Penetration and translocation of Erwinia amylovora-specific bacteriophages in apple - a possibility of enhanced control of fire blight

We have investigated the uptake and delivery of Erwinia amylovora-specific bacteriophages in apple plants. The main aim of this study was to assess the potential of phage application as a means for improving phage persistence and thereby the control of fire blight, the disease caused by E. amylovora. Both phage strains tested (I broken vertical bar Ea104 and H5K) were able to translocate in apple seedlings and were detectable by a modified Adams' drop test and real-time qPCR in plant parts above ground level following their application to the roots. Conversely, phages were detectable in roots after spraying them onto the stem and leaves. A water suspension of phages effectively decreased symptom severity of E. amylovora infection in apple seedlings following treatment of roots or aerial plant parts and application to the cotyledon, as judged by symptom bonitation. A similar effect was achieved by spraying a phage suspension onto flowering firethorn shoots. Interestingly no significant differences in controlling E. amylovora infection were found among the two phage strains tested. It seems that phages specific to E. amylovora can penetrate plants and exhibit a decrease in severity of symptoms caused by the phytopathogen. Demonstrating in planta translocation of E. amylovora-specific bacteriophages and their effect of reducing fire blight symptoms may significantly contribute to a better control of E. amylovora and promote further investigations on penetration and translocation of phages into plants.