Evaluating molecular diagnostic techniques for seed detection of Pseudomonas savastanoi pv. phaseolicola, causal agent of halo blight disease in mungbean (Vigna radiata)

Halo blight of mungbean (Vigna radiata var. radiata) is caused by the bacterium Pseudomonas savastanoi pv. phaseolicola. This pathogen is transmitted via infected seed, facilitating the spread of the disease into new cultivated areas. Prospective mungbean seed crops are currently subjected to visual inspection as a means of determining disease status, however, this is a poor method that relies on visible symptoms and does not account for latent infections. A range of molecular diagnostics targeting P. savastanoi pv. phaseolicola have been developed, but these have not been deployed on seeds. Quantitative PCR (qPCR) SYBR assay, hydrolysis probe, and conventional PCR, using the same primers were optimised against a plate-truthed dilution series of P. savastanoi pv. phaseolicola. The detection limit of the conventional PCR assay was approximately 9,000 CFU µl-1, while both qPCR assays could detect 9 CFU µl-1. These tests were then used to screen DNA extracted from 200 g allotments of 38 seed lots comprising six mungbean cultivars representing the primary Australian production area, and two seed lots of known infection status. Of these, the pathogen was detected in six seed lots by conventional PCR. The SYBR assay and hydrolysis probe methods detected 20 and 24 infected seed lots respectively. This shows that the hydrolysis probe method was the most effective at diagnosing the presence of P. savastanoi pv. phaseolicola in mungbean seed, providing a valuable molecular diagnostic to aid in integrated disease management and seed certification, substantially mitigating losses to halo blight disease

Large-scale gene discovery in the pea aphid Acyrthosiphon pisum (Hemiptera)

Aphids are the leading pests in agricultural crops. A large-scale sequencing of 40,904 ESTs from the pea aphid Acyrthosiphon pisum was carried out to define a catalog of 12,082 unique transcripts. A strong AT bias was found, indicating a compositional shift between Drosophila melanogaster and A. pisum. An in silico profiling analysis characterized 135 transcripts specific to pea-aphid tissues (relating to bacteriocytes and parthenogenetic embryos). This project is the first to address the genetics of the Hemiptera and of a hemimetabolous insect.Beatriz Sabater-Muñoz... et al

L'évolution des virus à ARN : rôles de la sélection et de la dérive génétique

International audienceLes virus à ARN, tout comme les rétrovirus et pararétrovirus, ont la capacité d'évoluer très rapidement, grâce à des taux de mutations élevés et des temps de génération très courts. Les erreurs de réplication du génome (mutations et recombinaisons « imparfaites ») sont la source d'une grande variabilité. Cependant, des pressions de sélection sculptent les populations virales dans leur diversité en agissant à tous les niveaux du cycle infectieux des virus : stratégies d'expression du génome, interactions avec l'hôte et le vecteur sont les principales cibles de la sélection. La sélection trie en fonction de la valeur adaptative. Le second paramètre important modulant la diversité des populations virales est la dérive génétique qui intervient lorsque la taille efficace de la population est faible, ce qui semble être fréquent lors de l'initiation de l'infection d'un hôte ou d'un tissu. Contrairement à la sélection, la dérive est un facteur largement aléatoire, indépendant de la valeur adaptative et peut avoir pour conséquence la fixation de mutations délétères. Malgré des taux de mutations exceptionnellement élevés, les virus à ARN semblent également répondre aux principes classiques de la génétique des populations, comme cela a été montré au cours des deux dernières décennies

La transmission des virus de Solanacées par les pucerons

National audienceRevue de connaissance acquises au cours des 10 dernières années sur la transmission des virus des Solanacées par les pucerons. Le PVY et le PLRV, dont les modes de transmission sont sans nul doute les plus répandus et les mieux cernés, ont été choisis comme exemples

