Submitted to: University of Agricultural Sciences and Veterinary Medicine Cluj-Napoca
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/6/2008
Publication Date: 4/4/2008
Citation: Zagrai, I., Ravelonandro, M., Scorza, R., Minoiu, N., Zagrai, L. 2008. Bulletin of University of Agricultural Sciences and Veterinary Medicine Cluj-Napoca. University of Agricultural Sciences and Veterinary Medicine Cluj-Napoca. 65(1-2):358:365. Interpretive Summary: Genetic engineering offers the promise of disease control through non-chemical means. This technology could have important uses for tree fruits which are subject to a number of difficult to control disease problems including virus diseases. One of the most devastating virus diseases affecting stone fruit trees (plums, apricots, peaches, and cherries) is Plum pox virus (PPV) which is an exotic disease organism that has recently invaded the U.S. We have developed PPV resistant plum trees through genetic engineering. To test for the level of resistance to PPV and for the durability of resistance, and to test for resistance to PPV even in the presence of other stone fruit viruses, long-term field tests were developed in Romania, a country that has a very serious high level of PPV infection in its plum orchards. After nine years of field testing our resistant plum tree named 'HoneySweet', we found that no 'HoneySweet' trees could be naturally infected with PPV (by the aphid insect vector), even though, most of the surrounding non-genetically engineered trees became infected. We also showed that even in the presence of other plum virus diseases, 'Honeyweet' remained resistant to PPV. These tests showed conclusively that the genetically engineered plum variety, 'HoneySweet' is highly resistant to PPV and that the resistance has been durable for nearly a decade so far. This work shows the great potential of genetic engineering for disease control in fruit trees.
Technical Abstract: 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 Sharka resistance under high infection pressure in field trials in Romania. Transgenic clone C5, subsequently named "HoneySweet", showed high resistance to PPV. None of C5 trees became naturally infected by aphids during the experimental period (between five and ten years). The resistance of C5 is based on post-transcriptional gene silencing (PTGS). Therefore, we also assessed the effect of heterologous viruses on the efficacy and stability of PTGS against PPV. C5 trees were graft-inoculated with different combinations of Prunus necrotic ringspot virus (PNRSV), Prune dwarf virus (PDV), and PPV-D strain. The potential for suppression of the silencing mechanism mediated by these viruses was evaluated in the orchard and nursery. Across both trials, the engineered resistance to PPV in C5 transgenic plums was stable and was not suppressed by the presence of the assayed heterologous viruses over a three-year experimental period.