The Use of Transgenic Resistant Plums in Transgrafting Fails to Confer Plum Pox Virus Resistance in Prunus

Abstract

In order to sustain productivity, growers are implementing fruit trees to provide plum pox virus (PPV) resistant varieties. Unfortunately, classical breeding approaches have failed to develop resistant varieties. RNA interference (RNAi) silencing, as an alternate strategy, has been shown to be an efficient approach to combat PPV disease (sharka). PPV resistance based on RNAi has been demonstrated in natural conditions for over 10 years. Experiments using graft inoculation in high-containment greenhouses show that silencing protects against PPV over multiple dormancy cycles. While the virus spreads throughout the vascular tissues of susceptible hosts, PPV movement is undetectable in resistant clones. However, in this work, when PPV-susceptible cultivars were grafted onto transgenic resistant plum rootstocks, the small interfering RNA (siRNA) stopped the systemic spread of PPV into the transgenic resistant shoots but did not appear to prevent the infection of susceptible scions. Thus, we do not have convincing evidence of siRNA transfer nor the provision of resistance to the susceptible scion. Notably, <em>Macrolophus</em> insects that were experimentally fed on plums could suck RNAi from the leaves of resistant clones. While the attempt to control PPV disease through transgrafting as a new breeding technology (NBT) cannot be confirmed, these studies provide insight into key regulatory interactions associated with RNAi accumulation and its environmentally safe use in perennial plants.