Description préliminaire d’un potyvirus isolé de courgette (Cucurbita pepo L.) en Guadeloupe

En Guadeloupe, le virus 1 de la mosaïque de la pastèque, Papaya Ringspot Virus-Watermelon (PRSV-W)= Watermelon Mosaic Virus 1 (WMV-1), est très répandu dans les cultures de courgette où il provoque des symptômes de mosaïque avec cloques et des déformations filiformes très marquées sur le feuillage et également des déformations de fruits. Depuis 1982, on a constaté qu’un autre faciès maladif était aussi épidémique dans les champs de courgette. Il se distingue de celui de PRSV-W par une mosaïque donnant un aspect tigré au feuillage et l’absence de déformation filiforme. L’isolat (Q10) provenant de l’une des plantes infectées par la souche « Tigré » a été étudié. Le virus est transmissible par inoculation mécanique. Il est transmis par puceron sur le mode non persistant mais à un taux différent de celui observé pour le PRSV-W. Sa gamme d’hôtes est analogue à celle du PRSV-W. Elle est limitée à la famille des Cucurbitacées et en particulier, les génotypes de Cucumis melo, C. metuliferus, Cucurbita ecuaderensis et C. foetidissima résistants au PRSV-W sont aussi résistants à l’isolat Q10. Les particules virales sont flexueuses. L’infection induit dans le cytoplasme la formation d’inclusions amorphes et d’inclusions cylindriques se classant dans la subdivision I. Des tests sérologiques d’immunodiffusion en présence de dodécyl-sulfate de sodium et des tests en ISEM (Immunosorbent Electron Microscopy) ont montré que l’isolat Q10 ne réagissait avec aucun des sérums dont nous disposions préparés contre les virus suivants : PRSV-W, Watermelon Mosaic Virus 2 (WMV-2), Watermelon Mosaic Virus « Morocco » (WMV-M), Zucchini Yellow Mosaic Virus (ZYMV), Zucchini Yellow Fleck Virus (ZYFV). Inversement, PRSV-W, WMV2 et ZYMV n’ont pas réagi avec le sérum préparé spécifiquement contre l’isolat Q10. L’isolat Q10 a des propriétés biologiques proches de celles du PRSV-W ; il s’en distingue par son taux de transmission par puceron, sa symptomatologie sur certains hôtes et par ses propriétés sérologiques. Une étude complémentaire permettra d’établir si cet isolat doit être considéré comme un sérotype du PRSV-W ou comme un virus à part entière.In Guadeloupe, a Caribbean island, the watermelon strain of papaya ringspot virus (PRSV-W = watermelon mosaic virus 1, WMV-1) is commonly encountered in squash fields. It induces a severe mosaic with blistering and filiformism on squash leaves, and a deformation of fruits. Since 1982, a new disease has been found epidemically in squash fields, the symptoms being leaf discoloration according to a striped ("Tigre") pattern and limited filiformism. An isolate (Q10), collected from a squash showing the "Tigre" symptom, was studied. The virus was transmitted mechanically and also transmitted by aphids in the non-persistent manner and less efficiently than PRSV-W. Its host range was similar to that of PRSV-W. It was restricted to the Cucurbit family, and genotypes of Cucumis melo, C. metuliferus, Cucurbita ecuadorensis and C. foetidissima resistant to PRSV-W were also resistant to isolate Q10. Virus particles were filamentous. Infection induced in the cytoplasm the formation of amorphous and cylindrical type I inclusions. Sodium dodecyl sulfateimmunodiffusion and ISEM (Immunosorbent Electron Microscopy) tests showed that isolate Q10 did not react with sera prepared against the following viruses : PRSV, watermelon mosaic virus 2 (WMV-2) watermelon mosaic virus "Morocco" (WMV-M), zucchini yellow mosaic virus (ZYMV), zucchini yellow fleck virus (ZYFV). Conversely, PRSV-W, WMV-2 ans ZYMV did not react with the serum specifically prepared against isolate Q10. Some biological properties of isolate Q10 and PRSV-W were similar but the viruses could be distinguished by their aphid transmission rate, symptoms on some hosts and serological properties. Further studies will show whether this isolate should be considered as a new serotype of PRSV or as a new virus

The behaviour of alate aphids inside a Prunus orchard : an element to take into account in Plum Pox Virus spread ?

