Greenhouse evaluation confirms in vitro sharka resistance of genetically engineered h-UTR/P1 plum plants

Plum pox virus (PPV), a quarantine virus, is the causal agent of sharka, the most devastating viral disease of stone fruits. The aim of this study was to produce several transgenic plum lines resistant to PPV, set up an efficient and reliable in vitro PPV resistant test and compare it with the standard greenhouse evaluation. Transgenic plants with the hairpin h-UTR/P1 construct were produced after infection of hypocotyls from mature European plum seeds with Agrobacterium tumefaciens. Ten transgenic lines were in vitro grafted onto PPV-D infected 'GF305' peach and evaluated for PPV presence by RT-PCR. PPV was detected in all non-transgenic grafts whereas in seven transgenic lines it was never found or disappeared with time. PPV-resistant transgenic lines were rooted, acclimatized and evaluated with the standard procedures under greenhouse conditions. Our data indicates that greenhouse and in vitro results agreed. The proposed in vitro evaluation method could be used to screen sharka resistant plum lines providing a fast, reliable and contained methodology.