FIELD RELEASE OF TRANSGENIC PLUMS IN ROMANIA

Transgenic clones C2, C3, C4, C5, C6, PT3 and PT5 of Prunus domestica L. transformed with the Plum pox virus coat protein gene (PPV-CP) were evaluated for Shar ka resistance under high infection pressure in field natural conditions in Romania. Tr ansgenic clone C5, recently named "HoneySweet", showed high resistance to PPV. None of the C5 trees became s naturally infected by aphids for more than ten ye ars. Known to develop the post-transcriptional gene sile ncing (PTGS) mechanism, we assessed the effect of heterologous viruses on the efficacy and stability of PTGS displayed by the C5 plum against PPV. In this way, C5 trees were graft-inoculated with different combi nations of Prunus necrotic ringspot virus (PNRSV), Prune dwarf virus (PDV) and PPV-D strain. The potential for suppress ion of the silencing mechanism mediated by these ilarviruses was evaluated in orchard and nurs ery. Both trials showed that, the engineered resist ance to PPV in C5 transgenic plums was stable and was not suppr essed by the presence of the assayed heterologous v iruses over a three-year experimental period.