National audienceAphid-borne viruses are depending on flight behaviour of their vectors for spreading. When spread takes place in orchards as it is the case for plum pox virus, the flight behaviour of aphids can be modified by the effect of the orchard on the wind. The aim of this experiment was to document both the effect of the orchard on wind speed and its consequence on aphid flight behaviour. Data on the wind speeds inside an apricot orchard demonstrated that the wind speed at the foliage level and at the bottom of the trees is decreased under the value of 1 m/s (speed limit for actively oriented aphid flight). As a consequence, aphids have the possibility to make actively oriented flights inside the orchard most of the time. This was confirmed by a capture-recapture experiment with marked aphids. It can be deduced from the results that the geometry of orchards should be taken into account for analysing spatial pattern of virus spread

Influence de la vitesse et de la direction du vent sur la capture des pucerons ailés par un piège à fils englués

International audienc

Transmission des potyvirus par les pucerons, facteur Helper

National audienc

Aphids can acquire plum pox virus from infected fruits

UMR BGPI Equipe 6International audienceStone fruit trees can produce fruits even after Plum pox virus (PPV) infection. These fruits can be left in the orchard if unmarketable or marketed if symptomless, elsewhere and possibly thrown away at this new place. Hence, if infected fruits can be a virus source for aphids, they provide a way of dissemination of PPV. To test the hypothesis that PPV could be acquired from infected fruits, we used apricots and peaches produced from trees infected by PPV strains D and M and maintained under an insect proof screenhouse. Four stages of maturity were assessed, from the beginning of fruit formation to a post-maturity stage. Transmissions were carried out by Myzus persicae. Test plants were seedlings of Prunus persicae cv GF 305. We demonstrate that aphids can transmit PPV from infected apricots or peaches to peach seedlings, even from symptomless fruits. Both PPV strains were transmitted. Transmissions were obtained at all the stages of fruit ripening, even with rotting fruits. To demonstrate that aphids can land on fruits, healthy fruits were glued and exposed in trays under field conditions. Aphids belonging to several species (including known PPV vectors) were caught. Infected fruits can thus be a virus source for aphids and can provide a pathway for PPV dissemination

Variabilite chez le virus des taches en anneau du Papayer

National audienc

Plum Pox Virus susceptibility of several Prunus rootstocks used for Apricot

National audiencePlum Pox Virus (PPV) is a serious threat for stone fruit production as there is no resistant variety commercially available. However, breeding for apricot resistance to PPV is in progress. This justifies an evaluation of the susceptibility of common rootstocks in order to boost the release of efficient methods of PPV control. The susceptibility of eight rootstocks is tested against five PPV isolates corresponding to the variability of the virus in France. A first experiment performed under greenhouse with plantlets growing in pots showed differences in susceptibility. A second five-year experiment was performed on rootstocks grown in deep soil, under insect-proof conditions to avoid cross contamination by aphids. Monitoring of infection was carried out by symptomatologic observations and DAS-ELISA tests. Analysis of data allows to notice differences along four parameters: symptomatology, latency (which can extend from 0.2 to more than 4 years), virus titer measured by ELISA OD, and stability of infection evaluated by the repeatitivity of ELISA detections throughout the years. The rootstocks susceptibility shows a differencial interaction according to the PPV isolates. Globally it appears that three rootstocks are susceptible to the five PPV isolates, four rootstocks are not infected by some or by all the PPV-D types, and one rootstock (GF677) shows resistance or only faint and transient virus multiplication. However, until now, limited experiments show that GF677 appears inefficient to protect a susceptible grafted variety against PPV infection

Détection et identification sérologiques des infections naturelles par le virus de la mosaïque du concombre

National audienc