LABORATORY AND FIELD TRIALS WITH SELECTED MICROORGANISMS AS BIOCONTROL AGENTS FOR FIRE BLIGHT

Epiphytic microorganisms from apple blossoms were assayed for potential as fire blight biocontrol agents using detached crab apple blossoms.
Initial tests were based on the ability of organisms to reduce the population size of Erwinia amylovora on flower stigmas.
To compare strains tested on different dates, the ratio of the population size of E. amylovora on treated flowers to that on control flowers was calculated.
Ratios for strains of Pantoea agglomerans, Pseudomonas spp., and Bacillus spp. were as low as 0.0002, 0.002 and 0.03, respectively.
Some strains were also assayed by subjecting stigma-treated flowers to a 24-hr wetting period and later evaluating flowers for disease severity.
This involved less technical input, but required more flowers to obtain reliable results and more overall time than that of the population-based assay.
The latter method was recently modified by using a bioluminescent strain of E. amylovora and estimating population size with a Luminometer.
This approach was successfully demonstrated and eliminated the need for dilution plating and colony counting.
Field trials were conducted with ‘Jonagold’ apple in 1997 and with ‘Gala’ apple in 1998. Tests were performed using plastic enclosures around single trees to elevate day-time temperatures and prevent bees from transferring biocontrol agents between blossoms.
Also, trees were subjected to artificial wetting.
In these trials, Pantoea agglomerans strain E325 was more effective (P ≤ 0.05) than standard biocontrol agents in reducing disease incidence.

VIII International Workshop on Fire Blight

P.L. Pusey

https://doi.org/10.17660/ActaHortic.1999.489.117