According to Jason Gill, a phage researcher at the University of Guelph, Guelph, Ontario, phages have been proposed as plant-pathogen control agents in a process known as phage therapy--the application of phages to ecosystems to reduce the population size of bacteria. "Phage could be explored as a biological control agent--the use of one organism to suppress another," said Gill.
Like other methods of biological control, one advantage of phage therapy is a reduction in the usage of chemical agents against pest species, which, in the case of phage, means a reduction in the usage of chemical antibiotics, said Gill. Another potential benefit of phage therapy is that phages are generally quite specific for their host bacterial species, and so can be targeted towards harmful bacteria while leaving other, potentially beneficial bacteria intact.
Phage therapy has been used successfully against bacterial blotch of mushrooms caused by Pseudomonas tolaasii. In studies notable for the employment of phage host-range mutants, phage therapy has also been employed against bacterial blight of geraniums and bacterial spot of tomatoes, both caused by pathovars of Xanthomonas campestris.
Though seemingly effective in certain situations, it is likely that phage therapy against bacterial plant pathogens will not prove to be a magic bullet in all cases, said Gill. The natural interactions between phages, bacteria, and plants are still not well understood. While phages that attack pathogenic bacteria can help improve plant health, other phages may attack the bacteria that affect the root nodulation of plants such as soybeans, which are necessary for normal plant growth.
The positive and negative effects of using phages to fight plant disease are the subjects of this month's APS feature article that can be found on the APS website at http://www.