ISHS Acta Horticulturae 338: VI International Workshop on Fireblight
POPULATION DYNAMICS OF PSEUDOMONAS FLUORESCENS STRAIN A506 IN PEAR FLOWERS FOLLOWING INOCULATION IN RELATION TO STRATEGIES OF BIOLOGICAL CONTROL OF FIRE BLIGHT AND FROST INJURY. |
| Authors: | S. Lindow, M. Wilson |
| Abstract:
While it is known that single applications of the antagonistic bacterium Pseudomonas fluorescens strain A506 can confer significant fire blight and frost control following a single inoculation onto pear trees at about 20% bloom, it was unknown whether all flowers were colonized following single applications. Optimization of biological control with a minimum number of applications of the antagonist will require knowledge of the extent and rapidity of its movement to flowers which open subsequent to inoculation, particularly to rat-tail flowers which open following the main bloom. Pear trees in commercial orchards (from 16 to 25 trees per replication of each treatment) were sprayed (ca. 4 L/tree) with freeze-dried cells of P. fluorescens strain A506 suspended in water to a final concentration of about 108 cells/ml once at either 5%, 20%, 50%, or 90% bloom, as well as at both 20% and 90% bloom. Bacteria were applied either with commercial air-blast sprayers or a hand-held sprayer. 800 newly-opening flowers were tagged every 3 days to identify flowers that had opened at different times prior to, and after, spray inoculation with strain A506. A subset of the tagged flowers were sampled every 3 days to measure bacterial colonization of the flowers which were open or closed at different times relative to application of the antagonistic bacterium. The population size of bacteria was determined on 20 individual flowers of each age from each treatment at each sampling date. The population size of strain A506 was unambiguously determined on Kings Medium B containing 100μg/ml rifampicin and cycloheximide. Nearly all flowers that opened within 2 weeks of spray inoculation of strain A506 were colonized by this bacterium. The mean population size of strain A506 was about 105 cells/flower in such flowers. Both the incidence of colonization and the average population size of strain A506 decreased in flowers that had opened more than two weeks after spray inoculation. A higher average population size of strain A506 was recovered in flowers sprayed twice with strain A506 than in flowers sprayed only one at any developmental time. The incidence of natural Erwinia amylovora infection was reduced about 75% by strain A506. While a higher reduction of fire blight was observed in trees | |
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