Identification and typing of grapevine phytoplasma amplified by graft transmission to periwinkle

Yellows of grapevine are spreading in many parts of the world and have been attributed to mycoplasma-libe organisms (MLOs; phytoplasma). A classification and basic understanding of grapevine phytoplasma requires samples of sufficient size which are not easy to prepare. Various phytoplasma isolates have been graft-transmitted from grapevine to periwinkle. Using PCR we show that the various phytoplasma types found in grafted periwinkle faithfully match the type found in the donor grapevine. PCR analysis of phytoplasma in periwinkle was more pronounced than the respective analysis in the donor grapevine. Therefore transmission to periwinkle may facilitate the study of grapevine phytoplasma

Potential leafhopper vectors of phytoplasma in carrots.- International Journal of Tropical Insect Science, 24: 228-235. Authors’ addresses: Bojan DUDUK (corresponding author, [email protected]

Abstract. Phytoplasmas are insect-vectored pathogens that cause characteristic and destructive diseases in carrots and other vegetables. A phytoplasma disease was first observed in Israeli carrot fields in 1995. Analysis of infected carrots showed the presence of aster yellows and western-X phytoplasmas. In this study, commercial and experimental fields in the western Negev region of Israel were monitored for three years using yellow sticky traps and vacuum sampling. Potential vectors of leafhoppers and planthoppers were analysed by PCR for the presence of phytoplasma DNA. Infected plants were also assayed for phytoplasma DNA. Extracted phytoplasma DNA was subjected to RFLP analysis to determine groups to which the phytoplasmas belonged. It was determined that carrots and leafhoppers from the experimental station were infected with a phytoplasma belonging to the Elm Yellows (EY) group; this is the first report of EY infecting carrots. Based on our findings, the two most probable insect vectors are Circulifer haematoceps complex (Mulsant & Rey) and Neoaliturus fenestratus (Herrich-Schäffer). Key words: carrot, phytoplasma, vectors, Circulifer haematoceps, Neoaliturus fenestratus Résumé. Les phytoplasmas sont des pathogènes transmis par des insectes vecteurs, responsables de maladies destructives et caractéristiques sur les carottes et d'autres légumes. Une maladie à phytoplasma a été observée pour la première fois en Israël en 1995 dans des champs de carottes. L'analyse des carottes infectées à révélé la présence des phytoplasmas aster jaunes et western-X. Dans cette étude, des parcelles expérimentales et commerciales situées dans la région Ouest du Negev en Israël ont été suivis pendant 3 ans en utilisant des pièges englués jaunes et des pièges à succion. Les vecteurs potentiels, des cicadelles et les jassides, ont été analysés par PCR afin de contrô ler la présence du DNA de phytoplasma. Les plantes infectées ont également été contrô lées pour le DNA de phytoplasma. Le DNA extrait a été soumis à une analyse par RFLP afin de déterminer le groupe d'appartenance des phytoplasmas. On a ainsi pu déterminer que les carottes et les jassides de la station expérimentale étaient infectés par des phytoplasmas du groupe Elm Yellows (EY); Il s'agit du premier signalement de carottes infectées par des phytoplasmas du groupe EY. Sur la base de nos résultats, le complexe Circulifer haematoceps (Mulsant et Rey) et Neoaliturus fenestratus (Herrich-Schäffer) sont probablement les deux principaux vecteurs

Variable Lipoprotein Genes of Mycoplasma agalactiae Are Activated In Vivo by Promoter Addition via Site-Specific DNA Inversions

Mycoplasma agalactiae, the etiological agent of contagious agalactia of small ruminants, has a family of related genes (avg genes) which encode surface lipoprotein antigens that undergo phase variation. A series of 13 M. agalactiae clonal isolates, obtained from one chronically infected animal over a period of 7 months, were found to undergo major rearrangement events within the avg genomic locus. We show that these rearrangements regulate the phase-variable expression of individual avg genes. Northern blot analysis and reverse transcription-PCR showed that only one avg gene is transcribed, while the other avg genes are transcriptionally silent. Sequence analysis and primer extension experiments with two M. agalactiae clonal isolates showed that a specific 182-bp avg 5′ upstream region (avg-B(2)) that is present as a single chromosomal copy serves as an active promoter and exhibits a high level of homology with the vsp promoter of the bovine pathogen Mycoplasma bovis. PCR analysis showed that each avg gene is associated with the avg-B(2) promoter in a subpopulation of cells that is present in each subclone. Multiple sequence-specific sites for DNA recombination (vis-like), which are presumably recognized by site-specific recombinase, were identified within the conserved avg 5′ upstream regions of all avg genes and were found to be identical to the recombination sites of the M. bovis vsp locus. In addition, a gene encoding a member of the integrase family of tyrosine site-specific recombinases was identified adjacent to the variable avg locus. The molecular genetic basis for avg phase-variable expression appears to be mediated by site-specific DNA inversions occurring in vivo that allow activation of a silent avg gene by promoter addition. A model for the control of avg genes is proposed