| Citation | Kerr's most important work has been on crown gall of higher plants caused by Agrobacterium tumefaciens. A study of the ecology and taxonomy of the genus Agrobacterium led to a novel and successful method of biological control of crown gall by use of strain 84, a closely related non-pathogenic bacterium; the method has been widely adopted in many countries. Kerr has shown that strain 84 controlled disease by producing an antibiotic, agrocin 84, highly toxic to the pathogen; the structure of agrocin 84 as a nucleotide bacteriocin was determined by colleagues at Adelaide. He then established that pathogenicity of isolates was well correlated with their sensitivity to agrocin 84 and, for the first time for a plant pathogen, 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. Kerr went on to show that transfer of the Ti plasmid is induced by opines, the first example of substrate-induced conjugation in a bacterium. His most recent research has been on the transfer functions of pAgK84, the plasmid controlling synthesis of agrocin 84. This innovative and outstanding research set the scene for the major advances that were to be made in understanding the induction of tumours in crown gall, and in the use of the Ti plasmid in genetic manipulation. Earlier, Kerr had done important work on the biology of and infection by other soil-borne pathogens and on the epidemiology and control of blister blight, a severe disease of tea in Sri Lanka. |