Further Evidence that the Vitopine-type pTi's of Agrobacterium vitis Represent a Novel Group of Ti Plasmids. Erno Szegedi. Research Institute for Viticulture and Enology, H-6000 Kecskemet, P.O. Box 25, Hungary. Mihaly Czako (2), and Leon Otten (3) (2) Biological Research Center of the Hungarian Academy of Sciences, 6701 Szeged, P.O. Box 521, Hungary; (3) Institut de Biologie Moleculaire des Plantes du CNRS, 12 rue du General Zimmer, 67084 Strasbourg, France. MPMI 9:139-143. Accepted 11 October 1995, Copyright 1996 The American Phytopathological Society.

To study the incompatibility properties of the vitopine Ti plasmids of Agrobacterium vitis, pPM739 containing the cloned ori region of pTiS4 was introduced by triparental mating into seven Agrobacterium tumefaciens strains carrying incRh-1, incRh-2, and incAg-1 plasmids and into eight A. vitis strains. All strains containing pPM739 retained their original plasmids and virulence or the ability to grow on tartrate, except for the three vitopine strains S4, SzJ, and NW11. Furthermore, pTiS4 was stably maintained in S4 cells following introduction of the ori/inc clones of the incRh-1, incRh-2, and rncRh-3 plasmids. These results show that vitopine Ti plasmids represent a novel incompatibility group for which we propose the name incRh-4.