Biological control of the fire blight pathogen Erwinia amylovora using bacteriophages

Abstract

Bacteriophages offer unique benefits for the specific control of Erwinia amylovora, the causative agent of fire blight in pome fruit. Unfortunately, the majority of described phages were tested for efficacy in vitro only. Data from infection assays using pear slices or detached blossoms is rare and field trials are barely reported. It remains to be studied if bacteriophages could control fire blight in the open field. This review summarizes current knowledge of different phages infecting E. amylovora. In addition, the requirements for a phage to optimally function as a biological antimicrobial agent in agriculture are discussed together with the ideal setup of field trials and the formulation of phages for best results.

First European Erwinia amylovora Lytic Bacteriophage Cocktails Effective in the Host: Characterization and Prospects for Fire Blight Biocontrol

“…Despite the high genome homogeneity of the E. amylovora species, bacteriophages active against a set of E. amylovora strains usually lack activity against a more or less considerable percentage of the tested strains [ 24 , 36 , 66 , 67 ].…”

“…It is also worth mentioning that, although some phages or commercial phage products against the fire blight pathogen have demonstrated efficacy against some strains, their efficacy seems to be highly dependent on environmental conditions. Moreover, although E. amylovora is a highly homogeneous species, a great variation in the efficacy of different phages has been described depending on the strain of the pathogen tested [ 24 , 66 , 67 , 84 ]. Therefore, it is important to continue searching for new bacteriophages that can control fire blight outbreaks caused by different E. amylovora strains in a range of environmental settings.…”

“…active against a set of E. amylovora strains usually lack activity against a more or less con-siderable percentage of the tested strains [24,36,66,67].…”

“…However, the use of single bacteriophages can cause the appearance of resistant bacteria, but this can be solved by combining phages with different receptors of the target bacteria in cocktails which allow for reducing the emergence of phage-resistant bacteria as well as expanding the host range [ 23 ]. Using phages under field conditions faces other challenges, mainly the exposure to different types of environmental stresses, such as ultraviolet light, humidity, and temperature changes, as well as the survival of phages in the absence of their host bacteria [ 21 , 24 ]. Despite this, the bacteriophage-based treatment of bacterial plant diseases has received renewed interest in recent years, with several studies reporting promising control activities against important plant pathogenic bacterial species and several commercial phage-based products against some of them, including pathogens of the aerial part of the plant, such as E. amylovora [ 21 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 ].…”

“…A key factor determining bacteriophage treatment efficacy, apart from their lytic nature, is their ability to persist on the phyllosphere. UV light and other environmental factors limit the success of phage application [ 21 , 24 , 40 ]. Some strategies to circumvent these challenges can be planning applications late in the day, working on protective formulations, and using carrier bacteria that minimize the effects of UV irradiation [ 23 , 41 ].…”