CHALLENGES INVOLVED IN DEPLOYING BACTERIOPHAGES FOR CONTROL OF BACTERIAL PLANT DISEASES. J. B. Jones (1), F. Iriarte (2), B. Balogh (3), A. Obradovic (4), and M. T. Momol (1)
(1) Department of Plant Pathology, University of Florida, Gainesville, FL USA; (2) Department of Plant Pathology, Iowa State University, Ames, IA USA; (3) Department of Plant Pathology & Ecology,The Connecticut Agricultural Experiment Station, New Haven, CT USA; and (4) Plant Pathology Department, Faculty of Agriculture, University of Belgrade, Belgrade-Zemun, Serbia.

Abstract: Biological control using bacteriophages has proven to be an excellent alternative to conventional chemical control strategies for controlling bacterial spot of tomato. In several studies which we conducted, bacteriophages outperformed standard chemical control practices (principally copper-based compounds) and other biological control strategies. One of the major challenges in deploying bacteriophages relates to the ability of phages to persist at levels necessary for being effective in limiting bacterial populations. Persistence of phages in the phyllosphere is influenced by various factors including the presence or absence of the phage host, sunlight irradiation (especially in the UV zone), temperature, desiccation, and copper-based bactericides. These factors were evaluated in two studies (Balogh 2007, Ph.D. dissertation, University of Florida; Iriarte et al., 2007, Appl. & Env. Microbiol. 73:1704-1711) for persistence of non-formulated phage (nothing added to enhance longevity) and formulated phage (phage mixed with skim milk). Field studies were conducted to address the effects of a copper bactericide and sunlight on phage survival. Copper was shown to adversely affect phage if applied the same day as phage applications but not if applied at least 4 days prior to phage application. Sunlight UV was evaluated for detrimental effects on formulated and non-formulated phage survival on tomato foliage in which phage was applied at four time points during the day (early morning, midmorning, early afternoon, and late evening). In that study in which UV (UVA and UVB) irradiation and phage populations were monitored, populations declined most precipitously in the early afternoon when intensity of UV irradiation was highest. Application of phage in the evening resulted in minimal reduction in phage populations on leaf surfaces when assayed the following morning. There was clearly a negative correlation between UV intensity and phage populations with the protective formulation consistently reducing the deleterious effects of UV. In growth room experiments, ambient temperature was shown to have a pronounced effect on non-formulated phage but not on formulated phages. We also 49 determined the effects of desiccation and fluorescent light on phage survival. Desiccation without exposure to light caused a slight decline in phage populations after 60 days, whereas desiccation combined with fluorescent light was much more destructive. The formulation protected phage from adverse effects of both factors. Phage persistence was most dramatically affected by UV, while the other factors had much less pronounced effects. The skim milk formulated phage reduced deleterious effects of the studied environmental factors. Combining the use of formulated phage with evening applications potentially should optimize efficacy. Future research should focus on developing other strategies to optimize stability of phages on the leaf surface.