Agrobacterium-mediated transfer of cloned DNA copies of infectious viral genomes to plant tissues has been termed “agroinoculation” or “agroinfection” (for review, see ref. 1). The technique has been used successfully for a wide variety of virus groups, including the caulimoviruses and badnaviruses (genomes of double-stranded [ds] DNA) (2–4) the geminiviruses (ssDNA genomes) (5–7), the phloem-restricted luteoviruses (ssRNA genomes) (8), as well as for viroids (ssRNA) (9). For viruses with RNA genomes and viroids, cloned cDNA copies of the viral genome are required. Agroinfection of viruses (or viroids) with circular genomes requires the insertion of tandem multimeric copies of the genome between the T-DNA borders of an Agrobacterium binary vector, but for RNA viruses with linear genomes a cDNA copy of the genome must be inserted between a promoter (usually, the cauliflower mosaic virus 35S promoter [CaMV 35S]) and a transcription termination signal (e.g., the nopaline synthase terminator) (8).