Instituto Valenciano de Investigaciones Agrarias, Apartado Oficial, Moncada, 46113 Valencia, Spain
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Accepted for publication 30 December 1998.
The behavior of the virulent transconjugant K84N6 derived from Agrobacterium radiobacter strain K84 after spontaneous Ti plasmid transfer in crown gall tissue in a biocontrol experiment was studied and compared with the behavior of the wild-type A. tumefaciens donor of the Ti plasmid. The main difference between the strains was a greatly reduced ability of the transconjugant to catabolize nopaline. Host range, ability to induce tumors in several fruit trees, and stability of the pathogenic determinants in isolates from tumors did not differ between the strains. Nevertheless, in a biocontrol experiment, the transconjugant was not controlled by strain K84 or K1026 in peach × almond hybrids and survived in the plant rhizo-sphere for 9 months with larger population densities than the wild strain. The appearance and persistence in soil of strains harboring a Ti plasmid in the K84 chromosomal background could represent a risk in the medium term, if they show good competitive ability.
© 1999 The American Phytopathological Society