Molecular Systematics of Biotype III Ti Plasmids of Agrobacterium tumefaciens. F. Paulus. Institut de Biologie Moléculaire des Plantes du CNRS, Rue du Général Zimmer 12, 67000 Strasbourg, France. B. Huss(1), G. Bonnard(1), M. Ride(2), E. Szegedi(3), J. Tempe(4), A. Petit(4), and L. Otten(1). (1)Institut de Biologie Moléculaire des Plantes du CNRS, Rue du Général Zimmer 12, 67000 Strasbourg, France; (2)INRA, Route St. Clément, 49070 Beaucouzé, Angers, France; (3)Research Institute of Viticulture and Oenology, P.O. Box 25, 6000 Kecskemet, Hungary, and (4)Institut de Microbiologie, Bâtiment 409, Université de Paris-Sud, 91405 Orsay, France.. MPMI 2:64-74. Accepted 3 January 1989. Copyright 1989 The American Phytopathological Society.

Fifty-four oncogenic grapevine isolates of Agrobacterium tumefaciens belonging to biotype III and two from biotype I were tested for host range, tumor morphology on Kalanchoë tubiflora, opine utilization, and opine production in the tumors. They were subsequently compared at the DNA level by using one T-region probe from a biotype I and two different T-region probes from a biotype III strain. The biotype III probes were selected after cloning and mapping the T-regions of two different types of octopine-cucumopine biotype III strains, Tm4 and AB3. Homology mapping with subfragments of the TL region of the octopine biotype I Ti plasmid Ach5 allowed the localization of a number of putative oncogenes on the Tm4 and AB3 T-regions. By using Ach5, Tm4, and AB3 T-region probes, the various isolates could be classified into four main groups: nopaline strains, octopine-cucumopine strains with a large TA region, octopine-cucumopine strains with a small, partially deleted TA region, and vitopine strains. Octopine-cucumopine Ti plasmids contain characteristic repeats that are closely linked to the T-regions and can also be found, in varying copy numbers, on the chromosome. All vitopine strains contain the same type of repeats, which are plasmid located. A few strains had unique homology patterns and might have special oncogenic properties. The correlations between T-region structure, opine type, and tumor-induction properties are discussed.