cqvip:Stone fruits are an important crop in most parts of the world and are heavily challenged by several viruses including Plum pox virus (PPV), Prune dwarf virus (PDV), Prunus necrotic ringspot virus (PNRSV), and Apple chlorotic leaf spot virus (ACLSV). We validated the PPV resistance in C5 plum plants (commercially known as HoneySweet) grown in the Czech Republic for more than 16 years in a field trial experiment under natural environmental conditions. We quantified single (PPV-Rec) and mixed viruses (PPV-Rec+ACLSV, PPV-Rec+PDV and PPV-Rec+ACLSV+PDV) in C5 transgenic plums inoculated for the period 2016 to 2018. The accumulation of PPV-Rec was high (~5.43E+05 copies) compared with that of ACLSV (~8.70E+04 copies) in the inoculated graft of C5 transgenic plants. Leaves close to the inoculum sources showed a differential level of virus titre in single and mixed infections (~10 to ~5×10^2 copies). C5 plants with permanent virus pressure showed 103- to 105-fold fewer copies of viruses than those of the inoculated graft. We observed high accumulation of conserved miRNAs such as miR167, miR69 and miR396 in C5 plants co-infected with PPV, ACLSV and PDV that are associated with its resistance against viruses. Overall, i) C5 transgenic plums showed high resistance to PPV infection, and a low level (~32 copies) of PPV only accumulated in some grafted plants, ii) high accumulation of PPV was found in inoculated grafts in single PPV infection and mixed infections, iii) heterologous virus infection sustained by ACLSV or PDV did not suppress PPV resistance, and iv) high and low conserved microRNAs accumulated in C5 plants.
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