The persistence of engineered Agrobacterium tumefaciens in agroinfected plants.

Several plant species, including tomato (Lycopersicon esculentum), Gynura aurantiaca, avocado (Persea americana), and grapefruit (Citrus paradisi) grafted on Troyer citrange (Poncirus trifoliata x C. sinensis) were "agro-infected" with Agrobacterium tumefaciens strain LBA-4404, carrying a mini-Ti plasmid with a dimeric cDNA of citrus exocortis viroid (CEVd). Extracts prepared from tissues of the agroinfected plants 38-90 days after inoculation were plated on selective media and found to contain large amounts of the engineered bacteria. These observations suggest the need for more stringent quarantine measures when handling A. tumefaciens cells harboring constructs for "agroinoculation" with plant viruses or viroids.