L'evolution des virus a ARN: roles de la selection et de la derive genetique

RNA viruses, retroviruses and pararetroviruses, are known for their rapid evolution, because of high mutation rates and short generation times. Replication errors (mutations and imperfect recombinations) generate a great variability. However, selection pressures shape viral populations diversity, by acting at different steps of virus infectious cycle : strategies of genome expression, interactions with host(s) and vector(s) are the targets of selection. Such a selection sorts out genotypes according to their fitness. The second most important parameter acting on viral population diversity, genetic drift, occurs when population effective size is low, which seems to be frequent during host or tissue infection initiation. By contrast to selection, drift is a random, fitness‐independent process, which may lead to the fixation of deleterious mutations. Despite their exceptionally high mutation rates, RNA viruses seem to follow classical population genetics principles, as showed during the last two decades.http://www.john-libbey-eurotext.fr/en/revues/bio_rech/vir/e-docs/00/04/04/91/resume.md?type=text.htm

Virus de l'enroulement de la pomme de terre : le point sur les recherches

National audienc

Production of recombinant Potato mop-top virus coat protein in Escherichia coli and generation of antisera recognising native virus protein

Copyright © 2003 Elsevier Science B.V. All rights reservedPotato mop-top virus (PMTV, Pomovirus) is difficult to detect because it is unevenly distributed and present at low concentration in infected tissues. The production of PMTV-free seed relies on sensitive and specific detection methods of virus detection, including serological methods. The possibility of using a PMTV recombinant coat protein (CP) as an antigen for antiserum production was investigated. The region encoding the PMTV CP was inserted into pET3A, expressed in Escherichia coli, and the recombinant PMTV CP produced was used to raise antibodies in rabbits. Three antisera were produced. All recognised efficiently the recombinant CP in Western blot analysis and the most sensitive antiserum (H5003) detected native CP on Western blots and in ELISA. Thus, recombinant CP can be used as an alternative to purified virus for the production of specific antibodies against PMTV.Valérie Hélias, Emmanuel Jacquot, Maryse Guillet, Yves Le Hingrat and Danièle Giblot-Ducrayhttp://www.elsevier.com/wps/find/journaldescription.cws_home/506080/description#descriptio

The passage of potato leafroll virus through Myzus persicae gut membrane regulates transmission efficiency.

Potato leafroll virus (PLRV) is transmitted by aphids in a persistent manner. Although virus circulation within the aphid leading to transmission has been well characterized, the mechanisms involved in virus recognition at aphid membranes are still poorly understood. One isolate in our collection (PLRV-14.2) has been shown to be non- or only poorly transmitted by some clones of aphids belonging to the Myzus persicae complex. To determine where the transmission process was blocked within the aphid, three virus transmission procedures were used. PLRV-14.2 could not be transmitted, or was only very poorly transmitted, after acquisition from infected plants or from purified preparations. In contrast, it could be transmitted with more than 70% efficiency when microinjected. Therefore, it is concluded that the gut membrane was a barrier regulating passage of PLRV particles from the gut lumen into the haemocoel of M. persicae. Comparison of coat protein (CP) and readthrough protein (RTP) sequences between poorly and readily transmissible isolates showed that PLRV-14.2 differed from other PLRV isolates by amino acid changes in both of these proteins. It is hypothesized that at least some of the changes found in CP and/or RTP reduced virus recognition by aphid gut receptors, resulting in reduced acquisition and subsequent transmission of PLRV-14.2.J. Rouzé-Jouan, L. Terradot, F. Pasquer, S. Tanguy, and D. Giblot Ducray-Bourdi

Distribution of Cardicola forsteri eggs in the gills of southern bluefin tuna (Thunnus maccoyii) (Castelnau, 1872)

The distribution of Cardicola forsteri eggs in the gills of southern bluefin tuna (Thunnus maccoyii) was analysed. Eggs were confirmed to be C. forsteri using laser-capture microdissection and quantitative polymerase chain reaction (qPCR) analyses. Prevalence of infection was significantly higher in the second gill arch (χ2 = 6.49, P < 0.05) than in the fourth gill arch, and significantly lower in the basal region of the second gill arch (χ2 = 6.29, d.f. = 2, P < 0.05). The intensity of infection was not significantly different between the gill arches (F = 0.03, d.f. = 1, P > 0.05). Similarly, there was no significant difference in the intensity of C. forsteri eggs between the gill arches (F = 3.43, d.f. = 2, P > 0.05), or at different depth of sectioning (F = 0.08, d.f. = 1.12, P > 0.05). Results suggest that the presence of C. forsteri eggs in the gills of tuna is more likely to be detected by sampling the second gill arch. Furthermore, targeting the middle region and increasing the sectioning depth may reduce the proportion of false negatives