In situ localisation of plum pox particles in susceptible and resistant apricot cultivars

The mechanism of virus transport in woody host plants is, up to now, poorly understood. From the initially infected cells, there are two forms of spread within the plant, namely short-distance and long-distance. Short-distance spread is from one cell to an adjacent cell, whereas the long-distance spread takes place in the vascular system. The movement of viruses in plants is a complex and integrated process where different viral proteins are playing an essential role. Within the Prunus/PPV pathosystem, few data are available on the spread of the virus from the infection point to systemic long-distance organs (Dicenta et al., 2003). In this work, in situ hybridisation of a PPV CP probe was used to study the localisation of viral particles in stems of one susceptible and two partially resistant apricot cultivars, cv. 'Moniqui', 'Goldrich' and 'StarkEarlyOrange' respectively. PPV particles were detected in the close vicinity of the infection point at different stages after inoculation. By using anti-sense and sense (control) probes, the Plum pox virus is detected in different tissues from one to 30 days post inoculation. Its localisation is characterised by irregular distribution and concentration, in partially resistant cultivars, by limited virus movement from the inoculation point. In this study, it is expected that the unravelling of PPV localisation in partially resistant cultivars will allow us to describe different mechanisms of resistance to sharka disease in Prunus.