HOST RANGE ENCODED BY THE AGROBACTERIUM-TUMEFACIENS TUMOR-INDUCING PLASMID PTIAG63 CAN BE EXPANDED BY MODIFICATION OF ITS T-DNA ONCOGENE COMPLEMENT

A. tumefaciens harboring a pTiA6 incite unorganized tumors on Nicotiana rustica, sunflowers, carrots and tomatoes; isogenic strains of agrobacteria harboring pTiAg63 form rooty tumors on N. rustica and are essentially avirulent on sunflowers, carrots and tomatoes. The different host range characteristics of these 2 plasmids were due, in part, to differences in the T-DNA oncogene complements of the plasmids. Specifically, derivatives of pTiAg63 that contained pTiA6 oncogenes 4, 6a and 6b inserted into the TB-DNA region were constructed and agrobacteria harboring these plasmids could incite unorganized tumors on N. rustica, tomatoes, carrots and the inbred sunflower line HA202R. Undefined host factors also appeared to be involved in determining A. tumefaciens host range since 3 inbred sunflower lines, HA303B, HA89B and HA290B, were susceptible to tumor formation by agrobacteria harboring pTiA6 but not by strains harboring pTiAg63 or the modified pTiAg63 plasmids.