Seed coating with phages for sustainable plant biocontrol of plant pathogens and influence of the seed coat mucilage

Pathogens resistant to classical control strategies are on the rise and cause significant damage in crop yield production with seeds as one major transmission route. Bacteriophages are specialized viruses of bacteria and their interaction with seeds holds great potential as targeted and sustainable solution to this problem. In this study, we isolated and characterized two novel phages, Athelas and Alfirin, infecting Pseudomonas syringae and Agrobacterium tumefaciens, respectively, and included the recently published phage Pfeifenkraut infecting Xanthomonas translucens. The three phages were tested for their interaction with the seed coat mucilage. Phage binding on Arabidopsis seeds, which exude the mucilage as a polysaccharide-polymer-matrix, was assessed by comparison to seeds with removed mucilage. Two of the three phages were dependant on mucilage for seed binding, and podophage Athelas showed the highest dependency. Further podoviruses of the Autographiviridae obtained from the systematic E. coli (BASEL) phage collection were tested and showed a similar dependency on the mucilage for seed adhesion. Comparative analysis using a set of Arabidopsis seed coat mutants revealed the diffusible cellulose fraction as important component for phage binding. Long-term activity tests revealed a high stability of phages on seed surfaces and phage coating effectively increased the survival rate of plant seedling in the presence of the pathogen. Utilization of non-virulent host strains was further successfully applied to boost the presence of infectious phage particles on seed surfaces. Altogether, our study highlights the high potential of phage-based applications as sustainable biocontrol strategy on the seed level.