VIEW ARTICLE

Ecology and Epidemiology

Interactions Between the Biological Control Agent Pseudomonas fluorescens A506 and Erwinia amylovora in Pear Blossoms. M. Wilson,Post-doctoral research assistant, Department of Plant Pathology, 147 Hilgard Hall, University of California, Berkeley 94720; S. E. Lindow, professor, Department of Plant Pathology, 147 Hilgard Hall, University of California, Berkeley 94720. Phytopathology 83:117-123. Accepted for publication 19 October 1992. Copyright 1993 The American Phytopathological Society. DOI: 10.1094/Phyto-83-117.

In the greenhouse, Pseudomonas fluorescens strain A506 effectively colonized the pistils of pear blossoms. P. fluorescens A506 significantly reduced colonization of pear pistils by Erwinia amylovora when the biological control agent was inoculated 72 h in advance of the pathogen, but not when it was coinoculated with E. amylovora. P. fluorescens A506 probably excluded E. amylovora by preemptively utilizing a growth-limiting resource required by the pathogen. A506 also colonized the nectaries of pear blossoms, in which it maintained high populations for 60–72 h. A506 significantly reduced colonization of pear nectaries by E. amylovora when it was inoculated 72 h in advance of the pathogen. Although the inhibition of E. amylovora on pear nectaries may involve preemptive utilization of a growth-limiting resource, other factors, such as induced cessation of nectar secretion or accumulation of a host toxin, also may be involved. P. fluorescens A506 probably prevents fire blight infection of pear in the field by preventing epiphytic build-up of pathogen inoculum on pistils and by inhibiting the growth of inoculum deposited on nectaries.