Bacteriophage-Based Bacterial Wilt Biocontrol for an Environmentally Sustainable Agriculture

Abstract

Bacterial wilt diseases caused by Ralstonia solanacearum, R. pseudosolanacearum, and R. syzygii subsp. indonesiensis (former R. solanacearum species complex) are among the most important plant diseases worldwide, severely affecting a high number of crops and ornamentals. Difficulties of bacterial wilt control by non-biological methods are related to effectiveness, bacterial resistance and environmental impact. Alternatively, a great many biocontrol strategies have been carried out, with the advantage of being environmentally friendly. Advances in bacterial wilt biocontrol include an increasing interest in bacteriophage-based treatments as a promising re-emerging strategy. Bacteriophages against the bacterial wilt pathogens have been described with either lytic or lysogenic effect but, they were proved to be active against strains belonging to R. pseudosolanacearum and/or R. syzygii subsp. indonesiensis, not to the present R. solanacearum species, and only two of them demonstrated successful biocontrol potential in planta. Despite the publication of three patents on the topic, until now no bacteriophage-based product is commercially available. Therefore, there is still much to be done to incorporate valid bacteriophages in an integrated management program to effectively fight bacterial wilt in the field.

Keywords: biological agent; lysogenic phage; lytic phage; management; treatment.

FIGURE 1

Bacterial wilt strains used to test the biocontrol potential of the bacteriophages in planta. Correspondence among the geographical origin of bacterial wilt strains, the species Ralstonia pseudosolanacearum, R. syzygii subsp. indonesiensis, and present R. solanacearum (Safni et al., 2014) (former “R. solanacearum species complex” according to Fegan and Prior, 2005), and previous infraspecific classifications of the species complex in four phylotypes, five races, and five biovars, according to molecular characteristics (Fegan and Prior, 2005), host range (Buddenhagen and Kelman, 1964; Hayward, 1991) and biochemical properties (Hayward, 1964, 1991), respectively. To date, all bacteriophage-based biocontrol assays were performed against Asian bacterial wilt strains, presently not classified as R. solanacearum.