Allen Kerr’s most important work has been on crown gall of plants caused by Agrobacterium tumefaciens. A study of the ecology and taxonomy of the genus Agrobacterium led to a novel method of biological control of crown gall by use of strain 84. Allen has shown that strain 84 controls disease by producing an antibiotic, agrocin 84, highly toxic to the pathogen.
He then established that pathogenicity of isolates was well correlated with their sensitivity to agrocin 84 and that pathogenicity could be transferred from virulent to avirulent bacteria. This discovery was crucially important in supporting work by others which was establishing that pathogenicity is encoded by the Ti plasmid of A. tumefaciens.
Allen subsequently researched the transfer functions of pAgK84, the plasmid controlling agrocin 84 synthesis. He constructed a deletion mutant of K84, which in 1988 became the first genetically engineered organism to be released for commercial use in 1988. This set the scene for understanding the induction of tumours in crown gall, and in the use of the Ti plasmid in genetic manipulation.
Foreign Associate (retired), National Academy of Sciences (NAS)