Because of the highly conserved nature of the 16S rDNA, many biologically or ecologically distinct phytoplasma strains, which warrant designation of a new taxon may fail to meet the requirements necessary for their differentiations. Some additional tools for phylogenetic analyses and finer strain differentiation such as rp, secY, tuf, groEL genes, and the 16S-23S rRNA spacer region sequences were used as supplementary tools or developed to provide useful and reliable taxonomic information in combination with 16S rDNA
Dissecting the multifaceted mechanisms that drive leafhopper host-phytoplasma specificity.
No full textPlant pathogen-vector complexes cause some of the most important diseases of crops worldwide, and are among the most difficult to manage effectively. Novel strategies are now needed for their management based on mechanistic understanding of transmission processes. Since the publication by Academic Press of a four-volume series on Vector Biology by Maramorosch et al during the 1970-80’s’s there have been no follow-on reference books that offer a contemporary treatment of pathogen-vector interactions and vector biology. The chapters in the proposed book will be written by well-known vector biologists from the fields of entomology and plant virology and pathology, in the instances for which it was possible, the authors together represent both perspectives. Several chapters are authored by experts outside the arena of vector interactions, but bring valuable, cross-disciplinary perspectives to relevant aspects of many vector-transmission systems, in particular the chapter on saliva and chemical ecology of plant vector-host interactions. The inclusion of chapterlets on ‘emerging pathogen-complexes is suggested in order to raise awareness of these newly occurring diseases that remain poorly studied and whose inclusion in the book will highlight the need for attention by the community. In any case, each author brings expertise and breadth in pathogen-vector interactions in distinct focus areas. For certain systems the level of knowledge is in its infancy (emergent), while for others specific molecular and cellular components are well known to govern the transmission processes, while others are in intermediate stages of elucidation. A Glossary of Terms is planned and Elaine Backus (entomology, feeding behavior) has agreed to take the lead on this section and J.K. Brown will work with her to bring the virology perspective
Molecular variability and host distribution of ‘candidatus phytoplasma solani’ strains from different geographic origins
Full text linkThe knowledge of phytoplasma genetic variability is a tool to study their epidemiology and to implement an effective monitoring and management of their associated diseases. ‘Candidatus Phytoplasma solani’ is associated with “bois noir” disease in grapevines, and yellowing and decline symptoms in many plant species, causing serious damages during the epidemic outbreaks. The epidemiology of the diseases associated with this phytoplasma is complex and related to numerous factors, such as interactions of the host plant and insect vectors and spreading through infected plant propagation material. The genetic variability of ‘Ca. P. solani’ strains in different host species and in different geographic areas during the last two decades was studied by RFLP analyses coupled with sequencing on vmp1, stamp, and tuf genes. A total of 119 strains were examined, 25 molecular variants were identified, and the variability of the studied genes was linked to both geographic distribution and year of infection. The crucial question in ‘Ca. P. solani’ epidemiology is to trace back the epidemic cycle of the infections. This study presents some relevant features about differential strain distribution useful for disease monitoring and forecasting, illustrating and comparing the phytoplasma molecular variants identified in various regions, host species, and time periods
Molecular polymorphism in phytoplasmas infecting peach trees in Serbia
No full textDuring survey carried out in 2008 to verify phytoplasma presence in fruit trees in Serbia, samples were collected from two single peach plants (30-Niš and 103-Radmilovac) showing yellows disease and phytoplasma detection was carried out using PCR assays with primer pair P1/P7 in direct reaction, followed by nested PCR with F1/B6, R16F2n/R2, and R16(I)F1/R1. RFLP analyses carried out on R16F2n/R2 amplicons with Tru1I, TaqI, Tsp509I, AluI, and BfaI restriction enzymes showed that in peach 30, a mixed phytoplasma infection was present. Tentatively identification of 16SrII and 16SrXII phytoplasmas was confirmed by RFLP analyses carried out on amplicons obtained with primers R16(I)F1/R1 with Tru1I and Tsp509I restriction enzymes. RFLP analyses on F1/B6 and R16F2n/R2 amplicons with Tru1I showed that 16SrII group phytoplasmas were present also in peach 103.
F1/B6 and R16F2n/R2 amplified products (about 1700 bp and 1200 bp respectively) of both peach samples were purified using Qiagen PCR Purification Kit (Qiagen GmbH, cloned in DH5 alfa and a number of clones was screened by PCR with M13 primers followed in nested PCR by F1/B6 and R6F2n/R2 primers (according with amplicons). RFLP analyses with Tru1I on R16F2n/R2 amplicons of seven M13 clones obtained from peach 30 show the presence of 6 profiles referable to 16SrXII and two referable to 16SrII phytoplasmas. AluI restriction enzyme did not show polymorphisms and distinguished between groups 16SrII and 16SrXII while Tsp509I showed different profiles between the two 16SrII group phytoplasmas. Similar results were obtained with Tru1I and AluI restriction enzymes on 3 clones amplified with R16(I)F1/R1. Peach 103 clones were all identical after RFLP analyses. This is the first report of 16SrII phytoplasmas in peach and the 16Sr DNA variability detected in both 16SrXII and 16SrII phytoplasmas is an indication of phytoplasma population presence in the infected plant
First insights into the genome of ‘Candidatus Phytoplasma rubi’ highlight effector protein repertoire of 16SrV phytoplasmas
No full textThe elm yellows phytoplasma group include phytopathogenic strains associated with important insect vector-borne diseases in grapevine, alder, elm, Chinese jujube and Rubus spp. such as raspberry and blackberry. The Rubus stunt disease is associated with the presence of ‘Candidatus Phytoplasma rubi’. In contrast to other 16SrV phytoplasma taxa “flavescence dorée” and ‘Ca. P. ziziphi’, no genome sequence of this phytoplasma is available. The complete genome of ‘Ca. P. rubi’ strain RS enabled a comprehensive analysis of the derived protein content. First analyses revealed a group-specific 16SrV metabolism as well as a diversified secretome that includes two conserved effector proteins
Differentiation of ‘Candidatus Phytoplasma cynodontis’ based on 16S rRNA and groEL genes and identification of a new subgroup, 16SrXIV-C.
No full text‘Candidatus Phytoplasma cynodontis’ is widespread in bermudagrass and has only been found in monocotyledonous plants. Molecular studies carried out on strains collected in Italy, Serbia, and Albania enabled verification of molecular variability in the 16S ribosomal RNA (rRNA) gene. Based on restriction fragment length polymorphism and sequence analyses, the strains from Serbia were clearly differentiated from all others and assigned to a new ribosomal DNA (rDNA) subgroup designated as 16SrXIV-C. A system for amplification of fragments containing the ‘Ca. P. cynodontis’ groEL gene was developed to enable study of its variability in related strains belonging to different 16SrXIV subgroups. Despite the fact that the groEL gene exhibited a greater sequence variation than 16S rRNA, the phylogenetic tree based on groEL gene sequence analysis was highly congruent with the 16S rDNA-based tree. The groEL gene analyses supported differentiation of the Serbian strains and definition of the new subgroup 16SrXIV-C. Phylogenetic analyses of both genes confirmed distinct phylogenetic lineages for strains belonging to 16SrXIV subgroups. Furthermore, groEL is the only nonribosomal marker developed for characterization of ‘Ca. P. cynodontis’ thus far, and its application in molecular surveys should provide better insight into the relationships among these phytoplasmas and correlation between strain differentiation and their geographical distribution
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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