VIEW ARTICLE

Disease Control and Pest Management

Biological Control of Crown Gall with an Agrocin Mutant of Agrobacterium radiobacter. D. A. Cooksey, Graduate research assistant, Department of Botany and Plant Pathology, Oregon State University, Corvallis 97331, Present address of senior author: Department of Plant Pathology, University of California, Riverside 92521; L. W. Moore, associate professor, Department of Botany and Plant Pathology, Oregon State University, Corvallis 97331. Phytopathology 72:919-921. Accepted for publication 18 December 1981. Copyright 1982 The American Phytopathological Society. DOI: 10.1094/Phyto-72-919.

A mutant of Agrobacterium radiobacter K84 that no longer produced agrocin 84 was obtained by mitomycin C curing of the 30 Mdalton bacteriocinogenic plasmid in K84. This mutant (designated K84Agr^–) no longer prevented crown gall of tomato stems when coinoculated with an agrocin-sensitive pathogen A. tumefaciens K24. However, it effectively reduced infection when it was placed on the host plant 24 hr before the pathogen. In addition, either K84 or K84Agr^– reduced infection by agrocin-resistant A. tumefaciens B6 when the antagonists were applied 24 hr before the pathogen. Tumor weights were reduced when K84Agr^– was coinoculated with K24 or B6, or when it was applied 24 hr before the pathogens. The data suggest that other mechanisms, such as physical blockage of infection sites, are involved in biological control by K84 in addition to production of agrocin 84.