PLUM POX VIRUS SILENCING OF C5 TRANSGENIC PLUMS IS STABLE UNDER CHALLENGE INOCULATION WITH HETEROLOGOUS VIRUSES
I. Zagrai, N. Capote, M. Ravelonandro, M. Cambra, L. Zagrai, R. Scorza
Transgenic C5 cv. Honey Sweet is a clone of Prunus domestica L. transformed with the Plum pox virus coat protein gene (PPV-CP). This transgenic plum displays post-transcriptional gene silencing (PTGS) which makes it highly resistant to PPV infection. To test the effect of heterologous viruses on the efficacy and stability of PTGS against PPV, transgenic C5 trees were graft-inoculated with different combinations of Prunus necrotic ringspot virus (PNRSV), Apple chlorotic leaf spot virus (ACLSV), Prune dwarf virus (PDV) and PPV-D strain. The potential for suppression of the silencing mechanism mediated by these viruses was evaluated. Challenge experiments were performed under greenhouse, nursery and field conditions in Romania and Spain, comprising two different environments, continental and Mediterranean, respectively. Virus infections were evaluated by visual monitoring of symptom and by serological and molecular assays. The engineered resistance to PPV in C5 transgenic plums was stable and was not suppressed by the presence of the challenging heterologous viruses over a three-year experimental period across all trials.