PCR analysis of genomic DNA of wild-type (WT) and transgenic plants. (A) Upper panel: the expected PCR products using P1 and P2 primers indicating the occurrence of marker excision events. H2O control, no plant genomic DNA was added. CK- , non-transformed WT control plants. Lower panel: PCR products using P3 and P4 primers indicating the presence of the hygromycin resistance gene. Number indicates transgenic line number. (B) WT and resistant transgenic lines after the first virus challenge. M: DNA size marker (bp), pX9-vRNAi: pX9-hpICMV RNAi plasmid. Numbers refer to independent (17) transgenic lines.