A cRNA Probe Detects Prunus Necrotic Ringspot Virus in Three Peach Cultivars after Micrografting and in Peach Shoots following Long-term Culture at 4°C

As part of a program to develop transgenic peach (Prunus persica L. Batsch) cultivars with resistance to Prunus necrotic ringspot virus (PNRSV), we are testing a system for measuring virus in peach shoot cultures. Micrografting in vitro is used for inoculation and slot-blot hybridization, with a digoxigenin (DIG)-labeled cRNA probe complementary to the 5´ open reading frame (ORF) of PNRSV RNA 3, for detection. In this study, we investigated whether infected shoots maintain virus infection over long periods of culture at 4°C and if PNRSV-infected ‘Suncrest’ shoot cultures can serve as graft bases to transmit virus equally well into cultivars Nemaguard, Springcrest, and Suncrest. The results of RNA hybridization analysis showed that virus was present in extracts of leaf samples from 2-year-old PNRSV-infected ‘Suncrest’ shoots that had been subjected to varying lengths of incubation at 4 °C in the dark, suggesting that infected shoots can be maintained for repeated use. Rates of graft success were higher in heterografts between ‘Suncrest’ bases and tips of ‘Springcrest’ or ‘Nemaguard’ than in autografts between ‘Suncrest’ and ‘Suncrest’, and there was equal efficacy of graft inoculation from ‘Suncrest’ into these three cultivars