Transformation and regeneration of English elm using wild-type Agrobacterium tumefaciens

In vitro proliferating shoots of a clone of the English elm, Ulmus procera SR4, were infected with the wild-type Agrobacterium tumefaciens strain 82.139 under a variety of conditions. A co-cultivation medium of pH 5.2 was found to be optimal for infection by uninduced A. tumefaciens 82.139, with 70-75% of inoculated shoots forming tumours. In the presence of 0.1 mM acetosyringone (a virulence inducing agent), the highest percentage tumour formation was obtained following co-cultivation at pH 5.8. The tumours were brown to white in colour, and were able to regenerate shoots capable of independent growth. Some of these shoots proved to be transformed with the T-DNA of A. tumefaciens 82.139 on the basis of nopaline production and Southern hybridisation. These results are discussed in relation to the development of a transformation protocol using disarmed agrobacteria harbouring manipulated Ti plasmids.