Résumé
Maize streak virus (MSV), family Geminiviridae, genus Mastrevirus, is transmitted in a persistent, circulative manner by several leafhoppers, mainly Cicadulina mbila. Although no evidence is available to support MSV multiplication in its vector, MSV is usually retained through the life of the leafhopper vector. Furthermore, MSV concentration usually increases during sustained feeding of leafhoppers on MSV infected maize, unlike Tomato yellow leaf curl virus for which the accumulation was shown to be limited in its whitefly vector. These observations suggest that MSV is efficiently accumulated in the insect body for an extended period during the vector's lifespan. Spatial distribution of MSV within C. mbila monitored with quantitative polymerase chain reaction (Lett et al., 2002, Phytopathology 92:65-74), showed that MSV is mainly stored in the intestinal tract. Using thin-sectioning electron microscopy (TEM) of leafhoppers that acquired MSV for 14 or 30 days from diseased maize plants, crystalline arrays of MSV-like particles were found in the cytoplasm of epithelial cells of the filter chamber in its vector C. mbila. These viruslike arrays were identified as MSV particles since they reacted with MSV antibodies by immunogold labeling of thin sections. These cytoplasmic MSV accumulations in the leafhopper were somewhat similar to those detected in the nuclei of infected plants also by gold-labeling TEM. In osmium-fixed samples, some MSV accumulations in the midgut epithelium seemed to be bound by membranes. These crystalline arrays were not detected in control leafhoppers that were not exposed to infected plants. The significance of these observations in understanding the mode of MSV transmission by leafhoppers will be discussed. (Texte intégral)