Project Number: 5350-22000-013-00
Project Type: Appropriated

Start Date: Mar 05, 2003
End Date: Mar 11, 2007

Objective:
Advance understanding of nutrient availability and utilization in the ecology of epiphytic microorganisms on the surfaces of pomaceous flowers; determine the role of extracellular metabolites in biological control and in the compatibility of microbial strains considered for use in antagonist mixtures; expand knowledge of the relationship of environmental factors to the blossom blght phase of fire blight and its biological control; and enhance the efficacy of microbial biocontrol and its integration with other management strategies for fire blight.

Approach:
Efforts will be made to identify carbon and nitrogen sources on flower stigmas and hypanthia, and to determine the capacity of strains of the pathogen, Erwinia amylovora, and microbial antagonists to utilize these food sources. Concurrently, the spatial distribution and site preference of different antagonists on flower surfaces will be studied. Antagonists will be selected from among naturally-occurring strains previously evaluated for their use in biocontrol and will represent diverse taxa, including Pantoea agglomerans, Pseudomonas, Bacillus and various yeasts. The role of extracellular metabolites will be studied with defined artificial media consisting of ingredients partly determined by results of previous nutrient studies. Antibiotics or bacteriocins produced by superior antagonist strains will be partially characterized. It is anticipated that strains of P. agglomerans will be of greatest interest, followed by those of Pseudomonas and Bacillus. The relationship of environmental factors to blossom blight will be studied with detached flowers held in controlled environment chambers programmable to simulate typical diurnal fluctuations of temperature and humidity. Variables to be studied in relation to microbial colonization and interaction on flower surfaces include temperature, relative humidity, free moisture, pollination and flower age. Microbial growth resulting from various scenarios of day-to-day changes in temperature will be compared to that predicted according to disease models. Weaknesses in the capacity of microbial antagonists to grow and suppress E. amylovora under these varying conditions will be identified. Knowledge gained from the above investigations will be applied toward improving antagonists or antagonist mixtures. Antagonists will be selected and combined based on individual biocontrol efficacy, capacity to occupy the epiphytic niche of the pathogen, diversity and complementation of mechanisms, and compatibility. Efforts will be made to qualitatively or quantitatively enhance antagonist production of antibiotics and to eliminate incompatibilities between antagonist strains. Studies will also been done to integrate microbial biocontrol agents with other existing or potential management approaches, such as the use of antibiotics and inducers of systemic acquired resistance. Formerly 5350-22000-010-00D (2/03).