Petria 22 (3), 123-461 (2012) -22nd ICVF 381 ROBUST AN D WIDE SPECTRUM RNA SILEN CING MEDIATED RESISTAN CE TO PLUM POX VIRUS E. Di Nicola-Negri1, M. Tavazza2, V. Ilardi1 1Consiglio per la Ricerca e la Sperimentazione in Agricoltura, Centro di Ricerca per la Patologia Vegetale, Rome, Italy; 2ENEA CR Casaccia, Via Anguillarese, 301, 00123 Rome, Italy E-mail: vincenza.ilardi@entecra.it Plum pox virus (PPV) is a quarantine virus that causes sharka, one of the most important diseases of stone fruits worldwide. Seven PPV strains have been characterized, of which PPV-D, -M and Rec are the most important from an agroeconomical point of view. The best agricultural sustainable approach to prevent sharka disease consists in developing PPV-resistant plants. In this context we have shown that Nicotiana benthamiana plants transformed with PPV-M sequences (PPVIsPaVe44), covering the 5’UTR region, P1 and HC-Pro genes and arranged to express self-complementary ‘hairpin’ RNAs, are immune to the homologous PPV-ISPaVe44. However, as the RNA silencing-mediated resistance operates in a sequence-specific fashion, transgenic plants harboring the four hairpin constructs were also challenged with viral isolates belonging to different PPV strains. All the transgenic plant lines were resistant to PPV-D, –M and Recc strains. Moreover, the transgenic plant line harboring the 5’ UTR/P1 sequence was also resistant to isolates of PPV-EA and PPV-C strains that are distantly related to ISPaVe44. Since it’s known that some abiotic - low temperature - and biotic stresses - mixed viral infection - could have a detrimental impact on RNA silencing-mediated viral resistances, 5’ UTR/P1 plants were challenged with PPV under different conditions. Transgenic plants were resistant to PPV infection both at high (30°C) and low temperature (15°C). Furthermore, no susceptibility to PPV-Was observed in 5’UTR/P1 plants previously inoculated with Potato virus Y (PVY), Cucumber mosaic virus (CMV) or Artichoke mottled crinkle virus (AMCV) suggesting that prior virus-mediated expression of HCPro (PVY), 2b (CMV) and P19 (AMCV) RNA silencing suppressors was not able to defeat PPV resistance. The overall data suggest that the 5’ UTR/P1 hairpin construct can be profitably used to confer resistance to the sharka disease in Prunus species.