Figure 3. Northern blot detection of transgene-derived small interfering RNAs in transgenic plum rootstocks and grafted wild-type apricots. siRNAs were hybridized with a DIG-labeled RNA probe corresponding to the plum pox virus h-UTR/P1 cassette (Di Nicola et al., 2005). Primers are a 20 or 25-nucleotides-length DNA oligo.