MANAGEMENT OF FIRE BLIGHT - A CASE-STUDY IN MICROBIAL ECOLOGY

Suppression of the blossom-blight phase of fire blight is a key point in the management of this destructive and increasingly important disea se of apple and pear. For blossom infection to occur, the causal bacte rium, Erwinia amylovora, needs to increase its population size through an epiphytic phase that occurs on stigmatic surfaces. Knowledge of th e ecology of the pathogen on stigmas has been key to the development o f predictive models for infection and optimal timing of antibiotic spr ays. Other bacterial epiphytes also colonize stigmas where they can in teract with and suppress epiphytic growth of the pathogen. A commercia lly available bacterial antagonist of E. amylovora (BlightBan, Pseudom onas fluorescens A506) can be included in antibiotic spray programs. I ntegration of bacterial antagonists with chemical methods suppresses p opulations of the pathogen and concomitantly, fills the ecological nic he provided by the stigma with a nonpathogenic, competing microorganis m. Further integration of biologically based methods with conventional management of blossom blight may be achievable by increasing the dive rsity of applied antagonists, by refining predictive models to incorpo rate antagonist use, and by gaining an improved understanding of the i nteractions that occur among indigenous and applied bacterial epiphyte s, antibiotics, and the physical environment.